6 files changed, 440 insertions, 0 deletions
diff --git a/js/deno.ts b/js/deno.ts
index 32899e045..8dc4fd791 100644
--- a/js/deno.ts
+++ b/js/deno.ts
@@ -58,6 +58,7 @@ export { statSync, lstatSync, stat, lstat } from "./stat";
 export { linkSync, link } from "./link";
 export { symlinkSync, symlink } from "./symlink";
 export { writeFileSync, writeFile, WriteFileOptions } from "./write_file";
+export { applySourceMap } from "./error_stack";
 export { ErrorKind, DenoError } from "./errors";
 export {
   permissions,
@@ -88,6 +89,9 @@ export const args: string[] = [];
 /** @internal */
 export { core } from "./core";
 
+/** @internal */
+export { setPrepareStackTrace } from "./error_stack";
+
 // TODO Don't expose Console nor stringifyArgs.
 /** @internal */
 export { Console, stringifyArgs } from "./console";
diff --git a/js/error_stack.ts b/js/error_stack.ts
new file mode 100644
index 000000000..e97020687
--- /dev/null
+++ b/js/error_stack.ts
@@ -0,0 +1,298 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+// Some of the code here is adapted directly from V8 and licensed under a BSD
+// style license available here: https://github.com/v8/v8/blob/24886f2d1c565287d33d71e4109a53bf0b54b75c/LICENSE.v8
+
+import * as msg from "gen/cli/msg_generated";
+import * as flatbuffers from "./flatbuffers";
+import * as dispatch from "./dispatch";
+import { assert } from "./util";
+
+export interface Location {
+  /** The full url for the module, e.g. `file://some/file.ts` or
+   * `https://some/file.ts`. */
+  filename: string;
+
+  /** The line number in the file.  It is assumed to be 1-indexed. */
+  line: number;
+
+  /** The column number in the file.  It is assumed to be 1-indexed. */
+  column: number;
+}
+
+function req(
+  filename: string,
+  line: number,
+  column: number
+): [flatbuffers.Builder, msg.Any.ApplySourceMap, flatbuffers.Offset] {
+  const builder = flatbuffers.createBuilder();
+  const filename_ = builder.createString(filename);
+  const inner = msg.ApplySourceMap.createApplySourceMap(
+    builder,
+    filename_,
+    // On this side, line/column are 1 based, but in the source maps, they are
+    // 0 based, so we have to convert back and forth
+    line - 1,
+    column - 1
+  );
+  return [builder, msg.Any.ApplySourceMap, inner];
+}
+
+function res(baseRes: msg.Base | null): Location {
+  assert(baseRes != null);
+  assert(baseRes!.innerType() === msg.Any.ApplySourceMap);
+  const res = new msg.ApplySourceMap();
+  assert(baseRes!.inner(res) != null);
+  const filename = res.filename()!;
+  assert(filename != null);
+  return {
+    filename,
+    // On this side, line/column are 1 based, but in the source maps, they are
+    // 0 based, so we have to convert back and forth
+    line: res.line() + 1,
+    column: res.column() + 1
+  };
+}
+
+/** Given a current location in a module, lookup the source location and
+ * return it.
+ *
+ * When Deno transpiles code, it keep source maps of the transpiled code.  This
+ * function can be used to lookup the original location.  This is automatically
+ * done when accessing the `.stack` of an error, or when an uncaught error is
+ * logged.  This function can be used to perform the lookup for creating better
+ * error handling.
+ *
+ * **Note:** `line` and `column` are 1 indexed, which matches display
+ * expectations, but is not typical of most index numbers in Deno.
+ *
+ * An example:
+ *
+ *       const orig = Deno.applySourceMap({
+ *         location: "file://my/module.ts",
+ *         line: 5,
+ *         column: 15
+ *       });
+ *       console.log(`${orig.filename}:${orig.line}:${orig.column}`);
+ *
+ */
+export function applySourceMap(location: Location): Location {
+  const { filename, line, column } = location;
+  return res(dispatch.sendSync(...req(filename, line, column)));
+}
+
+/** Mutate the call site so that it returns the location, instead of its
+ * original location.
+ */
+function patchCallSite(callSite: CallSite, location: Location): CallSite {
+  return {
+    getThis(): unknown {
+      return callSite.getThis();
+    },
+    getTypeName(): string {
+      return callSite.getTypeName();
+    },
+    getFunction(): Function {
+      return callSite.getFunction();
+    },
+    getFunctionName(): string {
+      return callSite.getFunctionName();
+    },
+    getMethodName(): string {
+      return callSite.getMethodName();
+    },
+    getFileName(): string {
+      return location.filename;
+    },
+    getLineNumber(): number {
+      return location.line;
+    },
+    getColumnNumber(): number {
+      return location.column;
+    },
+    getEvalOrigin(): string | null {
+      return callSite.getEvalOrigin();
+    },
+    isToplevel(): boolean {
+      return callSite.isToplevel();
+    },
+    isEval(): boolean {
+      return callSite.isEval();
+    },
+    isNative(): boolean {
+      return callSite.isNative();
+    },
+    isConstructor(): boolean {
+      return callSite.isConstructor();
+    },
+    isAsync(): boolean {
+      return callSite.isAsync();
+    },
+    isPromiseAll(): boolean {
+      return callSite.isPromiseAll();
+    },
+    getPromiseIndex(): number | null {
+      return callSite.getPromiseIndex();
+    }
+  };
+}
+
+/** Return a string representations of a CallSite's method call name
+ *
+ * This is adapted directly from V8.
+ */
+function getMethodCall(callSite: CallSite): string {
+  let result = "";
+
+  const typeName = callSite.getTypeName();
+  const methodName = callSite.getMethodName();
+  const functionName = callSite.getFunctionName();
+
+  if (functionName) {
+    if (typeName) {
+      const startsWithTypeName = functionName.startsWith(typeName);
+      if (!startsWithTypeName) {
+        result += `${typeName}.`;
+      }
+    }
+    result += functionName;
+
+    if (methodName) {
+      if (!functionName.endsWith(methodName)) {
+        result += ` [as ${methodName}]`;
+      }
+    }
+  } else {
+    if (typeName) {
+      result += `${typeName}.`;
+    }
+    if (methodName) {
+      result += methodName;
+    } else {
+      result += "<anonymous>";
+    }
+  }
+
+  return result;
+}
+
+/** Return a string representations of a CallSite's file location
+ *
+ * This is adapted directly from V8.
+ */
+function getFileLocation(callSite: CallSite): string {
+  if (callSite.isNative()) {
+    return "native";
+  }
+
+  let result = "";
+
+  const fileName = callSite.getFileName();
+  if (!fileName && callSite.isEval()) {
+    const evalOrigin = callSite.getEvalOrigin();
+    assert(evalOrigin != null);
+    result += `${evalOrigin}, `;
+  }
+
+  if (fileName) {
+    result += fileName;
+  } else {
+    result += "<anonymous>";
+  }
+
+  const lineNumber = callSite.getLineNumber();
+  if (lineNumber != null) {
+    result += `:${lineNumber}`;
+
+    const columnNumber = callSite.getColumnNumber();
+    if (columnNumber != null) {
+      result += `:${columnNumber}`;
+    }
+  }
+
+  return result;
+}
+
+/** Convert a CallSite to a string.
+ *
+ * This is adapted directly from V8.
+ */
+function callSiteToString(callSite: CallSite): string {
+  let result = "";
+  const functionName = callSite.getFunctionName();
+
+  const isTopLevel = callSite.isToplevel();
+  const isAsync = callSite.isAsync();
+  const isPromiseAll = callSite.isPromiseAll();
+  const isConstructor = callSite.isConstructor();
+  const isMethodCall = !(isTopLevel || isConstructor);
+
+  if (isAsync) {
+    result += "async ";
+  }
+  if (isPromiseAll) {
+    result += `Promise.all (index ${callSite.getPromiseIndex})`;
+    return result;
+  }
+  if (isMethodCall) {
+    result += getMethodCall(callSite);
+  } else if (isConstructor) {
+    result += "new ";
+    if (functionName) {
+      result += functionName;
+    } else {
+      result += "<anonymous>";
+    }
+  } else if (functionName) {
+    result += functionName;
+  } else {
+    result += getFileLocation(callSite);
+    return result;
+  }
+
+  result += ` (${getFileLocation(callSite)})`;
+  return result;
+}
+
+/** A replacement for the default stack trace preparer which will op into Rust
+ * to apply source maps to individual sites
+ */
+function prepareStackTrace(
+  error: Error,
+  structuredStackTrace: CallSite[]
+): string {
+  return (
+    `${error.name}: ${error.message}\n` +
+    structuredStackTrace
+      .map(
+        (callSite): CallSite => {
+          const filename = callSite.getFileName();
+          const line = callSite.getLineNumber();
+          const column = callSite.getColumnNumber();
+          if (filename && line != null && column != null) {
+            return patchCallSite(
+              callSite,
+              applySourceMap({
+                filename,
+                line,
+                column
+              })
+            );
+          }
+          return callSite;
+        }
+      )
+      .map((callSite): string => `    at ${callSiteToString(callSite)}`)
+      .join("\n")
+  );
+}
+
+/** Sets the `prepareStackTrace` method on the Error constructor which will
+ * op into Rust to remap source code for caught errors where the `.stack` is
+ * being accessed.
+ *
+ * See: https://v8.dev/docs/stack-trace-api
+ */
+// @internal
+export function setPrepareStackTrace(ErrorConstructor: typeof Error): void {
+  ErrorConstructor.prepareStackTrace = prepareStackTrace;
+}
diff --git a/js/error_stack_test.ts b/js/error_stack_test.ts
new file mode 100644
index 000000000..0df491f39
--- /dev/null
+++ b/js/error_stack_test.ts
@@ -0,0 +1,111 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+import { test, assert } from "./test_util.ts";
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+const { setPrepareStackTrace } = Deno as any;
+
+interface CallSite {
+  getThis(): unknown;
+  getTypeName(): string;
+  getFunction(): Function;
+  getFunctionName(): string;
+  getMethodName(): string;
+  getFileName(): string;
+  getLineNumber(): number | null;
+  getColumnNumber(): number | null;
+  getEvalOrigin(): string | null;
+  isToplevel(): boolean;
+  isEval(): boolean;
+  isNative(): boolean;
+  isConstructor(): boolean;
+  isAsync(): boolean;
+  isPromiseAll(): boolean;
+  getPromiseIndex(): number | null;
+}
+
+function getMockCallSite(
+  filename: string,
+  line: number | null,
+  column: number | null
+): CallSite {
+  return {
+    getThis(): unknown {
+      return undefined;
+    },
+    getTypeName(): string {
+      return "";
+    },
+    getFunction(): Function {
+      return (): void => {};
+    },
+    getFunctionName(): string {
+      return "";
+    },
+    getMethodName(): string {
+      return "";
+    },
+    getFileName(): string {
+      return filename;
+    },
+    getLineNumber(): number | null {
+      return line;
+    },
+    getColumnNumber(): number | null {
+      return column;
+    },
+    getEvalOrigin(): null {
+      return null;
+    },
+    isToplevel(): false {
+      return false;
+    },
+    isEval(): false {
+      return false;
+    },
+    isNative(): false {
+      return false;
+    },
+    isConstructor(): false {
+      return false;
+    },
+    isAsync(): false {
+      return false;
+    },
+    isPromiseAll(): false {
+      return false;
+    },
+    getPromiseIndex(): null {
+      return null;
+    }
+  };
+}
+
+test(function prepareStackTrace(): void {
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  const MockError = {} as any;
+  setPrepareStackTrace(MockError);
+  assert(typeof MockError.prepareStackTrace === "function");
+  const prepareStackTrace: (
+    error: Error,
+    structuredStackTrace: CallSite[]
+  ) => string = MockError.prepareStackTrace;
+  const result = prepareStackTrace(new Error("foo"), [
+    getMockCallSite("gen/cli/bundle/main.js", 23, 0)
+  ]);
+  assert(result.startsWith("Error: foo\n"));
+  assert(
+    result.includes("<anonymous> (js/"),
+    "should remap to something in 'js/'"
+  );
+});
+
+test(function applySourceMap(): void {
+  const result = Deno.applySourceMap({
+    filename: "gen/cli/bundle/main.js",
+    line: 23,
+    column: 0
+  });
+  assert(result.filename.startsWith("js/"));
+  assert(result.line != null);
+  assert(result.column != null);
+});
diff --git a/js/globals.ts b/js/globals.ts
index cff4b7dd9..27cef3909 100644
--- a/js/globals.ts
+++ b/js/globals.ts
@@ -40,6 +40,29 @@ import { immutableDefine } from "./util";
 declare global {
   const console: consoleTypes.Console;
   const setTimeout: typeof timers.setTimeout;
+
+  interface CallSite {
+    getThis(): unknown;
+    getTypeName(): string;
+    getFunction(): Function;
+    getFunctionName(): string;
+    getMethodName(): string;
+    getFileName(): string;
+    getLineNumber(): number | null;
+    getColumnNumber(): number | null;
+    getEvalOrigin(): string | null;
+    isToplevel(): boolean;
+    isEval(): boolean;
+    isNative(): boolean;
+    isConstructor(): boolean;
+    isAsync(): boolean;
+    isPromiseAll(): boolean;
+    getPromiseIndex(): number | null;
+  }
+
+  interface ErrorConstructor {
+    prepareStackTrace(error: Error, structuredStackTrace: CallSite[]): string;
+  }
 }
 
 // A self reference to the global object.
diff --git a/js/main.ts b/js/main.ts
index cb27690b5..5687a6926 100644
--- a/js/main.ts
+++ b/js/main.ts
@@ -8,6 +8,7 @@ import "./globals";
 import { assert, log } from "./util";
 import * as os from "./os";
 import { args } from "./deno";
+import { setPrepareStackTrace } from "./error_stack";
 import { replLoop } from "./repl";
 import { xevalMain, XevalFunc } from "./xeval";
 import { setVersions } from "./version";
@@ -30,6 +31,8 @@ export default function denoMain(name?: string): void {
     os.exit(0);
   }
 
+  setPrepareStackTrace(Error);
+
   const mainModule = startResMsg.mainModule();
   if (mainModule) {
     assert(mainModule.length > 0);
diff --git a/js/unit_tests.ts b/js/unit_tests.ts
index ff9f459e5..b55c1954a 100644
--- a/js/unit_tests.ts
+++ b/js/unit_tests.ts
@@ -13,6 +13,7 @@ import "./console_test.ts";
 import "./copy_file_test.ts";
 import "./custom_event_test.ts";
 import "./dir_test.ts";
+import "./error_stack_test.ts";
 import "./event_test.ts";
 import "./event_target_test.ts";
 import "./fetch_test.ts";