[sdk] Decode 'isScope' flag for generated ranges

The flag was added a while ago to the "Scopes" proposal with the
PR https://github.com/tc39/source-map/pull/69.

We need in DevTools to figure out inlined function scopes.

R=kimanh@chromium.org

Bug: 40277685
Change-Id: I5d25fa2d235256f965bef9d54944876018e44b90
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/5639705
Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Kim-Anh Tran <kimanh@chromium.org>

front_end/core/sdk/SourceMapScopes.test.ts

@@ -386,4 +386,20 @@ describe('decodeGeneratedRanges', () => {
       {from: {line: 0, column: 60}, to: {line: 0, column: 100}, value: 'y'},
     ]);
   });
+
+  it('decodes the "isScope" flag', () => {
+    const range = new GeneratedRangeBuilder()
+                      .start(0, 0)
+                      .start(5, 0, {isScope: true})
+                      .end(10, 0)
+                      .start(20, 4, {isScope: false})
+                      .end(30, 0)
+                      .end(40, 0)
+                      .build();
+
+    const generatedRange = decodeGeneratedRanges(range, [], []);
+    assert.lengthOf(generatedRange.children, 2);
+    assert.isTrue(generatedRange.children[0].isScope);
+    assert.isFalse(generatedRange.children[1].isScope);
+  });
 });

front_end/core/sdk/SourceMapScopes.ts

@@ -34,6 +34,11 @@ export interface GeneratedRange {
   end: Position;
   originalScope?: OriginalScope;
 
+  /**
+   * Whether this generated range is an actual JavaScript scope in the generated code.
+   */
+  isScope: boolean;
+
   /**
    * If this `GeneratedRange` is the result of inlining `originalScope`, then `callsite`
    * refers to where `originalScope` was called in the original ("authored") code.
@@ -188,6 +193,7 @@ export function decodeGeneratedRanges(
       const range: GeneratedRange = {
         start: {line: item.line, column: item.column},
         end: {line: item.line, column: item.column},
+        isScope: Boolean(item.flags & EncodedGeneratedRangeFlag.IsScope),
         values: [],
         children: [],
       };
@@ -289,6 +295,7 @@ interface EncodedGeneratedRangeEnd {
 export const enum EncodedGeneratedRangeFlag {
   HasDefinition = 0x1,
   HasCallsite = 0x2,
+  IsScope = 0x4,
 }
 
 function isRangeStart(item: EncodedGeneratedRangeStart|EncodedGeneratedRangeEnd): item is EncodedGeneratedRangeStart {

front_end/testing/SourceMapEncoder.ts

@@ -200,6 +200,7 @@ export class GeneratedRangeBuilder {
   };
 
   start(line: number, column: number, options?: {
+    isScope?: boolean,
     definition?: {sourceIdx: number, scopeIdx: number},
     callsite?: {sourceIdx: number, line: number, column: number},
     bindings?: (number|{line: number, column: number, nameIdx: number}[])[],
@@ -220,6 +221,9 @@ export class GeneratedRangeBuilder {
     if (options?.callsite) {
       flags |= SDK.SourceMapScopes.EncodedGeneratedRangeFlag.HasCallsite;
     }
+    if (options?.isScope) {
+      flags |= SDK.SourceMapScopes.EncodedGeneratedRangeFlag.IsScope;
+    }
     this.#encodedRange += encodeVlq(flags);
 
     if (options?.definition) {