Bug 1432885 - Step in to the first valid step target, r=loganfsmyth.

--HG--
extra : rebase_source : 63a7f8f5f1bc4f416e9a330576dc25ccd57222fc
extra : histedit_source : 71d4d3c9374a1a85c343a7126a10a869cebca11d

devtools/client/debugger/test/mochitest/browser.ini

@@ -666,6 +666,7 @@ support-files =
   examples/doc-event-handler.html
   examples/doc-eval-throw.html
   examples/doc-sourceURL-breakpoint.html
+  examples/doc-step-in-uninitialized.html
 
 [browser_dbg-asm.js]
 [browser_dbg-audiocontext.js]
@@ -779,6 +780,7 @@ skip-if = os == 'linux' && !asan # bug 1447118
 skip-if = true
 [browser_dbg-stepping.js]
 skip-if = debug || (verify && (os == 'win')) || (os == "win" && os_version == "6.1")
+[browser_dbg-step-in-uninitialized.js]
 [browser_dbg-tabs.js]
 [browser_dbg-tabs-keyboard.js]
 skip-if = os == "win"

devtools/client/debugger/test/mochitest/browser_dbg-step-in-uninitialized.js

@@ -0,0 +1,38 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+// When stepping into a function, 'let' variables should show as uninitialized
+// instead of undefined.
+
+function findNodeValue(dbg, text) {
+  for (let index = 0;; index++) {
+    var elem = findElement(dbg, "scopeNode", index);
+    if (elem && elem.innerText == text) {
+      return findElement(dbg, "scopeValue", index).innerText;
+    }
+  }
+}
+
+add_task(async function test() {
+  const dbg = await initDebugger("doc-step-in-uninitialized.html");
+  invokeInTab("main");
+  await waitForPaused(dbg, "doc-step-in-uninitialized.html");
+
+  await stepOver(dbg);
+  await stepIn(dbg);
+
+  assertDebugLine(dbg, 8);
+  assertPausedLocation(dbg);
+
+  // We step past the 'let x' at the start of the function because it is not
+  // a breakpoint position.
+  ok(findNodeValue(dbg, "x") == "undefined", "x undefined");
+  ok(findNodeValue(dbg, "y") == "(uninitialized)", "y uninitialized");
+
+  await stepOver(dbg);
+
+  assertDebugLine(dbg, 9);
+
+  ok(findNodeValue(dbg, "y") == "3", "y initialized");
+});

devtools/client/debugger/test/mochitest/examples/doc-step-in-uninitialized.html

@@ -0,0 +1,11 @@
+<script>
+function main() {
+  debugger;
+  foo();
+}
+function foo() {
+  let x;
+  let y = 3;
+  return 0;
+}
+</script>

devtools/server/actors/thread.js

@@ -557,7 +557,7 @@ const ThreadActor = ActorClassWithSpec(threadSpec, {
     return this._parentClosed ? null : undefined;
   },
 
-  _makeOnEnterFrame: function({ pauseAndRespond }) {
+  _makeOnEnterFrame: function({ thread, pauseAndRespond }) {
     return frame => {
       const { generatedSourceActor } = this.sources.getFrameLocation(frame);
 
@@ -566,7 +566,27 @@ const ThreadActor = ActorClassWithSpec(threadSpec, {
         return undefined;
       }
 
-      return pauseAndRespond(frame);
+      // If the initial frame offset is a step target, we are done.
+      if (frame.script.getOffsetMetadata(frame.offset).isStepStart) {
+        return pauseAndRespond(frame);
+      }
+
+      // Continue forward until we get to a valid step target.
+      const { onStep, onPop } = thread._makeSteppingHooks(
+        null, "next", false, null
+      );
+
+      if (thread.dbg.replaying) {
+        const offsets =
+          thread._findReplayingStepOffsets(null, frame,
+                                           /* rewinding = */ false);
+        frame.setReplayingOnStep(onStep, offsets);
+      } else {
+        frame.onStep = onStep;
+      }
+
+      frame.onPop = onPop;
+      return undefined;
     };
   },
 
@@ -646,7 +666,7 @@ const ThreadActor = ActorClassWithSpec(threadSpec, {
 
     const generatedLocation = this.sources.getScriptOffsetLocation(script, offset);
 
-    if (startLocation.generatedUrl !== generatedLocation.generatedUrl) {
+    if (!startLocation || startLocation.generatedUrl !== generatedLocation.generatedUrl) {
       return true;
     }
 
@@ -675,12 +695,6 @@ const ThreadActor = ActorClassWithSpec(threadSpec, {
 
   _makeOnStep: function({ thread, pauseAndRespond, startFrame,
                           startLocation, steppingType, completion, rewinding }) {
-    // Breaking in place: we should always pause.
-    if (steppingType === "break") {
-      return () => pauseAndRespond(this);
-    }
-
-    // Otherwise take what a "step" means into consideration.
     return function() {
       // onStep is called with 'this' set to the current frame.