Implement rudimentary CallSite encoding/decoding

Author: szuend

src/codec.ts

@@ -9,6 +9,7 @@ export const enum Tag {
   GENERATED_RANGE_START = 0x5,
   GENERATED_RANGE_END = 0x6,
   GENERATED_RANGE_BINDINGS = 0x7,
+  GENERATED_RANGE_CALL_SITE = 0x9,
 }
 
 export const enum EncodedTag {
@@ -18,6 +19,7 @@ export const enum EncodedTag {
   GENERATED_RANGE_START = "F", // 0x5
   GENERATED_RANGE_END = "G", // 0x6
   GENERATED_RANGE_BINDINGS = "H", // 0x7
+  GENERATED_RANGE_CALL_SITE = "J", // 0x9
 }
 
 export const enum OriginalScopeFlags {

src/decode/decode.ts

@@ -171,6 +171,14 @@ class Decoder {
           this.#handleGeneratedRangeBindingsItem(valueIdxs);
           break;
         }
+        case Tag.GENERATED_RANGE_CALL_SITE: {
+          this.#handleGeneratedRangeCallSite(
+            iter.nextSignedVLQ(),
+            iter.nextSignedVLQ(),
+            iter.nextSignedVLQ(),
+          );
+          break;
+        }
       }
 
       // Consume any trailing VLQ and the the ","
@@ -331,6 +339,35 @@ class Decoder {
     }
   }
 
+  #handleGeneratedRangeCallSite(
+    sourceIndex: number,
+    line: number,
+    column: number,
+  ) {
+    const range = this.#rangeStack.at(-1);
+    if (!range) {
+      // TODO: Throw in strict mode.
+      return;
+    }
+
+    if (sourceIndex === 0 && line === 0) {
+      this.#rangeState.callsiteColumn += column;
+    } else if (sourceIndex === 0) {
+      this.#rangeState.callsiteLine += line;
+      this.#rangeState.callsiteColumn = column;
+    } else {
+      this.#rangeState.callsiteSourceIdx += sourceIndex;
+      this.#rangeState.callsiteLine = line;
+      this.#rangeState.callsiteColumn = column;
+    }
+
+    range.callSite = {
+      sourceIndex: this.#rangeState.callsiteSourceIdx,
+      line: this.#rangeState.callsiteLine,
+      column: this.#rangeState.callsiteColumn,
+    };
+  }
+
   #handleGeneratedRangeEndItem(line: number, column: number) {
     if (line !== 0) {
       this.#rangeState.line += line;

src/encode/encoder.ts

@@ -144,6 +144,7 @@ export class Encoder {
   #encodeGeneratedRange(range: GeneratedRange): void {
     this.#encodeGeneratedRangeStart(range);
     this.#encodeGeneratedRangeBindings(range);
+    this.#encodeGeneratedRangeCallSite(range);
     range.children.forEach((child) => this.#encodeGeneratedRange(child));
     this.#encodeGeneratedRangeEnd(range);
   }
@@ -210,6 +211,29 @@ export class Encoder {
     this.#finishItem();
   }
 
+  #encodeGeneratedRangeCallSite(range: GeneratedRange) {
+    if (!range.callSite) return;
+    const { sourceIndex, line, column } = range.callSite;
+
+    // TODO: Throw if stackFrame flag is set or OriginalScope index is invalid or no generated range is here.
+
+    const encodedSourceIndex = sourceIndex - this.#rangeState.callsiteSourceIdx;
+    const encodedLine = encodedSourceIndex == 0
+      ? line - this.#rangeState.callsiteLine
+      : line;
+    const encodedColumn = encodedLine == 0
+      ? column - this.#rangeState.callsiteColumn
+      : column;
+
+    this.#rangeState.callsiteSourceIdx = sourceIndex;
+    this.#rangeState.callsiteLine = line;
+    this.#rangeState.callsiteColumn = column;
+
+    this.#encodeTag(EncodedTag.GENERATED_RANGE_CALL_SITE).#encodeSigned(
+      encodedSourceIndex,
+    ).#encodeSigned(encodedLine).#encodeSigned(encodedColumn).#finishItem();
+  }
+
   #encodeGeneratedRangeEnd(range: GeneratedRange) {
     const { line, column } = range.end;
     this.#verifyPositionWithRangeState(line, column);

src/roundtrip.test.ts

@@ -157,4 +157,29 @@ describe("round trip", () => {
 
     assertCodec(builder.build());
   });
+
+  it("handles callSites for inlined ranges", () => {
+    builder.startScope(0, 0, { key: "global" }).startScope(10, 0, {
+      key: "function",
+    }).endScope(20, 0).endScope(30, 0)
+      .startRange(0, 0, { scopeKey: "global" })
+      .startRange(0, 10, {
+        scopeKey: "function",
+        callSite: { sourceIndex: 0, line: 30, column: 5 },
+      })
+      .endRange(0, 20)
+      .startRange(0, 30, {
+        scopeKey: "function",
+        callSite: { sourceIndex: 0, line: 30, column: 20 },
+      })
+      .endRange(0, 40)
+      .startRange(0, 50, {
+        scopeKey: "function",
+        callSite: { sourceIndex: 0, line: 40, column: 2 },
+      })
+      .endRange(0, 60)
+      .endRange(0, 70);
+
+    assertCodec(builder.build());
+  });
 });