Track sourcemap location on a stack - fixes T7255

packages/babel-generator/src/buffer.js

@@ -19,6 +19,13 @@ export default class Buffer {
     // 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,
+    };
   }
 
   printedCommentStarts: Object;
@@ -230,6 +237,40 @@ export default class Buffer {
     }
   }
 
+  /**
+   * Sets a given position as the current source location so generated code after this call
+   * will be given this position in the sourcemap.
+   */
+
+  source(prop: string, loc: Location) {
+    if (prop && !loc) return;
+
+    let pos = loc ? loc[prop] : null;
+
+    this._sourcePosition.line = pos ? pos.line : null;
+    this._sourcePosition.column = pos ? pos.column : null;
+    this._sourcePosition.filename = loc && loc.filename || null;
+  }
+
+  /**
+   * Call a callback with a specific source location and restore on completion.
+   */
+
+  withSource(prop: string, loc: Location, cb: () => void) {
+    // Use the call stack to manage a stack of "source location" data.
+    let originalLine = this._sourcePosition.line;
+    let originalColumn = this._sourcePosition.column;
+    let originalFilename = this._sourcePosition.filename;
+
+    this.source(prop, loc);
+
+    cb();
+
+    this._sourcePosition.line = originalLine;
+    this._sourcePosition.column = originalColumn;
+    this._sourcePosition.filename = originalFilename;
+  }
+
   /**
    * Push a string to the buffer, maintaining indentation and newlines.
    */
@@ -276,6 +317,9 @@ export default class Buffer {
       }
     }
 
+    // If there the line is ending, adding a new mapping marker is redundant
+    if (str[0] !== "\n") this.map.mark(this._sourcePosition);
+
     //
     this.position.push(str);
     this.buf += str;

packages/babel-generator/src/printer.js

@@ -51,9 +51,10 @@ export default class Printer extends Buffer {
 
     if (opts.before) opts.before();
 
-    this.map.mark(node);
-
-    this._print(node, parent);
+    let loc = (t.isProgram(node) || t.isFile(node)) ? null : node.loc;
+    this.withSource("start", loc, () => {
+      this._print(node, parent);
+    });
 
     // Check again if any of our children may have left an aux comment on the stack
     if (node.loc) this.printAuxAfterComment();
@@ -64,7 +65,6 @@ export default class Printer extends Buffer {
 
     // end
     this._printStack.pop();
-    if (parent) this.map.mark(parent);
     if (opts.after) opts.after();
 
     this.format.concise = oldConcise;
@@ -268,46 +268,50 @@ export default class Printer extends Buffer {
       this.printedCommentStarts[comment.start] = true;
     }
 
-    this.catchUp(comment);
+    // Exclude comments from source mappings since they will only clutter things.
+    this.withSource(null, null, () => {
+      this.catchUp(comment);
 
-    // whitespace before
-    this.newline(this.whitespace.getNewlinesBefore(comment));
+      // whitespace before
+      this.newline(this.whitespace.getNewlinesBefore(comment));
 
-    let column = this.position.column;
-    let val    = this.generateComment(comment);
+      let column = this.position.column;
+      let val    = this.generateComment(comment);
 
-    if (column && !this.isLast(["\n", " ", "[", "{"])) {
-      this._push(" ");
-      column++;
-    }
-
-    //
-    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");
+      if (column && !this.isLast(["\n", " ", "[", "{"])) {
+        this._push(" ");
+        column++;
       }
 
-      let indent = Math.max(this.indentSize(), column);
-      val = val.replace(/\n/g, `\n${repeating(" ", indent)}`);
-    }
+      //
+      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");
+        }
 
-    if (column === 0) {
-      val = this.getIndent() + val;
-    }
+        let indent = Math.max(this.indentSize(), column);
+        val = val.replace(/\n/g, `\n${repeating(" ", indent)}`);
+      }
 
-    // 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";
-    }
+      if (column === 0) {
+        val = this.getIndent() + val;
+      }
 
-    //
-    this._push(val);
+      // 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";
+      }
 
-    // whitespace after
-    this.newline(this.whitespace.getNewlinesAfter(comment));
+      //
+      this._push(val);
+
+      // whitespace after
+      this.newline(this.whitespace.getNewlinesAfter(comment));
+    });
   }
 
   printComments(comments?: Array<Object>) {

packages/babel-generator/src/source-map.js

@@ -1,5 +1,4 @@
 import sourceMap from "source-map";
-import * as t from "babel-types";
 
 /**
  * Build a sourcemap.
@@ -43,46 +42,40 @@ export default class SourceMap {
   }
 
   /**
-   * Mark a node's generated position, and add it to the sourcemap.
+   * Mark the current generated position with a source position. May also be passed null line/column
+   * values to insert a mapping to nothing.
    */
 
-  mark(node) {
-    let loc = node.loc;
-    if (!loc) return; // no location info
-
+  mark(sourcePos: Object) {
     let map = this.map;
     if (!map) return; // no source map
 
-    if (t.isProgram(node) || t.isFile(node)) return; // illegal mapping nodes
-
     let position = this.position;
 
-    let generated = {
-      line: position.line,
-      column: position.column
-    };
+    // Adding an empty mapping at the start of a generated line just clutters the map.
+    if (this._lastGenLine !== position.line && sourcePos.line === null) return;
 
-    let original = loc.start;
-
-    // Avoid emitting duplicates on either side. Duplicated
-    // original values creates unnecesssarily large source maps
-    // and increases compile time. Duplicates on the generated
-    // side can lead to incorrect mappings.
-    if (comparePosition(original, this.last.original)
-        || comparePosition(generated, this.last.generated)) {
+    // 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) {
       return;
     }
 
-    this.last = {
-      source: loc.filename || this.opts.sourceFileName,
-      generated: generated,
-      original: original
-    };
+    this._lastGenLine = position.line;
+    this._lastSourceLine = sourcePos.line;
+    this._lastSourceColumn = sourcePos.column;
 
-    map.addMapping(this.last);
+    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,
+      },
+    });
   }
 }
-
-function comparePosition(a, b) {
-  return a.line === b.line &&  a.column === b.column;
-}