[debug] Default to last break index.

When looking up the break index for a given source position, default to
the last break index if there is neither a precise match nor a breakable
position after the source position (in which case we still pick the
first candidate).

Fixed: chromium:1222065
Bug: chromium:901819, chromium:782461, chromium:1222060
Change-Id: I10d6a086b2d5fadc9e6dca0c49ed4187eb0359ff
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2972917
Auto-Submit: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Kim-Anh Tran <kimanh@chromium.org>
Reviewed-by: Kim-Anh Tran <kimanh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75284}

src/debug/debug.cc

@@ -220,18 +220,16 @@ BreakIterator::BreakIterator(Handle<DebugInfo> debug_info)
 }
 
 int BreakIterator::BreakIndexFromPosition(int source_position) {
-  int first_break = break_index();
-  bool first = true;
-  while (!Done()) {
-    int next_position = position();
-    if (source_position == next_position) return break_index();
-    if (source_position <= next_position && first) {
-      first_break = break_index();
-      first = false;
+  for (; !Done(); Next()) {
+    if (source_position <= position()) {
+      int first_break = break_index();
+      for (; !Done(); Next()) {
+        if (source_position == position()) return break_index();
+      }
+      return first_break;
     }
-    Next();
   }
-  return first_break;
+  return break_index();
 }
 
 void BreakIterator::Next() {

test/inspector/regress/regress-crbug-1222065-expected.txt

+Regression test for crbug.com/1222065
+
+Running test: test
+- Debugger.setBreakpoint(foo.js:2:9)
+function foo(x) {
+  return x;#
+}
+
+- Debugger.setBreakpoint(foo.js:3)
+function foo(x) {
+  return x;#
+}
+

test/inspector/regress/regress-crbug-1222065.js

+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+const {session, contextGroup, Protocol} =
+    InspectorTest.start('Regression test for crbug.com/1222065');
+
+const source = `
+function foo(x) {
+  return x;
+}
+`;
+
+InspectorTest.runAsyncTestSuite([
+  async function test() {
+    session.setupScriptMap();
+    await Promise.all([
+      Protocol.Runtime.enable(),
+      Protocol.Debugger.enable()
+    ]);
+    contextGroup.addScript(source, 0, 0, 'foo.js');
+    const { params: { scriptId } } = await Protocol.Debugger.onceScriptParsed();
+
+    InspectorTest.log('- Debugger.setBreakpoint(foo.js:2:9)');
+    let {result: {actualLocation, breakpointId}} = await Protocol.Debugger.setBreakpoint({location: {
+      scriptId,
+      lineNumber: 2,
+      columnNumber: 9,
+    }});
+    await session.logSourceLocation(actualLocation);
+    await Protocol.Debugger.removeBreakpoint({breakpointId});
+
+    InspectorTest.log('- Debugger.setBreakpoint(foo.js:3)');
+    ({result: {actualLocation, breakpointId}} = await Protocol.Debugger.setBreakpoint({location: {
+      scriptId,
+      lineNumber: 3,
+    }}));
+    await session.logSourceLocation(actualLocation);
+    await Protocol.Debugger.removeBreakpoint({breakpointId});
+
+    await Promise.all([
+      Protocol.Runtime.disable(),
+      Protocol.Debugger.disable()
+    ]);
+  }
+]);