diff --git a/packages/babel-generator/src/buffer.js b/packages/babel-generator/src/buffer.js
index 14bd4d2e07..a1390c1762 100644
--- a/packages/babel-generator/src/buffer.js
+++ b/packages/babel-generator/src/buffer.js
@@ -58,6 +58,9 @@ export default class Buffer {
    */
 
   queue(str: string): void {
+    // Drop trailing spaces when a newline is inserted.
+    if (str === "\n") while (this._queue.length > 0 && SPACES_RE.test(this._queue[0][0])) this._queue.shift();
+
     const { line, column, filename } = this._sourcePosition;
     this._queue.unshift([str, line, column, filename]);
   }
@@ -86,10 +89,6 @@ export default class Buffer {
     }
   }
 
-  removeTrailingSpaces(): void {
-    while (this._queue.length > 0 && SPACES_RE.test(this._queue[0][0])) this._queue.shift();
-  }
-
   removeTrailingNewline(): void {
     if (this._queue.length > 0 && this._queue[0][0] === "\n") this._queue.shift();
   }
@@ -98,10 +97,23 @@ export default class Buffer {
     if (this._queue.length > 0 && this._queue[0][0] === ";") this._queue.shift();
   }
 
-  endsWith(str: string): boolean {
+  endsWith(suffix: string): boolean {
+    // Fast path to avoid iterating over this._queue.
+    if (suffix.length === 1) {
+      let last;
+      if (this._queue.length > 0) {
+        const str = this._queue[0][0];
+        last = str[str.length - 1];
+      } else {
+        last = this._last;
+      }
+
+      return last === suffix;
+    }
+
     const end = this._last + this._queue.reduce((acc, item) => item[0] + acc, "");
-    if (str.length <= end.length) {
-      return end.slice(-str.length) === str;
+    if (suffix.length <= end.length) {
+      return end.slice(-suffix.length) === suffix;
     }
 
     // We assume that everything being matched is at most a single token plus some whitespace,
@@ -109,15 +121,6 @@ export default class Buffer {
     return false;
   }
 
-  getLast(): string {
-    if (this._queue.length > 0) {
-      const last = this._queue[0][0];
-      return last[last.length - 1];
-    }
-
-    return this._last;
-  }
-
   hasContent(): boolean {
     return this._queue.length > 0 || !!this._last;
   }
diff --git a/packages/babel-generator/src/generators/base.js b/packages/babel-generator/src/generators/base.js
index bceaf00521..a7d1bd35b2 100644
--- a/packages/babel-generator/src/generators/base.js
+++ b/packages/babel-generator/src/generators/base.js
@@ -21,9 +21,12 @@ 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.removeTrailingNewline();
+    this.removeTrailingNewline();
 
     this.source("end", node.loc);
+
+    if (!this.endsWith("\n")) this.newline();
+
     this.rightBrace();
   } else {
     this.source("end", node.loc);
diff --git a/packages/babel-generator/src/generators/classes.js b/packages/babel-generator/src/generators/classes.js
index f7b75a321e..841473324a 100644
--- a/packages/babel-generator/src/generators/classes.js
+++ b/packages/babel-generator/src/generators/classes.js
@@ -42,6 +42,8 @@ export function ClassBody(node: Object) {
     this.printSequence(node.body, node);
     this.dedent();
 
+    if (!this.endsWith("\n")) this.newline();
+
     this.rightBrace();
   }
 }
diff --git a/packages/babel-generator/src/generators/expressions.js b/packages/babel-generator/src/generators/expressions.js
index 38f4973665..a6cc4548d0 100644
--- a/packages/babel-generator/src/generators/expressions.js
+++ b/packages/babel-generator/src/generators/expressions.js
@@ -1,13 +1,9 @@
 /* eslint max-len: 0 */
 
-import isInteger from "lodash/isInteger";
 import isNumber from "lodash/isNumber";
 import * as t from "babel-types";
 import * as n from "../node";
 
-const SCIENTIFIC_NOTATION = /e/i;
-const ZERO_DECIMAL_INTEGER = /\.0+$/;
-const NON_DECIMAL_LITERAL = /^0[box]/;
 
 export function UnaryExpression(node: Object) {
   if (node.operator === "void" || node.operator === "delete" || node.operator === "typeof") {
@@ -89,15 +85,16 @@ export function Decorator(node: Object) {
 function commaSeparatorNewline() {
   this.token(",");
   this.newline();
+
+  if (!this.endsWith("\n")) this.space();
 }
 
 export function CallExpression(node: Object) {
   this.print(node.callee, node);
-  if (node.loc) this.printAuxAfterComment();
 
   this.token("(");
 
-  let isPrettyCall = node._prettyCall && !this.format.retainLines && !this.format.compact;
+  let isPrettyCall = node._prettyCall;
 
   let separator;
   if (isPrettyCall) {
@@ -208,17 +205,6 @@ export function MemberExpression(node: Object) {
     this.print(node.property, node);
     this.token("]");
   } else {
-    if (t.isNumericLiteral(node.object)) {
-      let val = this.getPossibleRaw(node.object) || node.object.value;
-      if (isInteger(+val) &&
-        !NON_DECIMAL_LITERAL.test(val) &&
-        !SCIENTIFIC_NOTATION.test(val) &&
-        !ZERO_DECIMAL_INTEGER.test(val) &&
-        !this.endsWith(".")) {
-        this.token(".");
-      }
-    }
-
     this.token(".");
     this.print(node.property, node);
   }
diff --git a/packages/babel-generator/src/generators/flow.js b/packages/babel-generator/src/generators/flow.js
index eb4845ce1c..bd3748e51f 100644
--- a/packages/babel-generator/src/generators/flow.js
+++ b/packages/babel-generator/src/generators/flow.js
@@ -251,6 +251,7 @@ export function ObjectTypeAnnotation(node: Object) {
 
     this.printJoin(props, node, {
       indent: true,
+      statement: true,
       iterator: () => {
         if (props.length !== 1) {
           this.semicolon();
diff --git a/packages/babel-generator/src/generators/statements.js b/packages/babel-generator/src/generators/statements.js
index c3229db035..3a31ccc84d 100644
--- a/packages/babel-generator/src/generators/statements.js
+++ b/packages/babel-generator/src/generators/statements.js
@@ -1,7 +1,8 @@
 import * as t from "babel-types";
 
 export function WithStatement(node: Object) {
-  this.keyword("with");
+  this.word("with");
+  this.space();
   this.token("(");
   this.print(node.object, node);
   this.token(")");
@@ -9,7 +10,8 @@ export function WithStatement(node: Object) {
 }
 
 export function IfStatement(node: Object) {
-  this.keyword("if");
+  this.word("if");
+  this.space();
   this.token("(");
   this.print(node.test, node);
   this.token(")");
@@ -45,7 +47,8 @@ function getLastStatement(statement) {
 }
 
 export function ForStatement(node: Object) {
-  this.keyword("for");
+  this.word("for");
+  this.space();
   this.token("(");
 
   this.inForStatementInitCounter++;
@@ -69,7 +72,8 @@ export function ForStatement(node: Object) {
 }
 
 export function WhileStatement(node: Object) {
-  this.keyword("while");
+  this.word("while");
+  this.space();
   this.token("(");
   this.print(node.test, node);
   this.token(")");
@@ -78,7 +82,8 @@ export function WhileStatement(node: Object) {
 
 let buildForXStatement = function (op) {
   return function (node: Object) {
-    this.keyword("for");
+    this.word("for");
+    this.space();
     this.token("(");
     this.print(node.left, node);
     this.space();
@@ -98,7 +103,8 @@ export function DoWhileStatement(node: Object) {
   this.space();
   this.print(node.body, node);
   this.space();
-  this.keyword("while");
+  this.word("while");
+  this.space();
   this.token("(");
   this.print(node.test, node);
   this.token(")");
@@ -135,7 +141,8 @@ export function LabeledStatement(node: Object) {
 }
 
 export function TryStatement(node: Object) {
-  this.keyword("try");
+  this.word("try");
+  this.space();
   this.print(node.block, node);
   this.space();
 
@@ -157,7 +164,8 @@ export function TryStatement(node: Object) {
 }
 
 export function CatchClause(node: Object) {
-  this.keyword("catch");
+  this.word("catch");
+  this.space();
   this.token("(");
   this.print(node.param, node);
   this.token(")");
@@ -166,7 +174,8 @@ export function CatchClause(node: Object) {
 }
 
 export function SwitchStatement(node: Object) {
-  this.keyword("switch");
+  this.word("switch");
+  this.space();
   this.token("(");
   this.print(node.discriminant, node);
   this.token(")");
@@ -209,14 +218,14 @@ function variableDeclarationIdent() {
   // "let " or "var " indentation.
   this.token(",");
   this.newline();
-  for (let i = 0; i < 4; i++) this.space(true);
+  if (this.endsWith("\n")) 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.space(true);
+  if (this.endsWith("\n")) for (let i = 0; i < 6; i++) this.space(true);
 }
 
 export function VariableDeclaration(node: Object, parent: Object) {
@@ -247,7 +256,7 @@ export function VariableDeclaration(node: Object, parent: Object) {
   //
 
   let separator;
-  if (!this.format.compact && !this.format.concise && hasInits && !this.format.retainLines) {
+  if (hasInits) {
     separator = node.kind === "const" ? constDeclarationIdent : variableDeclarationIdent;
   }
 
diff --git a/packages/babel-generator/src/generators/types.js b/packages/babel-generator/src/generators/types.js
index ccca3ba6dc..9d7ecde738 100644
--- a/packages/babel-generator/src/generators/types.js
+++ b/packages/babel-generator/src/generators/types.js
@@ -38,7 +38,7 @@ export function ObjectExpression(node: Object) {
 
   if (props.length) {
     this.space();
-    this.printList(props, node, { indent: true });
+    this.printList(props, node, { indent: true, statement: true });
     this.space();
   }
 
@@ -124,12 +124,8 @@ export function NullLiteral() {
 
 export function NumericLiteral(node: Object) {
   let raw = this.getPossibleRaw(node);
-  if (raw != null) {
-    this.word(raw);
-    return;
-  }
 
-  this.word(node.value + "");
+  this.number(raw == null ? node.value + "" : raw);
 }
 
 export function StringLiteral(node: Object, parent: Object) {
diff --git a/packages/babel-generator/src/index.js b/packages/babel-generator/src/index.js
index f660233c6e..5b106a401b 100644
--- a/packages/babel-generator/src/index.js
+++ b/packages/babel-generator/src/index.js
@@ -1,8 +1,8 @@
 import detectIndent from "detect-indent";
-import Whitespace from "./whitespace";
 import SourceMap from "./source-map";
 import * as messages from "babel-messages";
 import Printer from "./printer";
+import type {Format} from "./printer";
 
 /**
  * Babel's code generator, turns an ast into code, maintaining sourcemaps,
@@ -14,119 +14,15 @@ class Generator extends Printer {
     opts = opts || {};
 
     const tokens = ast.tokens || [];
-    let format   = Generator.normalizeOptions(code, opts, tokens);
+    let format = normalizeOptions(code, opts, tokens);
+    let map = opts.sourceMaps ? new SourceMap(opts, code) : null;
+    super(format, map, tokens);
 
-    let map        = opts.sourceMaps ? new SourceMap(opts, code) : null;
-
-    super(format, map);
-
-    this.ast      = ast;
-
-    this._whitespace = tokens.length > 0 ? new Whitespace(tokens) : null;
+    this.ast = ast;
   }
 
-  format: {
-    shouldPrintComment: (comment: string) => boolean;
-    retainLines: boolean;
-    comments: boolean;
-    auxiliaryCommentBefore: string;
-    auxiliaryCommentAfter: string;
-    compact: boolean | "auto";
-    minified: boolean;
-    quotes: "single" | "double";
-    concise: boolean;
-    indent: {
-      adjustMultilineComment: boolean;
-      style: string;
-      base: number;
-    }
-  };
-
-  _whitespace: Whitespace;
   ast: Object;
 
-  /**
-   * Normalize generator options, setting defaults.
-   *
-   * - Detects code indentation.
-   * - If `opts.compact = "auto"` and the code is over 100KB, `compact` will be set to `true`.
-   */
-
-  static normalizeOptions(code, opts, tokens) {
-    let style = "  ";
-    if (code && typeof code === "string") {
-      let indent = detectIndent(code).indent;
-      if (indent && indent !== " ") style = indent;
-    }
-
-    let format = {
-      auxiliaryCommentBefore: opts.auxiliaryCommentBefore,
-      auxiliaryCommentAfter: opts.auxiliaryCommentAfter,
-      shouldPrintComment: opts.shouldPrintComment,
-      retainLines: opts.retainLines,
-      comments: opts.comments == null || opts.comments,
-      compact: opts.compact,
-      minified: opts.minified,
-      concise: opts.concise,
-      quotes: opts.quotes || Generator.findCommonStringDelimiter(code, tokens),
-      indent: {
-        adjustMultilineComment: true,
-        style: style,
-        base: 0
-      }
-    };
-
-    if (format.minified) {
-      format.compact = true;
-    }
-
-    if (format.compact === "auto") {
-      format.compact = code.length > 100000; // 100KB
-
-      if (format.compact) {
-        console.error("[BABEL] " + messages.get("codeGeneratorDeopt", opts.filename, "100KB"));
-      }
-    }
-
-    if (format.compact) {
-      format.indent.adjustMultilineComment = false;
-    }
-
-    return format;
-  }
-
-  /**
-   * Determine if input code uses more single or double quotes.
-   */
-  static findCommonStringDelimiter(code, tokens) {
-    let occurences = {
-      single: 0,
-      double: 0
-    };
-
-    let checked = 0;
-
-    for (let i = 0; i < tokens.length; i++) {
-      let token = tokens[i];
-      if (token.type.label !== "string") continue;
-
-      let raw = code.slice(token.start, token.end);
-      if (raw[0] === "'") {
-        occurences.single++;
-      } else {
-        occurences.double++;
-      }
-
-      checked++;
-      if (checked >= 3) break;
-    }
-    if (occurences.single > occurences.double) {
-      return "single";
-    } else {
-      return "double";
-    }
-  }
-
   /**
    * Generate code and sourcemap from ast.
    *
@@ -134,13 +30,96 @@ class Generator extends Printer {
    */
 
   generate() {
-    this.print(this.ast);
-    this.printAuxAfterComment();
-
-    return this._buf.get();
+    return super.generate(this.ast);
   }
 }
 
+/**
+ * Normalize generator options, setting defaults.
+ *
+ * - Detects code indentation.
+ * - If `opts.compact = "auto"` and the code is over 100KB, `compact` will be set to `true`.
+ */
+
+function normalizeOptions(code, opts, tokens): Format {
+  let style = "  ";
+  if (code && typeof code === "string") {
+    let indent = detectIndent(code).indent;
+    if (indent && indent !== " ") style = indent;
+  }
+
+  let format = {
+    auxiliaryCommentBefore: opts.auxiliaryCommentBefore,
+    auxiliaryCommentAfter: opts.auxiliaryCommentAfter,
+    shouldPrintComment: opts.shouldPrintComment,
+    retainLines: opts.retainLines,
+    comments: opts.comments == null || opts.comments,
+    compact: opts.compact,
+    minified: opts.minified,
+    concise: opts.concise,
+    quotes: opts.quotes || findCommonStringDelimiter(code, tokens),
+    indent: {
+      adjustMultilineComment: true,
+      style: style,
+      base: 0
+    }
+  };
+
+  if (format.minified) {
+    format.compact = true;
+
+    format.shouldPrintComment = format.shouldPrintComment || (() => format.comments);
+  } else {
+    format.shouldPrintComment = format.shouldPrintComment || ((value) => format.comments ||
+      (value.indexOf("@license") >= 0 || value.indexOf("@preserve") >= 0));
+  }
+
+  if (format.compact === "auto") {
+    format.compact = code.length > 100000; // 100KB
+
+    if (format.compact) {
+      console.error("[BABEL] " + messages.get("codeGeneratorDeopt", opts.filename, "100KB"));
+    }
+  }
+
+  if (format.compact) {
+    format.indent.adjustMultilineComment = false;
+  }
+
+  return format;
+}
+
+/**
+ * Determine if input code uses more single or double quotes.
+ */
+function findCommonStringDelimiter(code, tokens) {
+  let occurences = {
+    single: 0,
+    double: 0
+  };
+
+  let checked = 0;
+
+  for (let i = 0; i < tokens.length; i++) {
+    let token = tokens[i];
+    if (token.type.label !== "string") continue;
+
+    let raw = code.slice(token.start, token.end);
+    if (raw[0] === "'") {
+      occurences.single++;
+    } else {
+      occurences.double++;
+    }
+
+    checked++;
+    if (checked >= 3) break;
+  }
+  if (occurences.single > occurences.double) {
+    return "single";
+  } else {
+    return "double";
+  }
+}
 
 /**
  * We originally exported the Generator class above, but to make it extra clear that it is a private API,
diff --git a/packages/babel-generator/src/node/index.js b/packages/babel-generator/src/node/index.js
index 4f1d48c42b..971f478a3d 100644
--- a/packages/babel-generator/src/node/index.js
+++ b/packages/babel-generator/src/node/index.js
@@ -53,11 +53,6 @@ function isOrHasCallExpression(node) {
   }
 }
 
-
-export function isUserWhitespacable(node) {
-  return t.isUserWhitespacable(node);
-}
-
 export function needsWhitespace(node, parent, type) {
   if (!node) return 0;
 
diff --git a/packages/babel-generator/src/printer.js b/packages/babel-generator/src/printer.js
index 6ecd82530d..fea799595f 100644
--- a/packages/babel-generator/src/printer.js
+++ b/packages/babel-generator/src/printer.js
@@ -1,25 +1,63 @@
 /* eslint max-len: 0 */
 
+import find from "lodash/find";
+import findLast from "lodash/findLast";
+import isInteger from "lodash/isInteger";
 import repeat from "lodash/repeat";
 import Buffer from "./buffer";
 import * as n from "./node";
+import Whitespace from "./whitespace";
 import * as t from "babel-types";
 
+const SCIENTIFIC_NOTATION = /e/i;
+const ZERO_DECIMAL_INTEGER = /\.0+$/;
+const NON_DECIMAL_LITERAL = /^0[box]/;
+
+export type Format = {
+  shouldPrintComment: (comment: string) => boolean;
+  retainLines: boolean;
+  comments: boolean;
+  auxiliaryCommentBefore: string;
+  auxiliaryCommentAfter: string;
+  compact: boolean | "auto";
+  minified: boolean;
+  quotes: "single" | "double";
+  concise: boolean;
+  indent: {
+    adjustMultilineComment: boolean;
+    style: string;
+    base: number;
+  }
+};
+
 export default class Printer {
-  constructor(format, map) {
+  constructor(format, map, tokens) {
     this.format = format || {};
     this._buf = new Buffer(map);
-    this.insideAux = false;
-    this._printAuxAfterOnNextUserNode = false;
-    this._printStack = [];
-    this._printedCommentStarts = {};
-    this._parenPushNewlineState = null;
-    this._indent = 0;
-    this.inForStatementInitCounter = 0;
+    this._whitespace = tokens.length > 0 ? new Whitespace(tokens) : null;
   }
 
-  _printedCommentStarts: Object;
-  _parenPushNewlineState: ?Object;
+  format: Format;
+  inForStatementInitCounter: number = 0;
+
+  _buf: Buffer;
+  _whitespace: Whitespace;
+  _printStack: Array<Node> = [];
+  _indent: number = 0;
+  _insideAux: boolean = false;
+  _printedCommentStarts: Object = {};
+  _parenPushNewlineState: ?Object = null;
+  _printAuxAfterOnNextUserNode: boolean = false;
+  _printedComments: WeakSet = new WeakSet();
+  _endsWithInteger = false;
+  _endsWithWord = false;
+
+  generate(ast) {
+    this.print(ast);
+    this._maybeAddAuxComment();
+
+    return this._buf.get();
+  }
 
   /**
    * Increment indent size.
@@ -46,6 +84,7 @@ export default class Printer {
    */
 
   semicolon(force: boolean = false): void {
+    this._maybeAddAuxComment();
     this._append(";", !force /* queue */);
   }
 
@@ -54,23 +93,12 @@ export default class Printer {
    */
 
   rightBrace(): void {
-    if (!this.endsWith("\n")) this.newline();
-
     if (this.format.minified) {
       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.
    */
@@ -90,27 +118,48 @@ export default class Printer {
   word(str: string): void {
     if (this._endsWithWord) this._space();
 
+    this._maybeAddAuxComment();
     this._append(str);
 
     this._endsWithWord = true;
   }
 
+  /**
+   * Writes a number token so that we can validate if it is an integer.
+   */
+
+  number(str: string): void {
+    this.word(str);
+
+    // Integer tokens need special handling because they cannot have '.'s inserted
+    // immediately after them.
+    this._endsWithInteger =
+      isInteger(+str) &&
+      !NON_DECIMAL_LITERAL.test(str) &&
+      !SCIENTIFIC_NOTATION.test(str) &&
+      !ZERO_DECIMAL_INTEGER.test(str) &&
+      str[str.length - 1] !== ".";
+  }
+
   /**
    * 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 === "!") ||
+    if ((str === "--" && this.endsWith("!")) ||
 
       // Need spaces for operators of the same kind to avoid: `a+++b`
-      (str[0] === "+" && last === "+") ||
-      (str[0] === "-" && last === "-")) {
+      (str[0] === "+" && this.endsWith("+")) ||
+      (str[0] === "-" && this.endsWith("-")) ||
+
+      // Needs spaces to avoid changing '34' to '34.', which would still be a valid number.
+      (str[0] === "." && this._endsWithInteger)) {
       this._space();
     }
 
+    this._maybeAddAuxComment();
     this._append(str);
   }
 
@@ -135,7 +184,6 @@ export default class Printer {
     if (this.endsWith("{\n") || this.endsWith(":\n")) i--;
     if (i <= 0) return;
 
-    this._buf.removeTrailingSpaces();
     for (let j = 0; j < i; j++) {
       this._newline();
     }
@@ -177,6 +225,7 @@ export default class Printer {
     else this._buf.append(str);
 
     this._endsWithWord = false;
+    this._endsWithInteger = false;
   }
 
   _maybeIndent(str: string): void {
@@ -211,7 +260,9 @@ export default class Printer {
     // 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) {
+      const count = pos.line - this._buf.getCurrentLine();
+
+      for (let i = 0; i < count; i++) {
         this._newline();
       }
     }
@@ -259,7 +310,7 @@ export default class Printer {
     }
   }
 
-  print(node, parent, opts = {}) {
+  print(node, parent) {
     if (!node) return;
 
     let oldConcise = this.format.concise;
@@ -274,38 +325,34 @@ export default class Printer {
 
     this._printStack.push(node);
 
-    let oldInAux = this.insideAux;
-    this.insideAux = !node.loc;
-    if (!this.insideAux) this.printAuxAfterComment();
-    else if (!oldInAux) this._printAuxBeforeComment();
+    let oldInAux = this._insideAux;
+    this._insideAux = !node.loc;
+    this._maybeAddAuxComment(this._insideAux && !oldInAux);
 
     let needsParens = n.needsParens(node, parent, this._printStack);
     if (needsParens) this.token("(");
 
     this._printLeadingComments(node, parent);
 
-    this._printNewline(true, node, parent, opts);
-
     let loc = (t.isProgram(node) || t.isFile(node)) ? null : node.loc;
     this.withSource("start", loc, () => {
       this[node.type](node, parent);
     });
 
-    // Check again if any of our children may have left an aux comment on the stack
-    if (!this.insideAux) this.printAuxAfterComment();
-
     this._printTrailingComments(node, parent);
 
     if (needsParens) this.token(")");
 
     // end
     this._printStack.pop();
-    if (opts.after) opts.after();
 
     this.format.concise = oldConcise;
-    this.insideAux = oldInAux;
+    this._insideAux = oldInAux;
+  }
 
-    this._printNewline(false, node, parent, opts);
+  _maybeAddAuxComment(enteredPositionlessNode) {
+    if (enteredPositionlessNode) this._printAuxBeforeComment();
+    if (!this._insideAux) this._printAuxAfterComment();
   }
 
   _printAuxBeforeComment() {
@@ -321,7 +368,7 @@ export default class Printer {
     }
   }
 
-  printAuxAfterComment() {
+  _printAuxAfterComment() {
     if (!this._printAuxAfterOnNextUserNode) return;
     this._printAuxAfterOnNextUserNode = false;
 
@@ -346,32 +393,29 @@ export default class Printer {
   printJoin(nodes: ?Array, parent: Object, opts = {}) {
     if (!nodes || !nodes.length) return;
 
-    let len = nodes.length;
-    let node, i;
-
     if (opts.indent) this.indent();
 
-    let printOpts = {
-      statement: opts.statement,
+    const newlineOpts = {
       addNewlines: opts.addNewlines,
-      after: () => {
-        if (opts.iterator) {
-          opts.iterator(node, i);
-        }
-
-        if (opts.separator && parent.loc) {
-          this.printAuxAfterComment();
-        }
-
-        if (opts.separator && i < len - 1) {
-          opts.separator.call(this);
-        }
-      }
     };
 
-    for (i = 0; i < nodes.length; i++) {
-      node = nodes[i];
-      this.print(node, parent, printOpts);
+    for (let i = 0; i < nodes.length; i++) {
+      const node = nodes[i];
+      if (!node) continue;
+
+      if (opts.statement) this._printNewline(true, node, parent, newlineOpts);
+
+      this.print(node, parent);
+
+      if (opts.iterator) {
+        opts.iterator(node, i);
+      }
+
+      if (opts.separator && i < nodes.length - 1) {
+        opts.separator.call(this);
+      }
+
+      if (opts.statement) this._printNewline(false, node, parent, newlineOpts);
     }
 
     if (opts.indent) this.dedent();
@@ -426,10 +470,6 @@ export default class Printer {
     // Fast path since 'this.newline' does nothing when not tracking lines.
     if (this.format.retainLines || this.format.compact) return;
 
-    if (!opts.statement && !n.isUserWhitespacable(node, parent)) {
-      return;
-    }
-
     // Fast path for concise since 'this.newline' just inserts a space when
     // concise formatting is in use.
     if (this.format.concise) {
@@ -442,9 +482,17 @@ export default class Printer {
     if (node.start != null && !node._ignoreUserWhitespace && this._whitespace) {
       // user node
       if (leading) {
-        lines = this._whitespace.getNewlinesBefore(node);
+        const comments = node.leadingComments;
+        const comment = comments && find(comments, (comment) =>
+          !!comment.loc && this.format.shouldPrintComment(comment.value));
+
+        lines = this._whitespace.getNewlinesBefore(comment || node);
       } else {
-        lines = this._whitespace.getNewlinesAfter(node);
+        const comments = node.trailingComments;
+        const comment = comments && findLast(comments, (comment) =>
+          !!comment.loc && this.format.shouldPrintComment(comment.value));
+
+        lines = this._whitespace.getNewlinesAfter(comment || node);
       }
     } else {
       // generated node
@@ -468,65 +516,48 @@ export default class Printer {
     return (node && (leading ? node.leadingComments : node.trailingComments)) || [];
   }
 
-  _shouldPrintComment(comment) {
-    if (this.format.shouldPrintComment) {
-      return this.format.shouldPrintComment(comment.value);
-    } else {
-      if (!this.format.minified &&
-          (comment.value.indexOf("@license") >= 0 || comment.value.indexOf("@preserve") >= 0)) {
-        return true;
-      } else {
-        return this.format.comments;
-      }
-    }
-  }
-
   _printComment(comment) {
-    if (!this._shouldPrintComment(comment)) return;
+    if (!this.format.shouldPrintComment(comment.value)) return;
 
+    // Some plugins use this to mark comments as removed using the AST-root 'comments' property,
+    // where they can't manually mutate the AST node comment lists.
     if (comment.ignore) return;
-    comment.ignore = true;
+
+    if (this._printedComments.has(comment)) return;
+    this._printedComments.add(comment);
 
     if (comment.start != null) {
       if (this._printedCommentStarts[comment.start]) return;
       this._printedCommentStarts[comment.start] = true;
     }
 
-    // Exclude comments from source mappings since they will only clutter things.
+    // whitespace before
+    this.newline(this._whitespace ? this._whitespace.getNewlinesBefore(comment) : 0);
+
+    if (!this.endsWith("[") && !this.endsWith("{")) this.space();
+
+    let val = comment.type === "CommentLine" ? `//${comment.value}\n` : `/*${comment.value}*/`;
+
+    //
+    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 indentSize = Math.max(this._getIndent().length, this._buf.getCurrentColumn());
+      val = val.replace(/\n(?!$)/g, `\n${repeat(" ", indentSize)}`);
+    }
+
     this.withSource("start", comment.loc, () => {
-      // whitespace before
-      this.newline(this._whitespace ? this._whitespace.getNewlinesBefore(comment) : 0);
-
-      if (!this.endsWith("[") && !this.endsWith("{")) this.space();
-
-      let val = comment.type === "CommentLine" ? `//${comment.value}` : `/*${comment.value}*/`;
-
-      //
-      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 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) &&
-          comment.type === "CommentLine") {
-        val += "\n";
-      }
-
-      //
-      this.token(val);
-
-      // whitespace after
-      this.newline((this._whitespace ? this._whitespace.getNewlinesAfter(comment) : 0) ||
-        (comment.type === "CommentLine" ? 1 : 0));
+      this._append(val);
     });
+
+    // whitespace after
+    this.newline((this._whitespace ? this._whitespace.getNewlinesAfter(comment) : 0) +
+      // Subtract one to account for the line force-added above.
+      (comment.type === "CommentLine" ? -1 : 0));
   }
 
   _printComments(comments?: Array<Object>) {
diff --git a/packages/babel-generator/test/fixtures/comments/simple-a-lot-of-line-comment/expected.js b/packages/babel-generator/test/fixtures/comments/simple-a-lot-of-line-comment/expected.js
index 47869b2606..45443e8c59 100644
--- a/packages/babel-generator/test/fixtures/comments/simple-a-lot-of-line-comment/expected.js
+++ b/packages/babel-generator/test/fixtures/comments/simple-a-lot-of-line-comment/expected.js
@@ -20,6 +20,7 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 // THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+
 function test() {}
 
 // Copyright (C) 2012 Yusuke Suzuki <utatane.tea@gmail.com>
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 fd1cba7b14..809ec9aa05 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
@@ -6,6 +6,6 @@ function foo(l) {
 
 function foo() {
   return (
-    1 && 2 || 
+    1 && 2 ||
     3);
 }
diff --git a/packages/babel-generator/test/fixtures/parentheses/terminator-break/expected.js b/packages/babel-generator/test/fixtures/parentheses/terminator-break/expected.js
index e6604a1cf0..750b0e8c70 100644
--- a/packages/babel-generator/test/fixtures/parentheses/terminator-break/expected.js
+++ b/packages/babel-generator/test/fixtures/parentheses/terminator-break/expected.js
@@ -5,7 +5,7 @@ function foo() {
 }
 
 function foo() {
-  return(
+  return (
     // foobar
     "bar"
   );
diff --git a/packages/babel-plugin-transform-es2015-modules-commonjs/test/fixtures/auxiliary-comment/overview/expected.js b/packages/babel-plugin-transform-es2015-modules-commonjs/test/fixtures/auxiliary-comment/overview/expected.js
index 10c5029307..3ea207e748 100644
--- a/packages/babel-plugin-transform-es2015-modules-commonjs/test/fixtures/auxiliary-comment/overview/expected.js
+++ b/packages/babel-plugin-transform-es2015-modules-commonjs/test/fixtures/auxiliary-comment/overview/expected.js
@@ -4,20 +4,18 @@ Object.defineProperty(exports, "__esModule", {
   value: true
 });
 exports.test = undefined;
-/*after*/
-/*before*/require("foo"); /*after*/
 
-/*before*/require("foo-bar"); /*after*/
+/*after*/ /*before*/require("foo") /*after*/;
 
-/*before*/require("./directory/foo-bar"); /*after*/
+/*before*/require("foo-bar") /*after*/;
+
+/*before*/require("./directory/foo-bar") /*after*/;
 
 var /*before*/_foo = require("foo2") /*after*/;
 
-/*before*/
-var _foo2 = babelHelpers.interopRequireDefault(_foo);
+/*before*/var _foo2 = babelHelpers.interopRequireDefault(_foo);
 
-/*after*/
-var /*before*/_foo3 = require("foo3") /*after*/;
+/*after*/var /*before*/_foo3 = require("foo3") /*after*/;
 
 /*before*/var /*after*/foo2 = babelHelpers.interopRequireWildcard(_foo3);
 
@@ -31,5 +29,5 @@ var test = /*before*/exports. /*after*/test = 5;
 /*before*/(0, _foo4.bar) /*after*/( /*before*/_foo2.default /*after*/, /*before*/_foo5.foo /*after*/);
 
 /* my comment */
-/*before*/_foo5.foo; /*after*/
-/*before*/_foo2.default; /*after*/
+/*before*/_foo5.foo /*after*/;
+/*before*/_foo2.default /*after*/;