Implement strict/loose verification for generated range start/end

Author: szuend

src/decode/decode.test.ts

@@ -177,4 +177,44 @@ describe("decode", () => {
 
     assertEquals(info.scopes, []);
   });
+
+  it("throws in strict mode when encountering an GENERATED_RANGE_END without START", () => {
+    const encoder = new ItemEncoder();
+    encoder.addUnsignedVLQs(Tag.GENERATED_RANGE_END);
+    encoder.addSignedVLQs(42).finishItem();
+    const map = createMap(encoder.encode(), []);
+
+    assertThrows(() => decode(map, { mode: DecodeMode.STRICT }));
+  });
+
+  it("ignores GENERATED_RANGE_END items without START in loose mode", () => {
+    const encoder = new ItemEncoder();
+    encoder.addUnsignedVLQs(Tag.GENERATED_RANGE_END);
+    encoder.addSignedVLQs(42).finishItem();
+    const map = createMap(encoder.encode(), []);
+
+    const info = decode(map, { mode: DecodeMode.LOOSE });
+
+    assertEquals(info.ranges, []);
+  });
+
+  it("throws for un-matched GENERATED_RANGE_START at the end in loose mode", () => {
+    const encoder = new ItemEncoder();
+    encoder.addUnsignedVLQs(Tag.GENERATED_RANGE_START, 0);
+    encoder.addSignedVLQs(42).finishItem();
+    const map = createMap(encoder.encode(), []);
+
+    assertThrows(() => decode(map, { mode: DecodeMode.STRICT }));
+  });
+
+  it("ignores un-matched GENERATED_RANGE_START at the end in loose mode", () => {
+    const encoder = new ItemEncoder();
+    encoder.addUnsignedVLQs(Tag.GENERATED_RANGE_START, 0);
+    encoder.addSignedVLQs(42).finishItem();
+    const map = createMap(encoder.encode(), []);
+
+    const info = decode(map, { mode: DecodeMode.LOOSE });
+
+    assertEquals(info.ranges, []);
+  });
 });

src/decode/decode.ts

@@ -203,9 +203,10 @@ class Decoder {
 
           const range = this.#rangeStack.pop();
           if (!range) {
-            throw new Error(
+            this.#throwInStrictMode(
               "Encountered GENERATED_RANGE_END without matching GENERATED_RANGE_START!",
             );
+            continue;
           }
 
           range.end = {
@@ -250,6 +251,11 @@ class Decoder {
         "Encountered ORIGINAL_SCOPE_START without matching END!",
       );
     }
+    if (this.#rangeStack.length > 0) {
+      this.#throwInStrictMode(
+        "Encountered GENERATED_RANGE_START without matching END!",
+      );
+    }
 
     const info = { scopes: this.#scopes, ranges: this.#ranges };