From e4da8cfea56b658d874e603c05f4a57b9a096786 Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Sun, 1 May 2016 18:44:38 -0700
Subject: [PATCH 01/12] Use the standard newline function.

---
 packages/babel-generator/src/generators/expressions.js | 2 +-
 packages/babel-generator/src/generators/statements.js  | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/babel-generator/src/generators/expressions.js b/packages/babel-generator/src/generators/expressions.js
index aaecc7282f..36f0485a91 100644
--- a/packages/babel-generator/src/generators/expressions.js
+++ b/packages/babel-generator/src/generators/expressions.js
@@ -88,7 +88,7 @@ export function Decorator(node: Object) {
 
 function commaSeparatorNewline() {
   this.token(",");
-  this.push("\n");
+  this.newline();
 }
 
 export function CallExpression(node: Object) {
diff --git a/packages/babel-generator/src/generators/statements.js b/packages/babel-generator/src/generators/statements.js
index 9cfeab8d26..38044cacbe 100644
--- a/packages/babel-generator/src/generators/statements.js
+++ b/packages/babel-generator/src/generators/statements.js
@@ -208,14 +208,14 @@ export function DebuggerStatement() {
 function variableDeclarationIdent() {
   // "let " or "var " indentation.
   this.token(",");
-  this.push("\n");
+  this.newline();
   for (let i = 0; i < 4; i++) this.push(" ");
 }
 
 function constDeclarationIdent() {
   // "const " indentation.
   this.token(",");
-  this.push("\n");
+  this.newline();
   for (let i = 0; i < 6; i++) this.push(" ");
 }
 

From 177c092496ab6ff46b5cd3702ad1798a06aa74c1 Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Sat, 2 Jul 2016 12:42:15 -0700
Subject: [PATCH 02/12] Remove sideeffectful position mutation.

---
 packages/babel-generator/src/buffer.js     | 2 +-
 packages/babel-generator/src/index.js      | 2 +-
 packages/babel-generator/src/source-map.js | 7 ++-----
 3 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/packages/babel-generator/src/buffer.js b/packages/babel-generator/src/buffer.js
index 65b35ce16d..750ecac11e 100644
--- a/packages/babel-generator/src/buffer.js
+++ b/packages/babel-generator/src/buffer.js
@@ -333,7 +333,7 @@ export default class Buffer {
     }
 
     // If there the line is ending, adding a new mapping marker is redundant
-    if (this.opts.sourceMaps && str[0] !== "\n") this.map.mark(this._sourcePosition);
+    if (this.opts.sourceMaps && str[0] !== "\n") this.map.mark(this.position, this._sourcePosition);
 
     //
     this.position.push(str);
diff --git a/packages/babel-generator/src/index.js b/packages/babel-generator/src/index.js
index 4254d8bdf9..f13bec1764 100644
--- a/packages/babel-generator/src/index.js
+++ b/packages/babel-generator/src/index.js
@@ -31,7 +31,7 @@ class Generator extends Printer {
     this._inForStatementInitCounter = 0;
 
     this.whitespace = new Whitespace(tokens);
-    this.map        = new SourceMap(position, opts, code);
+    this.map        = new SourceMap(opts, code);
   }
 
   format: {
diff --git a/packages/babel-generator/src/source-map.js b/packages/babel-generator/src/source-map.js
index ca23337e7e..5987e75c44 100644
--- a/packages/babel-generator/src/source-map.js
+++ b/packages/babel-generator/src/source-map.js
@@ -5,8 +5,7 @@ import sourceMap from "source-map";
  */
 
 export default class SourceMap {
-  constructor(position, opts, code) {
-    this.position = position;
+  constructor(opts, code) {
     this.opts     = opts;
     this.last     = {generated: {}, original: {}};
 
@@ -46,12 +45,10 @@ export default class SourceMap {
    * values to insert a mapping to nothing.
    */
 
-  mark(sourcePos: Object) {
+  mark(position, sourcePos: Object) {
     let map = this.map;
     if (!map) return; // no source map
 
-    let position = this.position;
-
     // Adding an empty mapping at the start of a generated line just clutters the map.
     if (this._lastGenLine !== position.line && sourcePos.line === null) return;
 

From 3680d10b6f5dcf28c67fba0e3d7f9fd2689ccc90 Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Sat, 2 Jul 2016 13:22:52 -0700
Subject: [PATCH 03/12] Centralize position tracking into buffer.

---
 packages/babel-generator/src/buffer.js  | 24 +++++++++++++++---------
 packages/babel-generator/src/index.js   |  7 +------
 packages/babel-generator/src/printer.js |  3 +--
 3 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/packages/babel-generator/src/buffer.js b/packages/babel-generator/src/buffer.js
index 750ecac11e..801042dfeb 100644
--- a/packages/babel-generator/src/buffer.js
+++ b/packages/babel-generator/src/buffer.js
@@ -1,4 +1,4 @@
-import type Position from "./position";
+import Position from "./position";
 import repeat from "lodash/repeat";
 import trimEnd from "lodash/trimEnd";
 
@@ -7,10 +7,10 @@ import trimEnd from "lodash/trimEnd";
  */
 
 export default class Buffer {
-  constructor(position: Position, format: Object) {
+  constructor(format: Object) {
     this.printedCommentStarts = {};
     this.parenPushNewlineState = null;
-    this.position = position;
+    this._position = new Position();
     this._indent = format.indent.base;
     this.format = format;
     this.buf = "";
@@ -44,7 +44,7 @@ export default class Buffer {
   catchUp(node: Object) {
     // catch up to this nodes newline if we're behind
     if (node.loc && this.format.retainLines && this.buf) {
-      while (this.position.line < node.loc.start.line) {
+      while (this.getCurrentLine() < node.loc.start.line) {
         this.push("\n");
       }
     }
@@ -164,7 +164,6 @@ export default class Buffer {
     this.push(str);
   }
 
-
   /**
    * Remove the last character.
    */
@@ -178,7 +177,7 @@ export default class Buffer {
     if (!this.endsWith(cha)) return;
     this.buf = this.buf.slice(0, -1);
     this.last = this.buf[this.buf.length - 1];
-    this.position.unshift(cha);
+    this._position.unshift(cha);
   }
 
   /**
@@ -260,7 +259,7 @@ export default class Buffer {
       let toRemove = this.buf.slice(lastNewlineIndex + 1);
       this.buf = this.buf.substring(0, lastNewlineIndex + 1);
       this.last = "\n";
-      this.position.unshift(toRemove);
+      this._position.unshift(toRemove);
     }
   }
 
@@ -333,10 +332,10 @@ export default class Buffer {
     }
 
     // If there the line is ending, adding a new mapping marker is redundant
-    if (this.opts.sourceMaps && str[0] !== "\n") this.map.mark(this.position, this._sourcePosition);
+    if (this.opts.sourceMaps && str[0] !== "\n") this.map.mark(this._position, this._sourcePosition);
 
     //
-    this.position.push(str);
+    this._position.push(str);
     this.buf += str;
     this.last = str[str.length - 1];
 
@@ -358,4 +357,11 @@ export default class Buffer {
     }
   }
 
+  getCurrentColumn() {
+    return this._position.column;
+  }
+
+  getCurrentLine() {
+    return this._position.line;
+  }
 }
diff --git a/packages/babel-generator/src/index.js b/packages/babel-generator/src/index.js
index f13bec1764..ffc9faca04 100644
--- a/packages/babel-generator/src/index.js
+++ b/packages/babel-generator/src/index.js
@@ -1,7 +1,6 @@
 import detectIndent from "detect-indent";
 import Whitespace from "./whitespace";
 import SourceMap from "./source-map";
-import Position from "./position";
 import * as messages from "babel-messages";
 import Printer from "./printer";
 
@@ -18,12 +17,9 @@ class Generator extends Printer {
     let tokens   = ast.tokens || [];
     let format   = Generator.normalizeOptions(code, opts, tokens);
 
-    let position = new Position;
-
-    super(position, format);
+    super(format);
 
     this.comments = comments;
-    this.position = position;
     this.tokens   = tokens;
     this.format   = format;
     this.opts     = opts;
@@ -54,7 +50,6 @@ class Generator extends Printer {
   auxiliaryCommentBefore: string;
   auxiliaryCommentAfter: string;
   whitespace: Whitespace;
-  position: Position;
   map: SourceMap;
   comments: Array<Object>;
   tokens: Array<Object>;
diff --git a/packages/babel-generator/src/printer.js b/packages/babel-generator/src/printer.js
index 98690a3468..79fcb230fa 100644
--- a/packages/babel-generator/src/printer.js
+++ b/packages/babel-generator/src/printer.js
@@ -272,7 +272,6 @@ export default class Printer extends Buffer {
 
       if (!this.endsWith(["[", "{"])) this.space();
 
-      let column = this.position.column;
       let val    = this.generateComment(comment);
 
       //
@@ -283,7 +282,7 @@ export default class Printer extends Buffer {
           val = val.replace(newlineRegex, "\n");
         }
 
-        let indent = Math.max(this.indentSize(), column);
+        let indent = Math.max(this.indentSize(), this.getCurrentColumn());
         val = val.replace(/\n/g, `\n${repeat(" ", indent)}`);
       }
 

From d6b1e36d4908ca30f9f5d3a527c9c5741aefd424 Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Sat, 2 Jul 2016 15:31:30 -0700
Subject: [PATCH 04/12] Make the 'catchUp' call implicit to source location
 updates.

---
 packages/babel-generator/src/buffer.js             | 14 ++++++--------
 packages/babel-generator/src/printer.js            |  6 +-----
 .../expected.js                                    |  4 +++-
 .../return-with-retainlines-option/expected.js     |  7 ++++---
 4 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/packages/babel-generator/src/buffer.js b/packages/babel-generator/src/buffer.js
index 801042dfeb..a5fc0e432c 100644
--- a/packages/babel-generator/src/buffer.js
+++ b/packages/babel-generator/src/buffer.js
@@ -37,14 +37,10 @@ export default class Buffer {
   buf: string;
   last: string;
 
-  /**
-   * Description
-   */
-
-  catchUp(node: Object) {
+  _catchUp(){
     // catch up to this nodes newline if we're behind
-    if (node.loc && this.format.retainLines && this.buf) {
-      while (this.getCurrentLine() < node.loc.start.line) {
+    if (this.format.retainLines && this._sourcePosition.line !== null) {
+      while (this.getCurrentLine() < this._sourcePosition.line) {
         this.push("\n");
       }
     }
@@ -276,6 +272,8 @@ export default class Buffer {
     this._sourcePosition.line = pos ? pos.line : null;
     this._sourcePosition.column = pos ? pos.column : null;
     this._sourcePosition.filename = loc && loc.filename || null;
+
+    this._catchUp();
   }
 
   /**
@@ -283,7 +281,7 @@ export default class Buffer {
    */
 
   withSource(prop: string, loc: Location, cb: () => void) {
-    if (!this.opts.sourceMaps) return cb();
+    if (!this.opts.sourceMaps && !this.format.retainLines) return cb();
 
     // Use the call stack to manage a stack of "source location" data.
     let originalLine = this._sourcePosition.line;
diff --git a/packages/babel-generator/src/printer.js b/packages/babel-generator/src/printer.js
index 79fcb230fa..f14ca8f99e 100644
--- a/packages/babel-generator/src/printer.js
+++ b/packages/babel-generator/src/printer.js
@@ -45,8 +45,6 @@ export default class Printer extends Buffer {
 
     this.printLeadingComments(node, parent);
 
-    this.catchUp(node);
-
     this._printNewline(true, node, parent, opts);
 
     if (opts.before) opts.before();
@@ -264,9 +262,7 @@ export default class Printer extends Buffer {
     }
 
     // Exclude comments from source mappings since they will only clutter things.
-    this.withSource(null, null, () => {
-      this.catchUp(comment);
-
+    this.withSource("start", comment.loc, () => {
       // whitespace before
       this.newline(this.whitespace.getNewlinesBefore(comment));
 
diff --git a/packages/babel-generator/test/fixtures/edgecase/return-with-retainlines-and-compact-option/expected.js b/packages/babel-generator/test/fixtures/edgecase/return-with-retainlines-and-compact-option/expected.js
index 7441245e8e..d13817e5aa 100644
--- a/packages/babel-generator/test/fixtures/edgecase/return-with-retainlines-and-compact-option/expected.js
+++ b/packages/babel-generator/test/fixtures/edgecase/return-with-retainlines-and-compact-option/expected.js
@@ -1,4 +1,6 @@
 function foo(l){
 return(
 
-l);}
+l);
+
+}
diff --git a/packages/babel-generator/test/fixtures/edgecase/return-with-retainlines-option/expected.js b/packages/babel-generator/test/fixtures/edgecase/return-with-retainlines-option/expected.js
index cc911760dc..fd1cba7b14 100644
--- a/packages/babel-generator/test/fixtures/edgecase/return-with-retainlines-option/expected.js
+++ b/packages/babel-generator/test/fixtures/edgecase/return-with-retainlines-option/expected.js
@@ -1,10 +1,11 @@
 function foo(l) {
   return (
-    l);}
-
+    l);
 
+}
 
 function foo() {
   return (
     1 && 2 || 
-    3);}
+    3);
+}

From 80cd3ca331a796b2f560ec703ac3aa1ffc4ed25a Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Sat, 2 Jul 2016 15:36:12 -0700
Subject: [PATCH 05/12] Drop one usage of removeLast.

---
 packages/babel-generator/src/buffer.js | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/packages/babel-generator/src/buffer.js b/packages/babel-generator/src/buffer.js
index a5fc0e432c..bd7ab81b0f 100644
--- a/packages/babel-generator/src/buffer.js
+++ b/packages/babel-generator/src/buffer.js
@@ -238,7 +238,6 @@ export default class Buffer {
       this.removeLast("\n");
     }
 
-    this.removeLast(" ");
     this._removeSpacesAfterLastNewline();
     for (let j = 0; j < i; j++) {
       this.push("\n");
@@ -250,12 +249,13 @@ export default class Buffer {
    */
 
   _removeSpacesAfterLastNewline() {
-    let lastNewlineIndex = this.buf.lastIndexOf("\n");
-    if (lastNewlineIndex >= 0 && this.get().length <= lastNewlineIndex) {
-      let toRemove = this.buf.slice(lastNewlineIndex + 1);
-      this.buf = this.buf.substring(0, lastNewlineIndex + 1);
-      this.last = "\n";
-      this._position.unshift(toRemove);
+    const originalBuf = this.buf;
+    this.buf = this.buf.replace(/[ \t]+$/, "");
+
+    if (originalBuf.length !== this.buf.length){
+      const removed = originalBuf.slice(this.buf.length);
+      this._position.unshift(removed);
+      this.last = this.buf[this.buf.length - 1];
     }
   }
 

From 578f48134b4113fef6040ec779efd6548b1482ef Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Tue, 26 Apr 2016 09:22:27 -0700
Subject: [PATCH 06/12] Remove removeLast usage.

---
 packages/babel-generator/src/buffer.js | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/packages/babel-generator/src/buffer.js b/packages/babel-generator/src/buffer.js
index bd7ab81b0f..3edee6eeec 100644
--- a/packages/babel-generator/src/buffer.js
+++ b/packages/babel-generator/src/buffer.js
@@ -103,7 +103,8 @@ export default class Buffer {
    */
 
   rightBrace() {
-    this.newline(true);
+    if (!this.endsWith("\n")) this.newline();
+
     if (this.format.minified && !this._lastPrintedIsEmptyStatement) {
       this._removeLast(";");
     }
@@ -212,10 +213,9 @@ export default class Buffer {
 
   /**
    * Add a newline (or many newlines), maintaining formatting.
-   * Strips multiple newlines if removeLast is true.
    */
 
-  newline(i?: boolean | number, removeLast?: boolean) {
+  newline(i?: number) {
     if (this.format.retainLines || this.format.compact) return;
 
     if (this.format.concise) {
@@ -226,18 +226,12 @@ export default class Buffer {
     // never allow more than two lines
     if (this.endsWith("\n\n")) return;
 
-    if (typeof i === "boolean") removeLast = i;
     if (typeof i !== "number") i = 1;
 
     i = Math.min(2, i);
     if (this.endsWith("{\n") || this.endsWith(":\n")) i--;
     if (i <= 0) return;
 
-    // remove the last newline
-    if (removeLast) {
-      this.removeLast("\n");
-    }
-
     this._removeSpacesAfterLastNewline();
     for (let j = 0; j < i; j++) {
       this.push("\n");

From caef91672d0e8c4f154a1cb108b505e9954c627f Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Sun, 1 May 2016 18:42:33 -0700
Subject: [PATCH 07/12] Remove unnecessary passthrough function.

---
 packages/babel-generator/src/buffer.js | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/packages/babel-generator/src/buffer.js b/packages/babel-generator/src/buffer.js
index 3edee6eeec..2f778535d8 100644
--- a/packages/babel-generator/src/buffer.js
+++ b/packages/babel-generator/src/buffer.js
@@ -106,7 +106,7 @@ export default class Buffer {
     if (!this.endsWith("\n")) this.newline();
 
     if (this.format.minified && !this._lastPrintedIsEmptyStatement) {
-      this._removeLast(";");
+      this.removeLast(";");
     }
     this.token("}");
   }
@@ -166,11 +166,6 @@ export default class Buffer {
    */
 
   removeLast(cha: string) {
-    if (this.format.compact) return;
-    return this._removeLast(cha);
-  }
-
-  _removeLast(cha: string) {
     if (!this.endsWith(cha)) return;
     this.buf = this.buf.slice(0, -1);
     this.last = this.buf[this.buf.length - 1];

From f908f3fc88dd56910b5f42f201ca61145f1f69a5 Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Sun, 3 Jul 2016 20:35:57 -0700
Subject: [PATCH 08/12] Use 'push' for all cases.

---
 packages/babel-generator/src/buffer.js                | 4 ++--
 packages/babel-generator/src/generators/statements.js | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/packages/babel-generator/src/buffer.js b/packages/babel-generator/src/buffer.js
index 2f778535d8..204641d60d 100644
--- a/packages/babel-generator/src/buffer.js
+++ b/packages/babel-generator/src/buffer.js
@@ -124,10 +124,10 @@ export default class Buffer {
    * Add a space to the buffer unless it is compact.
    */
 
-  space() {
+  space(force: boolean = false) {
     if (this.format.compact) return;
 
-    if (this.buf && !this.endsWith(" ") && !this.endsWith("\n")) {
+    if ((this.buf && !this.endsWith(" ") && !this.endsWith("\n")) || force) {
       this.push(" ");
     }
   }
diff --git a/packages/babel-generator/src/generators/statements.js b/packages/babel-generator/src/generators/statements.js
index 38044cacbe..e4aa15fd50 100644
--- a/packages/babel-generator/src/generators/statements.js
+++ b/packages/babel-generator/src/generators/statements.js
@@ -209,14 +209,14 @@ function variableDeclarationIdent() {
   // "let " or "var " indentation.
   this.token(",");
   this.newline();
-  for (let i = 0; i < 4; i++) this.push(" ");
+  for (let i = 0; i < 4; i++) this.space(true);
 }
 
 function constDeclarationIdent() {
   // "const " indentation.
   this.token(",");
   this.newline();
-  for (let i = 0; i < 6; i++) this.push(" ");
+  for (let i = 0; i < 6; i++) this.space(true);
 }
 
 export function VariableDeclaration(node: Object, parent: Object) {

From abb9618e8c43fc7baebefd4d635014c4e5427305 Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Tue, 5 Jul 2016 18:09:54 -0700
Subject: [PATCH 09/12] Drop array support from endsWith.

---
 packages/babel-generator/src/buffer.js  | 2 --
 packages/babel-generator/src/printer.js | 2 +-
 2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/packages/babel-generator/src/buffer.js b/packages/babel-generator/src/buffer.js
index 204641d60d..0b691e4be0 100644
--- a/packages/babel-generator/src/buffer.js
+++ b/packages/babel-generator/src/buffer.js
@@ -335,8 +335,6 @@ export default class Buffer {
    */
 
   endsWith(str: string): boolean {
-    if (Array.isArray(str)) return str.some((s) => this.endsWith(s));
-
     if (str.length === 1) {
       return this.last === str;
     } else {
diff --git a/packages/babel-generator/src/printer.js b/packages/babel-generator/src/printer.js
index f14ca8f99e..3efe5437c2 100644
--- a/packages/babel-generator/src/printer.js
+++ b/packages/babel-generator/src/printer.js
@@ -266,7 +266,7 @@ export default class Printer extends Buffer {
       // whitespace before
       this.newline(this.whitespace.getNewlinesBefore(comment));
 
-      if (!this.endsWith(["[", "{"])) this.space();
+      if (!this.endsWith("[") && !this.endsWith("{")) this.space();
 
       let val    = this.generateComment(comment);
 

From c5a6c5c291b0295973289c2e4a1da9ff0f389e3b Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Tue, 5 Jul 2016 20:16:12 -0700
Subject: [PATCH 10/12] Pass values directly to avoid object usage.

---
 packages/babel-generator/src/buffer.js     |  3 ++-
 packages/babel-generator/src/source-map.js | 21 +++++++++++----------
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/packages/babel-generator/src/buffer.js b/packages/babel-generator/src/buffer.js
index 0b691e4be0..d7b24a2b65 100644
--- a/packages/babel-generator/src/buffer.js
+++ b/packages/babel-generator/src/buffer.js
@@ -319,7 +319,8 @@ export default class Buffer {
     }
 
     // If there the line is ending, adding a new mapping marker is redundant
-    if (this.opts.sourceMaps && str[0] !== "\n") this.map.mark(this._position, this._sourcePosition);
+    if (this.opts.sourceMaps && str[0] !== "\n") this.map.mark(this._position, this._sourcePosition.line,
+      this._sourcePosition.column, this._sourcePosition.filename);
 
     //
     this._position.push(str);
diff --git a/packages/babel-generator/src/source-map.js b/packages/babel-generator/src/source-map.js
index 5987e75c44..36bfe89097 100644
--- a/packages/babel-generator/src/source-map.js
+++ b/packages/babel-generator/src/source-map.js
@@ -1,4 +1,5 @@
 import sourceMap from "source-map";
+import type Position from "./position";
 
 /**
  * Build a sourcemap.
@@ -45,33 +46,33 @@ export default class SourceMap {
    * values to insert a mapping to nothing.
    */
 
-  mark(position, sourcePos: Object) {
+  mark(position: Position, line: number, column: number, filename: ?string) {
     let map = this.map;
     if (!map) return; // no source map
 
     // Adding an empty mapping at the start of a generated line just clutters the map.
-    if (this._lastGenLine !== position.line && sourcePos.line === null) return;
+    if (this._lastGenLine !== position.line && line === null) return;
 
     // If this mapping points to the same source location as the last one, we can ignore it since
     // the previous one covers it.
-    if (this._lastGenLine === position.line && this._lastSourceLine === sourcePos.line &&
-      this._lastSourceColumn === sourcePos.column) {
+    if (this._lastGenLine === position.line && this._lastSourceLine === line &&
+      this._lastSourceColumn === column) {
       return;
     }
 
     this._lastGenLine = position.line;
-    this._lastSourceLine = sourcePos.line;
-    this._lastSourceColumn = sourcePos.column;
+    this._lastSourceLine = line;
+    this._lastSourceColumn = column;
 
     map.addMapping({
       generated: {
         line: position.line,
         column: position.column
       },
-      source: sourcePos.line == null ? null : sourcePos.filename || this.opts.sourceFileName,
-      original: sourcePos.line == null ? null : {
-        line: sourcePos.line,
-        column: sourcePos.column,
+      source: line == null ? null : filename || this.opts.sourceFileName,
+      original: line == null ? null : {
+        line: line,
+        column: column,
       },
     });
   }

From cb60808500100d391326cb8d82ae9ba34a21f1bc Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Mon, 4 Jul 2016 16:21:32 -0700
Subject: [PATCH 11/12] Make buffer a property for managing the token queue.

---
 packages/babel-generator/src/buffer.js        | 355 ++++--------------
 .../babel-generator/src/generators/base.js    |   2 +-
 packages/babel-generator/src/index.js         |  11 +-
 packages/babel-generator/src/printer.js       | 287 ++++++++++++--
 4 files changed, 343 insertions(+), 312 deletions(-)

diff --git a/packages/babel-generator/src/buffer.js b/packages/babel-generator/src/buffer.js
index d7b24a2b65..5bb911bbfc 100644
--- a/packages/babel-generator/src/buffer.js
+++ b/packages/babel-generator/src/buffer.js
@@ -1,251 +1,99 @@
 import Position from "./position";
-import repeat from "lodash/repeat";
+import type SourceMap from "./source-map";
 import trimEnd from "lodash/trimEnd";
 
 /**
- * Buffer for collecting generated output.
+ * The Buffer class exists to manage the queue of tokens being pushed onto the output string
+ * in such a way that the final string buffer is treated as write-only until the final .get()
+ * call. This allows V8 to optimize the output efficiently by not requiring it to store the
+ * string in contiguous memory.
  */
 
 export default class Buffer {
-  constructor(format: Object) {
-    this.printedCommentStarts = {};
-    this.parenPushNewlineState = null;
-    this._position = new Position();
-    this._indent = format.indent.base;
-    this.format = format;
-    this.buf = "";
-
-    // Maintaining a reference to the last char in the buffer is an optimization
-    // to make sure that v8 doesn't "flatten" the string more often than needed
-    // see https://github.com/babel/babel/pull/3283 for details.
-    this.last = "";
-
-    this.map = null;
-    this._sourcePosition = {
-      line: null,
-      column: null,
-      filename: null,
-    };
-    this._endsWithWord = false;
+  constructor(map: ?SourceMap) {
+    this._map = map;
   }
 
-  printedCommentStarts: Object;
-  parenPushNewlineState: ?Object;
-  position: Position;
-  _indent: number;
-  format: Object;
-  buf: string;
-  last: string;
+  _map: SourceMap = null;
+  _buf: string = "";
+  _last: string = "";
+  _queue: Array = [];
 
-  _catchUp(){
-    // catch up to this nodes newline if we're behind
-    if (this.format.retainLines && this._sourcePosition.line !== null) {
-      while (this.getCurrentLine() < this._sourcePosition.line) {
-        this.push("\n");
-      }
-    }
-  }
+  _position: Position = new Position;
+  _sourcePosition: Object = {
+    line: null,
+    column: null,
+    filename: null,
+  };
 
   /**
-   * Get the current trimmed buffer.
+   * Get the final string output from the buffer, along with the sourcemap if one exists.
    */
 
-  get(): string {
-    return trimEnd(this.buf);
-  }
-
-  /**
-   * Get the current indent.
-   */
-
-  getIndent(): string {
-    if (this.format.compact || this.format.concise) {
-      return "";
-    } else {
-      return repeat(this.format.indent.style, this._indent);
-    }
-  }
-
-  /**
-   * Get the current indent size.
-   */
-
-  indentSize(): number {
-    return this.getIndent().length;
-  }
-
-  /**
-   * Increment indent size.
-   */
-
-  indent() {
-    this._indent++;
-  }
-
-  /**
-   * Decrement indent size.
-   */
-
-  dedent() {
-    this._indent--;
-  }
-
-  /**
-   * Add a semicolon to the buffer.
-   */
-
-  semicolon() {
-    this.token(";");
-  }
-
-  /**
-   * Add a right brace to the buffer.
-   */
-
-  rightBrace() {
-    if (!this.endsWith("\n")) this.newline();
-
-    if (this.format.minified && !this._lastPrintedIsEmptyStatement) {
-      this.removeLast(";");
-    }
-    this.token("}");
-  }
-
-  /**
-   * Add a keyword to the buffer.
-   */
-
-  keyword(name: string) {
-    this.word(name);
-    this.space();
-  }
-
-  /**
-   * Add a space to the buffer unless it is compact.
-   */
-
-  space(force: boolean = false) {
-    if (this.format.compact) return;
-
-    if ((this.buf && !this.endsWith(" ") && !this.endsWith("\n")) || force) {
-      this.push(" ");
-    }
-  }
-
-  /**
-   * Writes a token that can't be safely parsed without taking whitespace into account.
-   */
-
-  word(str: string) {
-    if (this._endsWithWord) this.push(" ");
-
-    this.push(str);
-    this._endsWithWord = true;
-  }
-
-  /**
-   * Writes a simple token.
-   */
-
-  token(str: string) {
-    // space is mandatory to avoid outputting <!--
-    // http://javascript.spec.whatwg.org/#comment-syntax
-    if ((str === "--" && this.last === "!") ||
-
-      // Need spaces for operators of the same kind to avoid: `a+++b`
-      (str[0] === "+" && this.last === "+") ||
-      (str[0] === "-" && this.last === "-")) {
-      this.push(" ");
-    }
-
-    this.push(str);
-  }
-
-  /**
-   * Remove the last character.
-   */
-
-  removeLast(cha: string) {
-    if (!this.endsWith(cha)) return;
-    this.buf = this.buf.slice(0, -1);
-    this.last = this.buf[this.buf.length - 1];
-    this._position.unshift(cha);
-  }
-
-  /**
-   * Set some state that will be modified if a newline has been inserted before any
-   * non-space characters.
-   *
-   * This is to prevent breaking semantics for terminatorless separator nodes. eg:
-   *
-   *    return foo;
-   *
-   * returns `foo`. But if we do:
-   *
-   *   return
-   *   foo;
-   *
-   *  `undefined` will be returned and not `foo` due to the terminator.
-   */
-
-  startTerminatorless(): Object {
-    return this.parenPushNewlineState = {
-      printed: false
+  get(): Object {
+    return {
+      code: trimEnd(this._buf),
+      map: this._map ? this._map.get() : null,
     };
   }
 
   /**
-   * Print an ending parentheses if a starting one has been printed.
+   * Add a string to the buffer that cannot be reverted.
    */
 
-  endTerminatorless(state: Object) {
-    if (state.printed) {
-      this.dedent();
-      this.newline();
-      this.token(")");
-    }
+  append(str: string): void {
+    // If there the line is ending, adding a new mapping marker is redundant
+    if (this._map && str[0] !== "\n") this._map.mark(this._position, this._sourcePosition.line,
+      this._sourcePosition.column, this._sourcePosition.filename);
+
+    this._buf += str;
+    this._last = str[str.length - 1];
+    this._position.push(str);
   }
 
   /**
-   * Add a newline (or many newlines), maintaining formatting.
+   * Add a string to the buffer than can be reverted.
    */
 
-  newline(i?: number) {
-    if (this.format.retainLines || this.format.compact) return;
-
-    if (this.format.concise) {
-      this.space();
-      return;
-    }
-
-    // never allow more than two lines
-    if (this.endsWith("\n\n")) return;
-
-    if (typeof i !== "number") i = 1;
-
-    i = Math.min(2, i);
-    if (this.endsWith("{\n") || this.endsWith(":\n")) i--;
-    if (i <= 0) return;
-
-    this._removeSpacesAfterLastNewline();
-    for (let j = 0; j < i; j++) {
-      this.push("\n");
-    }
+  queue(str: string): void {
+    this.append(str);
   }
 
-  /**
-   * If buffer ends with a newline and some spaces after it, trim those spaces.
-   */
+  removeTrailingSpaces(): void {
+    const oldBuf = this._buf;
+    this._buf = this._buf.replace(/[ \t]+$/, "");
+    this._last = this._buf[this._buf.length - 1];
+    this._position.unshift(oldBuf.slice(this._buf.length));
+  }
 
-  _removeSpacesAfterLastNewline() {
-    const originalBuf = this.buf;
-    this.buf = this.buf.replace(/[ \t]+$/, "");
+  removeTrailingNewline(): void {
+    if (this._last !== "\n") return;
 
-    if (originalBuf.length !== this.buf.length){
-      const removed = originalBuf.slice(this.buf.length);
-      this._position.unshift(removed);
-      this.last = this.buf[this.buf.length - 1];
-    }
+    this._buf = this._buf.slice(0, -1);
+    this._last = this._buf[this._buf.length - 1];
+    this._position.unshift("\n");
+  }
+
+  removeLastSemicolon(): void {
+    if (this._last !== ";") return;
+
+    this._buf = this._buf.slice(0, -1);
+    this._last = this._buf[this._buf.length - 1];
+    this._position.unshift(";");
+  }
+
+  endsWith(str: string): boolean {
+    if (str.length === 1) return str === this._last;
+
+    return this._buf.slice(-str.length) === str;
+  }
+
+  getLast(): string {
+    return this._last;
+  }
+
+  hasContent(): boolean {
+    return !!this._last;
   }
 
   /**
@@ -253,7 +101,7 @@ export default class Buffer {
    * will be given this position in the sourcemap.
    */
 
-  source(prop: string, loc: Location) {
+  source(prop: string, loc: Location): void {
     if (prop && !loc) return;
 
     let pos = loc ? loc[prop] : null;
@@ -261,16 +109,14 @@ export default class Buffer {
     this._sourcePosition.line = pos ? pos.line : null;
     this._sourcePosition.column = pos ? pos.column : null;
     this._sourcePosition.filename = loc && loc.filename || null;
-
-    this._catchUp();
   }
 
   /**
    * Call a callback with a specific source location and restore on completion.
    */
 
-  withSource(prop: string, loc: Location, cb: () => void) {
-    if (!this.opts.sourceMaps && !this.format.retainLines) return cb();
+  withSource(prop: string, loc: Location, cb: () => void): void {
+    if (!this._map) return cb();
 
     // Use the call stack to manage a stack of "source location" data.
     let originalLine = this._sourcePosition.line;
@@ -286,68 +132,11 @@ export default class Buffer {
     this._sourcePosition.filename = originalFilename;
   }
 
-  /**
-   * Push a string to the buffer, maintaining indentation and newlines.
-   */
-
-  push(str: string) {
-    if (!this.format.compact && this._indent && str[0] !== "\n") {
-      // we've got a newline before us so prepend on the indentation
-      if (this.endsWith("\n")) str = this.getIndent() + str;
-    }
-
-    // see startTerminatorless() instance method
-    let parenPushNewlineState = this.parenPushNewlineState;
-    if (parenPushNewlineState) {
-      for (let i = 0; i < str.length; i++) {
-        let cha = str[i];
-
-        // we can ignore spaces since they wont interupt a terminatorless separator
-        if (cha === " ") continue;
-
-        this.parenPushNewlineState = null;
-
-        if (cha === "\n" || cha === "/") {
-          // we're going to break this terminator expression so we need to add a parentheses
-          str = "(" + str;
-          this.indent();
-          parenPushNewlineState.printed = true;
-        }
-
-        break;
-      }
-    }
-
-    // If there the line is ending, adding a new mapping marker is redundant
-    if (this.opts.sourceMaps && str[0] !== "\n") this.map.mark(this._position, this._sourcePosition.line,
-      this._sourcePosition.column, this._sourcePosition.filename);
-
-    //
-    this._position.push(str);
-    this.buf += str;
-    this.last = str[str.length - 1];
-
-    // Clear any state-tracking flags that may have been set.
-    this._endsWithWord = false;
-  }
-
-  /**
-   * Test if the buffer ends with a string.
-   */
-
-  endsWith(str: string): boolean {
-    if (str.length === 1) {
-      return this.last === str;
-    } else {
-      return this.buf.slice(-str.length) === str;
-    }
-  }
-
-  getCurrentColumn() {
+  getCurrentColumn(): number {
     return this._position.column;
   }
 
-  getCurrentLine() {
+  getCurrentLine(): number {
     return this._position.line;
   }
 }
diff --git a/packages/babel-generator/src/generators/base.js b/packages/babel-generator/src/generators/base.js
index 6765bc762e..bceaf00521 100644
--- a/packages/babel-generator/src/generators/base.js
+++ b/packages/babel-generator/src/generators/base.js
@@ -21,7 +21,7 @@ export function BlockStatement(node: Object) {
     if (node.directives && node.directives.length) this.newline();
 
     this.printSequence(node.body, node, { indent: true });
-    if (!this.format.retainLines && !this.format.concise) this.removeLast("\n");
+    if (!this.format.retainLines && !this.format.concise) this.removeTrailingNewline();
 
     this.source("end", node.loc);
     this.rightBrace();
diff --git a/packages/babel-generator/src/index.js b/packages/babel-generator/src/index.js
index ffc9faca04..aa3a6150cb 100644
--- a/packages/babel-generator/src/index.js
+++ b/packages/babel-generator/src/index.js
@@ -17,7 +17,9 @@ class Generator extends Printer {
     let tokens   = ast.tokens || [];
     let format   = Generator.normalizeOptions(code, opts, tokens);
 
-    super(format);
+    let map        = opts.sourceMaps ? new SourceMap(opts, code) : null;
+
+    super(format, map);
 
     this.comments = comments;
     this.tokens   = tokens;
@@ -27,7 +29,6 @@ class Generator extends Printer {
     this._inForStatementInitCounter = 0;
 
     this.whitespace = new Whitespace(tokens);
-    this.map        = new SourceMap(opts, code);
   }
 
   format: {
@@ -50,7 +51,6 @@ class Generator extends Printer {
   auxiliaryCommentBefore: string;
   auxiliaryCommentAfter: string;
   whitespace: Whitespace;
-  map: SourceMap;
   comments: Array<Object>;
   tokens: Array<Object>;
   opts: Object;
@@ -148,10 +148,7 @@ class Generator extends Printer {
     this.print(this.ast);
     this.printAuxAfterComment();
 
-    return {
-      map:  this.map.get(),
-      code: this.get()
-    };
+    return this._buf.get();
   }
 }
 
diff --git a/packages/babel-generator/src/printer.js b/packages/babel-generator/src/printer.js
index 3efe5437c2..f8ec23ebe7 100644
--- a/packages/babel-generator/src/printer.js
+++ b/packages/babel-generator/src/printer.js
@@ -5,12 +5,257 @@ import Buffer from "./buffer";
 import * as n from "./node";
 import * as t from "babel-types";
 
-export default class Printer extends Buffer {
-  constructor(...args) {
-    super(...args);
+export default class Printer {
+  constructor(format, map) {
+    this._format = format || {};
+    this._buf = new Buffer(map);
     this.insideAux = false;
     this.printAuxAfterOnNextUserNode = false;
     this._printStack = [];
+    this.printedCommentStarts = {};
+    this.parenPushNewlineState = null;
+    this._indent = 0;
+  }
+
+  printedCommentStarts: Object;
+  parenPushNewlineState: ?Object;
+
+  /**
+   * Get the current indent.
+   */
+
+  _getIndent(): string {
+    if (this._format.compact || this._format.concise) {
+      return "";
+    } else {
+      return repeat(this._format.indent.style, this._indent);
+    }
+  }
+
+  /**
+   * Increment indent size.
+   */
+
+  indent(): void {
+    this._indent++;
+  }
+
+  /**
+   * Decrement indent size.
+   */
+
+  dedent(): void {
+    this._indent--;
+  }
+
+  /**
+   * Add a semicolon to the buffer.
+   */
+
+  semicolon(): void {
+    this._append(";", true /* queue */);
+  }
+
+  /**
+   * Add a right brace to the buffer.
+   */
+
+  rightBrace(): void {
+    if (!this.endsWith("\n")) this.newline();
+
+    if (this._format.minified && !this._lastPrintedIsEmptyStatement) {
+      this._buf.removeLastSemicolon();
+    }
+    this.token("}");
+  }
+
+  /**
+   * Add a keyword to the buffer.
+   */
+
+  keyword(name: string): void {
+    this.word(name);
+    this.space();
+  }
+
+  /**
+   * Add a space to the buffer unless it is compact.
+   */
+
+  space(force: boolean = false): void {
+    if (this._format.compact) return;
+
+    if ((this._buf.hasContent() && !this.endsWith(" ") && !this.endsWith("\n")) || force) {
+      this._space();
+    }
+  }
+
+  /**
+   * Writes a token that can't be safely parsed without taking whitespace into account.
+   */
+
+  word(str: string): void {
+    if (this._endsWithWord) this._space();
+
+    this._append(str);
+
+    this._endsWithWord = true;
+  }
+
+  /**
+   * Writes a simple token.
+   */
+
+  token(str: string): void {
+    const last = this._buf.getLast();
+    // space is mandatory to avoid outputting <!--
+    // http://javascript.spec.whatwg.org/#comment-syntax
+    if ((str === "--" && last === "!") ||
+
+      // Need spaces for operators of the same kind to avoid: `a+++b`
+      (str[0] === "+" && last === "+") ||
+      (str[0] === "-" && last === "-")) {
+      this._space();
+    }
+
+    this._append(str);
+  }
+
+  /**
+   * Add a newline (or many newlines), maintaining formatting.
+   */
+
+  newline(i?: number): void {
+    if (this._format.retainLines || this._format.compact) return;
+
+    if (this._format.concise) {
+      this.space();
+      return;
+    }
+
+    // never allow more than two lines
+    if (this.endsWith("\n\n")) return;
+
+    if (typeof i !== "number") i = 1;
+
+    i = Math.min(2, i);
+    if (this.endsWith("{\n") || this.endsWith(":\n")) i--;
+    if (i <= 0) return;
+
+    this._buf.removeTrailingSpaces();
+    for (let j = 0; j < i; j++) {
+      this._newline();
+    }
+  }
+
+  endsWith(str: string): boolean {
+    return this._buf.endsWith(str);
+  }
+
+  removeTrailingNewline(): void {
+    this._buf.removeTrailingNewline();
+  }
+
+  source(prop: string, loc: Object): void {
+    this._catchUp(prop, loc);
+
+    this._buf.source(prop, loc);
+  }
+
+  withSource(prop: string, loc: Object, cb: () => void): void {
+    this._catchUp(prop, loc);
+
+    this._buf.withSource(prop, loc, cb);
+  }
+
+  _space(): void {
+    this._append(" ", true /* queue */);
+  }
+
+  _newline(): void {
+    this._append("\n", true /* queue */);
+  }
+
+  _append(str: string, queue: boolean = false) {
+    this._maybeAddParen(str);
+    this._maybeIndent(str);
+
+    if (queue) this._buf.queue(str);
+    else this._buf.append(str);
+
+    this._endsWithWord = false;
+  }
+
+  _maybeIndent(str: string): void {
+    // we've got a newline before us so prepend on the indentation
+    if (!this._format.compact && this._indent && this.endsWith("\n") && str[0] !== "\n") {
+      this._buf.queue(this._getIndent());
+    }
+  }
+
+  _maybeAddParen(str: string): void {
+    // see startTerminatorless() instance method
+    let parenPushNewlineState = this.parenPushNewlineState;
+    if (!parenPushNewlineState) return;
+    this.parenPushNewlineState = null;
+
+    let i;
+    for (i = 0; i < str.length && str[i] === " "; i++) continue;
+    if (i === str.length) return;
+
+    const cha = str[i];
+    if (cha === "\n" || cha === "/") {
+      // we're going to break this terminator expression so we need to add a parentheses
+      this.token("(");
+      this.indent();
+      parenPushNewlineState.printed = true;
+    }
+  }
+
+  _catchUp(prop: string, loc: Object) {
+    if (!this._format.retainLines) return;
+
+    // catch up to this nodes newline if we're behind
+    const pos = loc ? loc[prop] : null;
+    if (pos && pos.line !== null) {
+      while (this._buf.getCurrentLine() < pos.line) {
+        this._newline();
+      }
+    }
+  }
+
+  /**
+   * Set some state that will be modified if a newline has been inserted before any
+   * non-space characters.
+   *
+   * This is to prevent breaking semantics for terminatorless separator nodes. eg:
+   *
+   *    return foo;
+   *
+   * returns `foo`. But if we do:
+   *
+   *   return
+   *   foo;
+   *
+   *  `undefined` will be returned and not `foo` due to the terminator.
+   */
+
+  startTerminatorless(): Object {
+    return this.parenPushNewlineState = {
+      printed: false
+    };
+  }
+
+  /**
+   * Print an ending parentheses if a starting one has been printed.
+   */
+
+  endTerminatorless(state: Object) {
+    if (state.printed) {
+      this.dedent();
+      this.newline();
+      this.token(")");
+    }
   }
 
   print(node, parent, opts = {}) {
@@ -25,9 +270,9 @@ export default class Printer extends Buffer {
     let oldInAux = this.insideAux;
     this.insideAux = !node.loc;
 
-    let oldConcise = this.format.concise;
+    let oldConcise = this._format.concise;
     if (node._compact) {
-      this.format.concise = true;
+      this._format.concise = true;
     }
 
     let printMethod = this[node.type];
@@ -65,14 +310,14 @@ export default class Printer extends Buffer {
     this._printStack.pop();
     if (opts.after) opts.after();
 
-    this.format.concise = oldConcise;
+    this._format.concise = oldConcise;
     this.insideAux = oldInAux;
 
     this._printNewline(false, node, parent, opts);
   }
 
   printAuxBeforeComment(wasInAux) {
-    let comment = this.format.auxiliaryCommentBefore;
+    let comment = this._format.auxiliaryCommentBefore;
     if (!wasInAux && this.insideAux && !this.printAuxAfterOnNextUserNode) {
       this.printAuxAfterOnNextUserNode = true;
       if (comment) this.printComment({
@@ -85,7 +330,7 @@ export default class Printer extends Buffer {
   printAuxAfterComment() {
     if (this.printAuxAfterOnNextUserNode) {
       this.printAuxAfterOnNextUserNode = false;
-      let comment = this.format.auxiliaryCommentAfter;
+      let comment = this._format.auxiliaryCommentAfter;
       if (comment) this.printComment({
         type: "CommentBlock",
         value: comment
@@ -94,7 +339,7 @@ export default class Printer extends Buffer {
   }
 
   getPossibleRaw(node) {
-    if (this.format.minified) return;
+    if (this._format.minified) return;
 
     let extra = node.extra;
     if (extra && extra.raw != null && extra.rawValue != null && node.value === extra.rawValue) {
@@ -193,7 +438,7 @@ export default class Printer extends Buffer {
 
   _printNewline(leading, node, parent, opts) {
     // Fast path since 'this.newline' does nothing when not tracking lines.
-    if (this.format.retainLines || this.format.compact) return;
+    if (this._format.retainLines || this._format.compact) return;
 
     if (!opts.statement && !n.isUserWhitespacable(node, parent)) {
       return;
@@ -201,7 +446,7 @@ export default class Printer extends Buffer {
 
     // Fast path for concise since 'this.newline' just inserts a space when
     // concise formatting is in use.
-    if (this.format.concise) {
+    if (this._format.concise) {
       this.space();
       return;
     }
@@ -225,7 +470,7 @@ export default class Printer extends Buffer {
       if (needs(node, parent)) lines++;
 
       // generated nodes can't add starting file whitespace
-      if (!this.buf) lines = 0;
+      if (!this._buf.hasContent()) lines = 0;
     }
 
     this.newline(lines);
@@ -238,14 +483,14 @@ export default class Printer extends Buffer {
   }
 
   shouldPrintComment(comment) {
-    if (this.format.shouldPrintComment) {
-      return this.format.shouldPrintComment(comment.value);
+    if (this._format.shouldPrintComment) {
+      return this._format.shouldPrintComment(comment.value);
     } else {
-      if (!this.format.minified &&
+      if (!this._format.minified &&
           (comment.value.indexOf("@license") >= 0 || comment.value.indexOf("@preserve") >= 0)) {
         return true;
       } else {
-        return this.format.comments;
+        return this._format.comments;
       }
     }
   }
@@ -271,26 +516,26 @@ export default class Printer extends Buffer {
       let val    = this.generateComment(comment);
 
       //
-      if (comment.type === "CommentBlock" && this.format.indent.adjustMultilineComment) {
+      if (comment.type === "CommentBlock" && this._format.indent.adjustMultilineComment) {
         let offset = comment.loc && comment.loc.start.column;
         if (offset) {
           let newlineRegex = new RegExp("\\n\\s{1," + offset + "}", "g");
           val = val.replace(newlineRegex, "\n");
         }
 
-        let indent = Math.max(this.indentSize(), this.getCurrentColumn());
-        val = val.replace(/\n/g, `\n${repeat(" ", indent)}`);
+        let indentSize = Math.max(this._getIndent().length, this._buf.getCurrentColumn());
+        val = val.replace(/\n(?!$)/g, `\n${repeat(" ", indentSize)}`);
       }
 
       // force a newline for line comments when retainLines is set in case the next printed node
       // doesn't catch up
-      if ((this.format.compact || this.format.concise || this.format.retainLines) &&
+      if ((this._format.compact || this._format.concise || this._format.retainLines) &&
           comment.type === "CommentLine") {
         val += "\n";
       }
 
       //
-      this.push(val);
+      this.token(val);
 
       // whitespace after
       this.newline(this.whitespace.getNewlinesAfter(comment));

From 65a677decd3fb2f07d4b19baf8c0b7432348d16c Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Tue, 5 Jul 2016 20:05:33 -0700
Subject: [PATCH 12/12] Maintain a queue to allow deletion of
 whitespace/semicolons without accessing buf.

---
 packages/babel-generator/src/buffer.js | 78 +++++++++++++++++---------
 1 file changed, 51 insertions(+), 27 deletions(-)

diff --git a/packages/babel-generator/src/buffer.js b/packages/babel-generator/src/buffer.js
index 5bb911bbfc..10a0a9a0c1 100644
--- a/packages/babel-generator/src/buffer.js
+++ b/packages/babel-generator/src/buffer.js
@@ -2,6 +2,8 @@ import Position from "./position";
 import type SourceMap from "./source-map";
 import trimEnd from "lodash/trimEnd";
 
+const SPACES_RE = /^[ \t]+$/;
+
 /**
  * The Buffer class exists to manage the queue of tokens being pushed onto the output string
  * in such a way that the final string buffer is treated as write-only until the final .get()
@@ -31,6 +33,8 @@ export default class Buffer {
    */
 
   get(): Object {
+    this._flush();
+
     return {
       code: trimEnd(this._buf),
       map: this._map ? this._map.get() : null,
@@ -42,13 +46,9 @@ export default class Buffer {
    */
 
   append(str: string): void {
-    // If there the line is ending, adding a new mapping marker is redundant
-    if (this._map && str[0] !== "\n") this._map.mark(this._position, this._sourcePosition.line,
-      this._sourcePosition.column, this._sourcePosition.filename);
-
-    this._buf += str;
-    this._last = str[str.length - 1];
-    this._position.push(str);
+    this._flush();
+    this._append(str, this._sourcePosition.line, this._sourcePosition.column,
+      this._sourcePosition.filename);
   }
 
   /**
@@ -56,44 +56,58 @@ export default class Buffer {
    */
 
   queue(str: string): void {
-    this.append(str);
+    this._queue.unshift([str, this._sourcePosition.line, this._sourcePosition.column,
+      this._sourcePosition.filename]);
+  }
+
+  _flush(): void {
+    let item;
+    while (item = this._queue.pop()) this._append(...item);
+  }
+
+  _append(str: string, line: number, column: number, filename: ?string): void {
+    // If there the line is ending, adding a new mapping marker is redundant
+    if (this._map && str[0] !== "\n") this._map.mark(this._position, line, column, filename);
+
+    this._buf += str;
+    this._last = str[str.length - 1];
+    this._position.push(str);
   }
 
   removeTrailingSpaces(): void {
-    const oldBuf = this._buf;
-    this._buf = this._buf.replace(/[ \t]+$/, "");
-    this._last = this._buf[this._buf.length - 1];
-    this._position.unshift(oldBuf.slice(this._buf.length));
+    while (this._queue.length > 0 && SPACES_RE.test(this._queue[0][0])) this._queue.shift();
   }
 
   removeTrailingNewline(): void {
-    if (this._last !== "\n") return;
-
-    this._buf = this._buf.slice(0, -1);
-    this._last = this._buf[this._buf.length - 1];
-    this._position.unshift("\n");
+    if (this._queue.length > 0 && this._queue[0][0] === "\n") this._queue.shift();
   }
 
   removeLastSemicolon(): void {
-    if (this._last !== ";") return;
-
-    this._buf = this._buf.slice(0, -1);
-    this._last = this._buf[this._buf.length - 1];
-    this._position.unshift(";");
+    if (this._queue.length > 0 && this._queue[0][0] === ";") this._queue.shift();
   }
 
   endsWith(str: string): boolean {
-    if (str.length === 1) return str === this._last;
+    const end = this._last + this._queue.reduce((acc, item) => item[0] + acc, "");
+    if (str.length <= end.length) {
+      return end.slice(-str.length) === str;
+    }
 
-    return this._buf.slice(-str.length) === str;
+    // We assume that everything being matched is at most a single token plus some whitespace,
+    // which everything currently is, but otherwise we'd have to expand _last or check _buf.
+    return false;
   }
 
   getLast(): string {
+    if (this._queue.length > 0) {
+      const last = this._queue[this._queue.length - 1][0];
+      return last[last.length - 1];
+    }
+
     return this._last;
   }
 
   hasContent(): boolean {
-    return !!this._last;
+    return this._queue.length > 0 || !!this._last;
   }
 
   /**
@@ -133,10 +147,20 @@ export default class Buffer {
   }
 
   getCurrentColumn(): number {
-    return this._position.column;
+    const extra = this._queue.reduce((acc, item) => item[0] + acc, "");
+    const lastIndex = extra.lastIndexOf("\n");
+
+    return lastIndex === -1 ? this._position.column + extra.length : (extra.length - 1 - lastIndex);
   }
 
   getCurrentLine(): number {
-    return this._position.line;
+    const extra = this._queue.reduce((acc, item) => item[0] + acc, "");
+
+    let count = 0;
+    for (let i = 0; i < extra.length; i++) {
+      if (extra[i] === "\n") count++;
+    }
+
+    return this._position.line + count;
   }
 }