module: port source map sorting logic from chromium

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
 };

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);
+}