feat: Implement new vendor extension items and invalid items

Author: szuend

src/codec.ts

@@ -12,6 +12,7 @@ export const enum Tag {
   GENERATED_RANGE_BINDINGS = 0x6,
   GENERATED_RANGE_SUBRANGE_BINDING = 0x7,
   GENERATED_RANGE_CALL_SITE = 0x8,
+  VENDOR_EXTENSION = 0x63,
 }
 
 export const enum EncodedTag {
@@ -24,6 +25,7 @@ export const enum EncodedTag {
   GENERATED_RANGE_BINDINGS = "G", // 0x6
   GENERATED_RANGE_SUBRANGE_BINDING = "H", // 0x7
   GENERATED_RANGE_CALL_SITE = "I", // 0x8
+  VENDOR_EXTENSION = "/", //  0x63
 }
 
 export const enum OriginalScopeFlags {

src/decode/decode.test.ts

@@ -557,4 +557,38 @@ describe("decode", () => {
     assertEquals(info.ranges[0].start, { line: 0, column: 0 });
     assertEquals(info.ranges[0].end, { line: 0, column: 10 });
   });
+
+  it("ignores vendor extensions", () => {
+    const encoder = new ItemEncoder();
+    encoder.addUnsignedVLQs(Tag.VENDOR_EXTENSION, 0);
+    encoder.finishItem();
+    const map = createMap(encoder.encode(), ["x_ext_item"]);
+
+    assertEquals(decode(map, { mode: DecodeMode.STRICT }), {
+      scopes: [],
+      ranges: [],
+    });
+  });
+
+  it("throws for invalid item tags in strict mode", () => {
+    const encoder = new ItemEncoder();
+    encoder.addUnsignedVLQs(42, 1, 2, 3);
+    encoder.finishItem();
+    const map = createMap(encoder.encode(), []);
+
+    assertThrows(
+      () => decode(map, { mode: DecodeMode.STRICT }),
+      Error,
+      "Encountered illegal item tag 42",
+    );
+  });
+
+  it("ignores invalid item tags in lax mode", () => {
+    const encoder = new ItemEncoder();
+    encoder.addUnsignedVLQs(42, 1, 2, 3);
+    encoder.finishItem();
+    const map = createMap(encoder.encode(), []);
+
+    assertEquals(decode(map), { scopes: [], ranges: [] });
+  });
 });

src/decode/decode.ts

@@ -143,9 +143,10 @@ class Decoder {
     while (iter.hasNext()) {
       const tag = iter.nextUnsignedVLQ();
       switch (tag) {
-        case Tag.EMPTY:
+        case Tag.EMPTY: {
           this.#scopes.push(null);
           break;
+        }
         case Tag.ORIGINAL_SCOPE_START: {
           const item: OriginalScopeStartItem = {
             flags: iter.nextUnsignedVLQ(),
@@ -245,6 +246,14 @@ class Decoder {
           );
           break;
         }
+        case Tag.VENDOR_EXTENSION: {
+          const _extensionNameIdx = iter.nextUnsignedVLQ();
+          break;
+        }
+        default: {
+          this.#throwInStrictMode(`Encountered illegal item tag ${tag}`);
+          break;
+        }
       }
 
       // Consume any trailing VLQ and the the ","