remapping: get most test cases passing

* add back line information for traceSegmentsInRange because
  it needs to be represented somehow in the return result
  (an alternative would be a start line + array of arrays)
* fixes most range mapping remapping test failures that came up
  due to rebasing these patches

Author: takikawa

packages/remapping/src/source-map-tree.ts

@@ -262,7 +262,7 @@ export function originalPositionFor(
   // If we couldn't find a segment, then this doesn't exist in the sourcemap.
   if (segment == null) return null;
   const maybeRange = isRange(source.map, segment);
-  let startLine = 0; // FIXME this should be the line of the segment
+  let startLine = line;
   if (maybeRange) {
     startLine = maybeRange.line;
   }
@@ -320,27 +320,25 @@ function originalPositionsForRange(
     ];
   }
 
-  // We additional trace the start position of the range to because we may need to
+  // We additionally trace the start position of the range to because we may need to
   // intersect with a range that starts before the given position, or map the start
   // of the range to it if there aren't any exact hits.
   const initialSegment = traceSegment(source.map, line, column);
   const segments = traceSegmentsInRange(source.map, line, column, endLine, endColumn);
 
   // If tracing the start of the range hits a mapping that isn't in the segmenObjects list,
   // add it to the list to process first.
-  if (initialSegment !== null && (segments.length === 0 || initialSegment !== segments[0])) {
-    segments.splice(0, 0, initialSegment);
+  if (initialSegment !== null && (segments.length === 0 || initialSegment !== segments[0][1])) {
+    segments.splice(0, 0, [line, initialSegment]);
   }
 
   const originalPositions = [];
-  for (const segment of segments) {
+  for (const [startLine, segment] of segments) {
     if (segment == null) continue;
 
-    let startLine = 0; // FIXME this should be the line of the segment
     let childEndLine, endSegment;
     const maybeRange = isRange(source.map, segment);
     if (maybeRange) {
-      startLine = maybeRange.line;
       childEndLine = maybeRange.endLine;
       endSegment = maybeRange.endSegment;
     }

packages/trace-mapping/src/trace-mapping.ts

@@ -289,7 +289,7 @@ export function traceSegmentsInRange(
   startColumn: number,
   endLine: number,
   endColumn: number,
-): Readonly<SourceMapSegment>[] {
+): [number, Readonly<SourceMapSegment>][] {
   const lines = decodedMappings(map);
   const segments = startLine < lines.length ? lines[startLine] : [];
   const memo = cast(map)._decodedMemo;
@@ -309,9 +309,11 @@ export function traceSegmentsInRange(
   const range = (start: number, end: number) => {
     return Array.from({ length: end - start + 1 }, (_, i: number) => i + start);
   };
-  const gen = (line: number) => (index: number) => {
-    return lines[line][index];
-  };
+  function gen(line: number) {
+    return (index: number) : [number, Readonly<SourceMapSegment>] => {
+      return [line, lines[line][index]];
+    };
+  }
 
   function previousPosition(line: number, column: number) {
     if (column === 0) {