Perform number decimal checks at the token level.

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") {
@@ -209,17 +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);
   }

packages/babel-generator/src/generators/types.js

@@ -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) {

packages/babel-generator/src/printer.js

@@ -2,12 +2,17 @@
 
 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;
@@ -44,6 +49,8 @@ export default class Printer {
   _parenPushNewlineState: ?Object = null;
   _printAuxAfterOnNextUserNode: boolean = false;
   _printedComments: WeakSet = new WeakSet();
+  _endsWithInteger = false;
+  _endsWithWord = false;
 
   generate(ast) {
     this.print(ast);
@@ -126,6 +133,23 @@ export default class Printer {
     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.
    */
@@ -137,7 +161,10 @@ export default class Printer {
 
       // Need spaces for operators of the same kind to avoid: `a+++b`
       (str[0] === "+" && this.endsWith("+")) ||
-      (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();
     }
 
@@ -207,6 +234,7 @@ export default class Printer {
     else this._buf.append(str);
 
     this._endsWithWord = false;
+    this._endsWithInteger = false;
   }
 
   _maybeIndent(str: string): void {