[coverage] change block range to avoid ambiguity.

By moving the block range end to left of closing bracket,
we can avoid ambiguity where an open-ended singleton range
could be both interpreted as inside the parent range, or
next to it.

R=verwaest@chromium.org

Bug: v8:8237
Change-Id: Ibc9412b31efe900b6d8bff0d8fa8c52ddfbf460a
Reviewed-on: https://chromium-review.googlesource.com/1254127Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56347}

src/debug/debug-coverage.cc

@@ -81,6 +81,11 @@ std::vector<CoverageBlock> GetSortedBlockData(SharedFunctionInfo* shared) {
   std::vector<CoverageBlock> result;
   if (coverage_info->SlotCount() == 0) return result;
 
+  if (FLAG_trace_block_coverage) {
+    PrintF("Collecting coverage data\n");
+    coverage_info->Print(shared->DebugName()->ToCString());
+  }
+
   for (int i = 0; i < coverage_info->SlotCount(); i++) {
     const int start_pos = coverage_info->StartSourcePosition(i);
     const int until_pos = coverage_info->EndSourcePosition(i);

src/objects/debug-objects.cc

@@ -375,7 +375,7 @@ void CoverageInfo::Print(std::unique_ptr<char[]> function_name) {
 
   for (int i = 0; i < SlotCount(); i++) {
     os << "{" << StartSourcePosition(i) << "," << EndSourcePosition(i) << "}"
-       << std::endl;
+       << ": " << BlockCount(i) << std::endl;
   }
 }
 

src/parsing/parser-base.h

@@ -5093,6 +5093,7 @@ typename ParserBase<Impl>::BlockT ParserBase<Impl>::ParseBlock(
   Expect(Token::LBRACE, CHECK_OK_CUSTOM(NullStatement));
   {
     BlockState block_state(zone(), &scope_);
+    // Scope starts before opening brace.
     scope()->set_start_position(scanner()->location().beg_pos);
     typename Types::Target target(this, body);
 
@@ -5104,9 +5105,10 @@ typename ParserBase<Impl>::BlockT ParserBase<Impl>::ParseBlock(
     }
 
     Expect(Token::RBRACE, CHECK_OK_CUSTOM(NullStatement));
-    int end_pos = end_position();
-    scope()->set_end_position(end_pos);
-    impl()->RecordBlockSourceRange(body, end_pos);
+    // Scope ends after closing brace.
+    scope()->set_end_position(scanner()->location().end_pos);
+    // Coverage range uses position before closing brace.
+    impl()->RecordBlockSourceRange(body, scanner()->location().beg_pos);
     body->set_scope(scope()->FinalizeBlockScope());
   }
   return body;

test/mjsunit/code-coverage-block.js

@@ -471,7 +471,7 @@ TestCoverage(
  {"start":472,"end":503,"count":0},
  {"start":626,"end":653,"count":0},
  {"start":768,"end":803,"count":0},
- {"start":867,"end":869,"count":0}]
+ {"start":867,"end":868,"count":0}]
 );
 
 TestCoverage(
@@ -847,7 +847,7 @@ Util.escape("foo.bar");                   // 0400
 [{"start":0,"end":449,"count":1},
  {"start":64,"end":351,"count":1},
  {"start":112,"end":203,"count":0},
- {"start":303,"end":350,"count":0}]
+ {"start":268,"end":350,"count":0}]
 );
 
 %DebugToggleBlockCoverage(false);

test/mjsunit/regress/regress-8237.js

+// Copyright 2018 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.
+
+// Flags: --allow-natives-syntax --no-always-opt
+// Files: test/mjsunit/code-coverage-utils.js
+
+%DebugToggleBlockCoverage(true);
+
+TestCoverage(
+"Repro for the bug",
+`
+function lib (n) {                        // 0000
+  if (n >= 0) {                           // 0050
+    if (n < 0) {                          // 0100
+      return;                             // 0150
+    }                                     // 0200
+  } else if (foo()) {                     // 0250
+  }                                       // 0300
+}                                         // 0350
+function foo () {                         // 0400
+  console.log('foo')                      // 0450
+  return false                            // 0500
+}                                         // 0550
+lib(1)                                    // 0600
+`,
+[{"start":0,"end":649,"count":1},
+{"start":0,"end":351,"count":1},
+{"start":115,"end":205,"count":0},
+{"start":253,"end":303,"count":0},
+{"start":400,"end":551,"count":0}]
+);
+
+TestCoverage(
+"Variant with omitted brackets",
+`
+function lib (n) {                        // 0000
+  if (n >= 0) {                           // 0050
+    if (n < 0)                            // 0100
+      return;                             // 0150
+  }                                       // 0200
+  else if (foo());                        // 0250
+}                                         // 0300
+function foo () {                         // 0350
+  console.log('foo')                      // 0400
+  return false                            // 0450
+}                                         // 0500
+lib(1)                                    // 0550
+`,
+[{"start":0,"end":599,"count":1},
+{"start":0,"end":301,"count":1},
+{"start":156,"end":163,"count":0},
+{"start":203,"end":268,"count":0},
+{"start":350,"end":501,"count":0}]
+);
+
+%DebugToggleBlockCoverage(false);