Add sub-range decoding

Author: szuend

src/decode/decode.test.ts

@@ -428,4 +428,68 @@ describe("decode", () => {
 
     assertEquals(info.ranges, []);
   });
+
+  it("throws for multiple GENERATED_RANGE_SUBRANGE_BINDING items for the same variable in strict mode", () => {
+    const encoder = new ItemEncoder();
+    encoder.addUnsignedVLQs(Tag.GENERATED_RANGE_START, 0, 0).finishItem();
+    // Sub-range binding for variable 0
+    encoder.addUnsignedVLQs(Tag.GENERATED_RANGE_SUBRANGE_BINDING, 0, 1, 1, 0)
+      .finishItem();
+    // Duplicate sub-range binding for variable 0
+    encoder.addUnsignedVLQs(Tag.GENERATED_RANGE_SUBRANGE_BINDING, 0, 1, 2, 0)
+      .finishItem();
+    encoder.addUnsignedVLQs(Tag.GENERATED_RANGE_END, 2, 0).finishItem();
+    const map = createMap(encoder.encode(), ["foo"]);
+
+    assertThrows(
+      () => decode(map, { mode: DecodeMode.STRICT }),
+      Error,
+      "Encountered multiple GENERATED_RANGE_SUBRANGE_BINDING items for the same variable",
+    );
+  });
+
+  it("ignores multiple GENERATED_RANGE_SUBRANGE_BINDING items for the same variable in lax mode", () => {
+    const encoder = new ItemEncoder();
+    // Original scope with 1 variable.
+    encoder.addUnsignedVLQs(Tag.ORIGINAL_SCOPE_START, 0, 0, 0).finishItem();
+    encoder.addUnsignedVLQs(Tag.ORIGINAL_SCOPE_VARIABLES, 0).finishItem();
+    encoder.addUnsignedVLQs(Tag.ORIGINAL_SCOPE_END, 1, 0).finishItem();
+
+    // Generated range from 0,0 to 3,0, referencing the original scope.
+    encoder.addUnsignedVLQs(
+      Tag.GENERATED_RANGE_START,
+      GeneratedRangeFlags.HAS_DEFINITION,
+      0,
+      0,
+    ).addSignedVLQs(0).finishItem();
+    // Initial binding for the variable is "bar" (index 2).
+    encoder.addUnsignedVLQs(Tag.GENERATED_RANGE_BINDINGS, 2).finishItem();
+
+    // 1st sub-range binding for variable 0. from 1,0, value is "var1" (index 1)
+    encoder.addUnsignedVLQs(Tag.GENERATED_RANGE_SUBRANGE_BINDING, 0, 1, 1, 0)
+      .finishItem();
+    // 2nd sub-range binding for variable 0. from 2,0, value is "baz" (index 3)
+    encoder.addUnsignedVLQs(Tag.GENERATED_RANGE_SUBRANGE_BINDING, 0, 3, 1, 0)
+      .finishItem();
+    encoder.addUnsignedVLQs(Tag.GENERATED_RANGE_END, 3, 0).finishItem();
+    const map = createMap(encoder.encode(), ["var1", "bar", "baz"]);
+
+    const info = decode(map, { mode: DecodeMode.LAX });
+
+    assertExists(info.ranges[0]);
+    assertEquals(info.ranges[0].values, [
+      [
+        {
+          value: "bar",
+          from: { line: 0, column: 0 },
+          to: { line: 1, column: 0 },
+        },
+        {
+          value: "var1",
+          from: { line: 1, column: 0 },
+          to: { line: 3, column: 0 },
+        },
+      ],
+    ]);
+  });
 });

src/decode/decode.ts

@@ -14,6 +14,7 @@ import type {
   OriginalScope,
   ScopeInfo,
   SourceMapJson,
+  SubRangeBinding,
 } from "../scopes.d.ts";
 import { TokenIterator } from "../vlq.ts";
 
@@ -74,6 +75,7 @@ class Decoder {
   readonly #rangeStack: GeneratedRange[] = [];
 
   #flatOriginalScopes: OriginalScope[] = [];
+  #subRangeBindingsForRange = new Map<number, [number, number, number][]>();
 
   constructor(scopes: string, names: string[], options?: { mode: DecodeMode }) {
     this.#encodedScopes = scopes;
@@ -169,6 +171,21 @@ class Decoder {
           this.#handleGeneratedRangeBindingsItem(valueIdxs);
           break;
         }
+        case Tag.GENERATED_RANGE_SUBRANGE_BINDING: {
+          const variableIndex = iter.nextUnsignedVLQ();
+          const bindings: [number, number, number][] = [];
+
+          while (iter.hasNext() && iter.peek() !== ",") {
+            bindings.push([
+              iter.nextUnsignedVLQ(),
+              iter.nextUnsignedVLQ(),
+              iter.nextUnsignedVLQ(),
+            ]);
+          }
+
+          this.#recordGeneratedSubRangeBindingItem(variableIndex, bindings);
+          break;
+        }
         case Tag.GENERATED_RANGE_CALL_SITE: {
           this.#handleGeneratedRangeCallSite(
             iter.nextUnsignedVLQ(),
@@ -331,6 +348,7 @@ class Decoder {
     }
 
     this.#rangeStack.push(range);
+    this.#subRangeBindingsForRange.clear();
   }
 
   #handleGeneratedRangeBindingsItem(valueIdxs: number[]) {
@@ -351,6 +369,19 @@ class Decoder {
     }
   }
 
+  #recordGeneratedSubRangeBindingItem(
+    variableIndex: number,
+    bindings: [number, number, number][],
+  ) {
+    if (this.#subRangeBindingsForRange.has(variableIndex)) {
+      this.#throwInStrictMode(
+        "Encountered multiple GENERATED_RANGE_SUBRANGE_BINDING items for the same variable",
+      );
+      return;
+    }
+    this.#subRangeBindingsForRange.set(variableIndex, bindings);
+  }
+
   #handleGeneratedRangeCallSite(
     sourceIndex: number,
     line: number,
@@ -392,6 +423,8 @@ class Decoder {
       column: this.#rangeState.column,
     };
 
+    this.#handleGeneratedRangeSubRangeBindings(range);
+
     if (this.#rangeStack.length > 0) {
       const parent = this.#rangeStack.at(-1)!;
       range.parent = parent;
@@ -401,6 +434,48 @@ class Decoder {
     }
   }
 
+  #handleGeneratedRangeSubRangeBindings(range: GeneratedRange) {
+    for (const [variableIndex, bindings] of this.#subRangeBindingsForRange) {
+      const value = range.values[variableIndex];
+      const subRanges: SubRangeBinding[] = [];
+      range.values[variableIndex] = subRanges;
+
+      let lastLine = range.start.line;
+      let lastColumn = range.start.column;
+
+      subRanges.push({
+        from: { line: lastLine, column: lastColumn },
+        to: { line: 0, column: 0 },
+        value: value as string | undefined,
+      });
+
+      for (const [binding, line, column] of bindings) {
+        lastLine += line;
+        if (line === 0) {
+          lastColumn += column;
+        } else {
+          lastColumn = column;
+        }
+
+        subRanges.push({
+          from: { line: lastLine, column: lastColumn },
+          to: { line: 0, column: 0 }, // This will be fixed in the post-processing step.
+          value: binding === 0 ? undefined : this.#resolveName(binding - 1),
+        });
+      }
+    }
+
+    for (const value of range.values) {
+      if (Array.isArray(value)) {
+        const subRanges = value;
+        for (let i = 0; i < subRanges.length - 1; ++i) {
+          subRanges[i].to = subRanges[i + 1].from;
+        }
+        subRanges[subRanges.length - 1].to = range.end;
+      }
+    }
+  }
+
   #resolveName(index: number): string {
     if (index < 0 || index >= this.#names.length) {
       this.#throwInStrictMode("Illegal index into the 'names' array");