Implement loose/strict decoding for scope start/end

Author: szuend

src/decode/decode.test.ts

@@ -12,7 +12,7 @@ import {
   assertThrows,
 } from "jsr:@std/assert";
 import { encodeSigned, encodeUnsigned } from "../vlq.ts";
-import { decode } from "./decode.ts";
+import { decode, DecodeMode } from "./decode.ts";
 import type { SourceMapJson } from "../scopes.d.ts";
 import { OriginalScopeFlags, Tag } from "../codec.ts";
 
@@ -142,11 +142,39 @@ describe("decode", () => {
     assertStrictEquals(info.scopes[0].kind, undefined);
   });
 
-  it("throws when encountering an ORIGINAL_SCOPE_END without start", () => {
+  it("throws when encountering an ORIGINAL_SCOPE_END without start in strict mode", () => {
     const encoder = new ItemEncoder();
     encoder.addUnsignedVLQs(Tag.ORIGINAL_SCOPE_END, 0, 0).finishItem();
     const map = createMap(encoder.encode(), []);
 
-    assertThrows(() => decode(map));
+    assertThrows(() => decode(map, { mode: DecodeMode.STRICT }));
+  });
+
+  it("ignores miss-matched ORIGINAL_SCOPE_END items", () => {
+    const encoder = new ItemEncoder();
+    encoder.addUnsignedVLQs(Tag.ORIGINAL_SCOPE_END, 0, 0).finishItem();
+    const map = createMap(encoder.encode(), []);
+
+    const info = decode(map, { mode: DecodeMode.LOOSE });
+
+    assertEquals(info.scopes, []);
+  });
+
+  it("throws in strict mode when there are 'open' scopes left at the end", () => {
+    const encoder = new ItemEncoder();
+    encoder.addUnsignedVLQs(Tag.ORIGINAL_SCOPE_START, 0, 0, 0).finishItem();
+    const map = createMap(encoder.encode(), []);
+
+    assertThrows(() => decode(map, { mode: DecodeMode.STRICT }));
+  });
+
+  it("ignores 'open' scopes left at the end in loose mode", () => {
+    const encoder = new ItemEncoder();
+    encoder.addUnsignedVLQs(Tag.ORIGINAL_SCOPE_START, 0, 0, 0).finishItem();
+    const map = createMap(encoder.encode(), []);
+
+    const info = decode(map, { mode: DecodeMode.LOOSE });
+
+    assertEquals(info.scopes, []);
   });
 });

src/decode/decode.ts

@@ -139,9 +139,10 @@ class Decoder {
 
           const scope = this.#scopeStack.pop();
           if (!scope) {
-            throw new Error(
+            this.#throwInStrictMode(
               "Encountered ORIGINAL_SCOPE_END without matching ORIGINAL_SCOPE_START!",
             );
+            continue;
           }
 
           scope.end = { line: this.#scopeState.line, column: item.column };
@@ -244,6 +245,12 @@ class Decoder {
       }
     }
 
+    if (this.#scopeStack.length > 0) {
+      this.#throwInStrictMode(
+        "Encountered ORIGINAL_SCOPE_START without matching END!",
+      );
+    }
+
     const info = { scopes: this.#scopes, ranges: this.#ranges };
 
     this.#scopes = [];
@@ -356,4 +363,8 @@ class Decoder {
       yield EmptyItem;
     }
   }
+
+  #throwInStrictMode(message: string) {
+    if (this.#mode === DecodeMode.STRICT) throw new Error(message);
+  }
 }