1 files changed, 193 insertions, 0 deletions
diff --git a/packages/bun-debug-adapter-protocol/src/debugger/sourcemap.ts b/packages/bun-debug-adapter-protocol/src/debugger/sourcemap.ts
new file mode 100644
index 000000000..3b3f05c6b
--- /dev/null
+++ b/packages/bun-debug-adapter-protocol/src/debugger/sourcemap.ts
@@ -0,0 +1,193 @@
+import type { LineRange, MappedPosition } from "source-map-js";
+import { SourceMapConsumer } from "source-map-js";
+
+export type LocationRequest = {
+  line?: number;
+  column?: number;
+  url?: string;
+};
+
+export type Location = {
+  line: number; // 0-based
+  column: number; // 0-based
+} & (
+  | {
+      verified: true;
+    }
+  | {
+      verified?: false;
+      message?: string;
+    }
+);
+
+export interface SourceMap {
+  generatedLocation(request: LocationRequest): Location;
+  originalLocation(request: LocationRequest): Location;
+}
+
+class ActualSourceMap implements SourceMap {
+  #sourceMap: SourceMapConsumer;
+  #sources: string[];
+
+  constructor(sourceMap: SourceMapConsumer) {
+    this.#sourceMap = sourceMap;
+    this.#sources = (sourceMap as any)._absoluteSources;
+  }
+
+  #getSource(url?: string): string {
+    const sources = this.#sources;
+    if (!sources.length) {
+      return "";
+    }
+    if (sources.length === 1 || !url) {
+      return sources[0];
+    }
+    for (const source of sources) {
+      if (url.endsWith(source)) {
+        return source;
+      }
+    }
+    return "";
+  }
+
+  generatedLocation(request: LocationRequest): Location {
+    const { line, column, url } = request;
+
+    let lineRange: LineRange;
+    try {
+      const source = this.#getSource(url);
+      lineRange = this.#sourceMap.generatedPositionFor({
+        line: lineTo1BasedLine(line),
+        column: columnToColumn(column),
+        source,
+      });
+    } catch (error) {
+      return {
+        line: lineToLine(line),
+        column: columnToColumn(column),
+        verified: false,
+        message: unknownToError(error),
+      };
+    }
+
+    if (!locationIsValid(lineRange)) {
+      return {
+        line: lineToLine(line),
+        column: columnToColumn(column),
+        verified: false,
+      };
+    }
+
+    const { line: gline, column: gcolumn } = lineRange;
+    return {
+      line: lineToLine(gline),
+      column: columnToColumn(gcolumn),
+      verified: true,
+    };
+  }
+
+  originalLocation(request: LocationRequest): Location {
+    const { line, column } = request;
+
+    let mappedPosition: MappedPosition;
+    try {
+      mappedPosition = this.#sourceMap.originalPositionFor({
+        line: lineTo1BasedLine(line),
+        column: columnToColumn(column),
+      });
+    } catch (error) {
+      return {
+        line: lineToLine(line),
+        column: columnToColumn(column),
+        verified: false,
+        message: unknownToError(error),
+      };
+    }
+
+    if (!locationIsValid(mappedPosition)) {
+      return {
+        line: lineToLine(line),
+        column: columnToColumn(column),
+        verified: false,
+      };
+    }
+
+    const { line: oline, column: ocolumn } = mappedPosition;
+    return {
+      line: lineTo0BasedLine(oline),
+      column: columnToColumn(ocolumn),
+      verified: true,
+    };
+  }
+}
+
+class NoopSourceMap implements SourceMap {
+  generatedLocation(request: LocationRequest): Location {
+    const { line, column } = request;
+    return {
+      line: lineToLine(line),
+      column: columnToColumn(column),
+      verified: true,
+    };
+  }
+
+  originalLocation(request: LocationRequest): Location {
+    const { line, column } = request;
+    return {
+      line: lineToLine(line),
+      column: columnToColumn(column),
+      verified: true,
+    };
+  }
+}
+
+const defaultSourceMap = new NoopSourceMap();
+
+export function SourceMap(url?: string): SourceMap {
+  if (!url || !url.startsWith("data:")) {
+    return defaultSourceMap;
+  }
+  try {
+    const [_, base64] = url.split(",", 2);
+    const decoded = Buffer.from(base64, "base64url").toString("utf8");
+    const schema = JSON.parse(decoded);
+    const sourceMap = new SourceMapConsumer(schema);
+    return new ActualSourceMap(sourceMap);
+  } catch (error) {
+    console.warn("Failed to parse source map URL", url);
+  }
+  return defaultSourceMap;
+}
+
+function lineTo1BasedLine(line?: number): number {
+  return numberIsValid(line) ? line + 1 : 1;
+}
+
+function lineTo0BasedLine(line?: number): number {
+  return numberIsValid(line) ? line - 1 : 0;
+}
+
+function lineToLine(line?: number): number {
+  return numberIsValid(line) ? line : 0;
+}
+
+function columnToColumn(column?: number): number {
+  return numberIsValid(column) ? column : 0;
+}
+
+function locationIsValid(location: Location): location is Location {
+  const { line, column } = location;
+  return numberIsValid(line) && numberIsValid(column);
+}
+
+function numberIsValid(number?: number): number is number {
+  return typeof number === "number" && isFinite(number) && number >= 0;
+}
+
+function unknownToError(error: unknown): string {
+  if (error instanceof Error) {
+    const { message } = error;
+    return message;
+  }
+  return String(error);
+}