Start with range start/end encoding/decoding

Author: szuend

src/builder/builder.ts

@@ -84,15 +84,20 @@ export class ScopeInfoBuilder {
   }
 
   startRange(line: number, column: number): this {
-    this.#rangeStack.push({
+    const range: GeneratedRange = {
       start: { line, column },
       end: { line, column },
       isStackFrame: false,
       isHidden: false,
       values: [],
       children: [],
-      parent: this.#rangeStack.at(-1),
-    });
+    };
+
+    if (this.#rangeStack.length > 0) {
+      range.parent = this.#rangeStack.at(-1);
+    }
+
+    this.#rangeStack.push(range);
 
     return this;
   }

src/codec.ts

@@ -33,9 +33,9 @@ export const EmptyItem = Symbol("empty item");
 export type Item =
   | typeof EmptyItem
   | OriginalScopeStartItem
-  | OriginalScopeEndItem;
-// | GeneratedStartItem
-// | GeneratedEndItem
+  | OriginalScopeEndItem
+  | GeneratedRangeStartItem
+  | GeneratedRangeEndItem;
 // | VariablesItem
 // | BindingsItem;
 
@@ -53,3 +53,16 @@ interface OriginalScopeEndItem {
   line: number;
   column: number;
 }
+
+interface GeneratedRangeStartItem {
+  tag: Tag.GENERATED_RANGE_START;
+  flags: number;
+  line?: number;
+  column: number;
+}
+
+interface GeneratedRangeEndItem {
+  tag: Tag.GENERATED_RANGE_END;
+  line?: number;
+  column: number;
+}

src/decode/decode.ts

@@ -4,6 +4,7 @@
 
 import {
   EmptyItem,
+  GeneratedRangeFlags,
   type Item,
   OriginalScopeFlags,
   type OriginalScopeStartItem,
@@ -112,6 +113,62 @@ class Decoder {
           }
           break;
         }
+        case Tag.GENERATED_RANGE_START: {
+          if (item.line !== undefined) {
+            this.#rangeState.line += item.line;
+            this.#rangeState.column = item.column;
+          } else {
+            this.#rangeState.column += item.column;
+          }
+
+          const range: GeneratedRange = {
+            start: {
+              line: this.#rangeState.line,
+              column: this.#rangeState.column,
+            },
+            end: {
+              line: this.#rangeState.line,
+              column: this.#rangeState.column,
+            },
+            isStackFrame: false,
+            isHidden: false,
+            values: [],
+            children: [],
+          };
+
+          this.#rangeStack.push(range);
+          break;
+        }
+        case Tag.GENERATED_RANGE_END: {
+          if (item.line !== undefined) {
+            this.#rangeState.line += item.line;
+            this.#rangeState.column = item.column;
+          } else {
+            this.#rangeState.column += item.column;
+          }
+
+          const range = this.#rangeStack.pop();
+          if (!range) {
+            throw new Error(
+              "Encountered GENERATED_RANGE_END wtihout matching GENERATED_RANGE_START!",
+            );
+          }
+
+          range.end = {
+            line: this.#rangeState.line,
+            column: this.#rangeState.column,
+          };
+
+          if (this.#rangeStack.length > 0) {
+            const parent = this.#rangeStack.at(-1)!;
+            range.parent = parent;
+            parent.children.push(range);
+          } else {
+            this.#ranges.push(range);
+            Object.assign(this.#rangeState, DEFAULT_RANGE_STATE);
+          }
+          break;
+        }
       }
     }
 
@@ -161,6 +218,33 @@ class Decoder {
           };
           break;
         }
+        case Tag.GENERATED_RANGE_START: {
+          const flags = iter.nextUnsignedVLQ();
+          const line = flags & GeneratedRangeFlags.HAS_LINE
+            ? iter.nextUnsignedVLQ()
+            : undefined;
+
+          yield {
+            tag,
+            flags,
+            line,
+            column: iter.nextUnsignedVLQ(),
+          };
+          break;
+        }
+        case Tag.GENERATED_RANGE_END: {
+          const lineOrColumn = iter.nextUnsignedVLQ();
+          const maybeColumn = iter.hasNext() && iter.peek() !== ","
+            ? iter.nextUnsignedVLQ()
+            : undefined;
+
+          if (maybeColumn !== undefined) {
+            yield { tag, line: lineOrColumn, column: maybeColumn };
+          } else {
+            yield { tag, column: lineOrColumn };
+          }
+          break;
+        }
       }
 
       // Consume any trailing VLQ and the the ","

src/roundtrip.test.ts

@@ -77,4 +77,28 @@ describe("round trip", () => {
 
     assertCodec(builder.build());
   });
+
+  it("handles a single top-level GeneratedRange on the same line", () => {
+    builder.startRange(0, 5).endRange(0, 10);
+
+    assertCodec(builder.build());
+  });
+
+  it("handles a single top-level GeneratedRange that spans multiple lines", () => {
+    builder.startRange(0, 5).endRange(10, 2);
+
+    assertCodec(builder.build());
+  });
+
+  it("handles multiple top-level GeneratedRagnes on the same line", () => {
+    builder.startRange(0, 5).endRange(0, 10).startRange(0, 20).endRange(0, 30);
+
+    assertCodec(builder.build());
+  });
+
+  it("handles multiple top-level GeneratedRanges that span multiple lines", () => {
+    builder.startRange(0, 1).endRange(10, 2).startRange(20, 3).endRange(30, 4);
+
+    assertCodec(builder.build());
+  });
 });