module: port source map sorting logic from chromium

bcoe · bcoe · commit 584bdd8af85c · 2020-02-23T19:19:18.000-08:00
Digging in to the delta between V8's source map library, and chromium's the most significant difference that jumped out at me was that we were failing to sort generated columns. Since negative offsets are not restricted in the spec, this can lead to bugs. fixes: #31286
diff --git a/lib/internal/source_map/source_map.js b/lib/internal/source_map/source_map.js
@@ -212,6 +212,7 @@ class SourceMap {
     let sourceIndex = 0;
     let sourceLineNumber = 0;
     let sourceColumnNumber = 0;
+    let hadNegativeColumnOffset = false;
 
     const sources = [];
     const originalToCanonicalURLMap = {};
@@ -241,7 +242,13 @@ class SourceMap {
           break;
       }
 
-      columnNumber += decodeVLQ(stringCharIterator);
+      // A negative columnOffset is valid, and if one is observed sorting is
+      // necessary, see: https://github.com/mozilla/source-map/pull/92
+      const columnOffset = decodeVLQ(stringCharIterator);
+      if (columnOffset < 0) {
+        hadNegativeColumnOffset = true;
+      }
+      columnNumber += columnOffset;
       if (isSeparator(stringCharIterator.peek())) {
         this.#mappings.push([lineNumber, columnNumber]);
         continue;
@@ -261,6 +268,9 @@ class SourceMap {
       this.#mappings.push([lineNumber, columnNumber, sourceURL,
                            sourceLineNumber, sourceColumnNumber]);
     }
+    if (hadNegativeColumnOffset) {
+      this.#mappings.sort(compareSourceMapEntry);
+    }
   };
 }
 
@@ -321,6 +331,21 @@ function cloneSourceMapV3(payload) {
   return payload;
 }
 
+/**
+ * @param {Array} entry1 source map entry [lineNumber, columnNumber, sourceURL,
+ *  sourceLineNumber, sourceColumnNumber]
+ * @param {Array} entry2 source map entry.
+ * @return {number}
+ */
+function compareSourceMapEntry(entry1, entry2) {
+  const [lineNumber1, columnNumber1] = entry1;
+  const [lineNumber2, columnNumber2] = entry2;
+  if (lineNumber1 !== lineNumber2) {
+    return lineNumber1 - lineNumber2;
+  }
+  return columnNumber1 - columnNumber2;
+}
+
 module.exports = {
   SourceMap
 };
diff --git a/test/parallel/test-source-map-api.js b/test/parallel/test-source-map-api.js
@@ -124,3 +124,28 @@ const { readFileSync } = require('fs');
     assert.strictEqual(originalColumn, knownDecodings[column]);
   }
 }
+
+// Test that generated columns are sorted when a negative offset is
+// observed, see: https://github.com/mozilla/source-map/pull/92
+{
+  function makeMinimalMap(generatedColumns, originalColumns) {
+    return {
+      sources: ['test.js'],
+      // Mapping from the 0th line, 0th column of the output file to the 0th
+      // source file, 0th line, ${column}th column.
+      mappings: generatedColumns.map((g, i) => `${g}AA${originalColumns[i]}`)
+        .join(',')
+    };
+  }
+  // U = 10
+  // F = -2
+  // A = 0
+  // E = 2
+  const sourceMap = new SourceMap(makeMinimalMap(
+    ['U', 'F', 'F'],
+    ['A', 'E', 'E']
+  ));
+  assert.strictEqual(sourceMap.findEntry(0, 6).originalColumn, 4);
+  assert.strictEqual(sourceMap.findEntry(0, 8).originalColumn, 2);
+  assert.strictEqual(sourceMap.findEntry(0, 10).originalColumn, 0);
+}
