fix(browser): validate and bound source-map evidence

src/javascript/sourceMaps/DecodedSourceMap.ts

@@ -0,0 +1,82 @@
+import { TraceMap, decodedMappings } from "@jridgewell/trace-mapping";
+import {
+  SourceMapFormatFailure,
+  type SourceMapLeaf,
+} from "./SourceMapFormat.js";
+
+/** Determine whether a leaf-local mapping falls before its enclosing boundary. */
+export const isBeforeSourceMapLeafStop = (
+  leaf: SourceMapLeaf,
+  line: number,
+  column: number,
+): boolean => {
+  if (leaf.stop === null) return true;
+  const generatedLine = leaf.offset.line + line;
+  const generatedColumn = column + (line === 0 ? leaf.offset.column : 0);
+  return (
+    generatedLine < leaf.stop.line ||
+    (generatedLine === leaf.stop.line && generatedColumn < leaf.stop.column)
+  );
+};
+
+/** Resolve one declaration with the same pinned upstream implementation used by full maps. */
+export const resolveSourceMapSource = (
+  source: string | null,
+  sourceRoot: string | null | undefined,
+  mapUrl: string,
+): string => {
+  const map = new TraceMap(
+    {
+      version: 3,
+      names: [],
+      sources: [source ?? ""],
+      ...(sourceRoot == null ? {} : { sourceRoot }),
+      mappings: "",
+    },
+    mapUrl,
+  );
+  const resolved = map.resolvedSources[0];
+  if (resolved === undefined)
+    throw new SourceMapFormatFailure(
+      "format",
+      "Source-map resolver did not return the requested source identity.",
+    );
+  return resolved;
+};
+
+/** Decode leaf mappings and validate producer indices before any consumer publishes them. */
+export const decodeValidatedSourceMapLeaves = (
+  leaves: readonly SourceMapLeaf[],
+  mapUrl: string,
+  check?: () => void,
+): readonly {
+  readonly leaf: SourceMapLeaf;
+  readonly rows: ReturnType<typeof decodedMappings>;
+  readonly resolvedSources: readonly string[];
+}[] =>
+  leaves.map((leaf) => {
+    check?.();
+    const map = new TraceMap(JSON.stringify(leaf.map), mapUrl);
+    const rows = decodedMappings(map);
+    for (const [line, row] of rows.entries()) {
+      if ((line & 255) === 0) check?.();
+      for (const segment of row) {
+        const generatedLine = leaf.offset.line + line;
+        const generatedColumn =
+          segment[0] + (line === 0 ? leaf.offset.column : 0);
+        if (
+          !Number.isSafeInteger(generatedLine) ||
+          !Number.isSafeInteger(generatedColumn) ||
+          ![1, 4, 5].includes(segment.length) ||
+          segment.some((value) => !Number.isSafeInteger(value) || value < 0) ||
+          (segment.length !== 1 && segment[1] >= leaf.map.sources.length) ||
+          (segment.length === 5 && segment[4] >= leaf.map.names.length)
+        )
+          throw new SourceMapFormatFailure(
+            "format",
+            "Decoded local or absolute position, source index or name index is invalid.",
+          );
+      }
+    }
+    return { leaf, rows, resolvedSources: map.resolvedSources };
+  });