Add decimal parsing support (#11640)

* docs: add DecimalLiteral to AST spec

* add decimal support

* fix: throw invalid decimal on start

* add DecimalLiteral type definitions

* update parser typings

* add generator support

* add syntax-decimal plugin

* Add syntax-decimal to babel-standalone

* add syntax-decimal to missing plugin helpers

* fix incorrect test macro

packages/babel-parser/src/tokenizer/index.js

@@ -1095,6 +1095,8 @@ export default class Tokenizer extends ParserErrors {
     if (next === charCodes.lowercaseN) {
       ++this.state.pos;
       isBigInt = true;
+    } else if (next === charCodes.lowercaseM) {
+      throw this.raise(start, Errors.InvalidDecimal);
     }
 
     if (isIdentifierStart(this.input.codePointAt(this.state.pos))) {
@@ -1116,6 +1118,8 @@ export default class Tokenizer extends ParserErrors {
     const start = this.state.pos;
     let isFloat = false;
     let isBigInt = false;
+    let isDecimal = false;
+    let hasExponent = false;
     let isOctal = false;
 
     if (!startsWithDot && this.readInt(10) === null) {
@@ -1157,6 +1161,7 @@ export default class Tokenizer extends ParserErrors {
       }
       if (this.readInt(10) === null) this.raise(start, Errors.InvalidNumber);
       isFloat = true;
+      hasExponent = true;
       next = this.input.charCodeAt(this.state.pos);
     }
 
@@ -1174,18 +1179,32 @@ export default class Tokenizer extends ParserErrors {
       isBigInt = true;
     }
 
+    if (next === charCodes.lowercaseM) {
+      this.expectPlugin("decimal", this.state.pos);
+      if (hasExponent || hasLeadingZero) {
+        this.raise(start, Errors.InvalidDecimal);
+      }
+      ++this.state.pos;
+      isDecimal = true;
+    }
+
     if (isIdentifierStart(this.input.codePointAt(this.state.pos))) {
       throw this.raise(this.state.pos, Errors.NumberIdentifier);
     }
 
-    // remove "_" for numeric literal separator, and "n" for BigInts
-    const str = this.input.slice(start, this.state.pos).replace(/[_n]/g, "");
+    // remove "_" for numeric literal separator, and trailing `m` or `n`
+    const str = this.input.slice(start, this.state.pos).replace(/[_mn]/g, "");
 
     if (isBigInt) {
       this.finishToken(tt.bigint, str);
       return;
     }
 
+    if (isDecimal) {
+      this.finishToken(tt.decimal, str);
+      return;
+    }
+
     const val = isOctal ? parseInt(str, 8) : parseFloat(str);
     this.finishToken(tt.num, val);
   }

packages/babel-parser/src/tokenizer/types.js

@@ -86,6 +86,7 @@ function createBinop(name: string, binop: number) {
 export const types: { [name: string]: TokenType } = {
   num: new TokenType("num", { startsExpr }),
   bigint: new TokenType("bigint", { startsExpr }),
+  decimal: new TokenType("decimal", { startsExpr }),
   regexp: new TokenType("regexp", { startsExpr }),
   string: new TokenType("string", { startsExpr }),
   name: new TokenType("name", { startsExpr }),