[parser] Force func decl allocation for code coverage

Preserve coverage for unused functions by force marking them used when
code coverage is enabled.

Bug: chromium:927464
Change-Id: Ia973467d06f7268f4e98cc76d0bb98cc591e979c
Reviewed-on: https://chromium-review.googlesource.com/c/1454717
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59373}

src/parsing/parser.cc

@@ -1444,6 +1444,11 @@ Statement* Parser::DeclareFunction(const AstRawString* variable_name,
   bool was_added;
   Declare(declaration, variable_name, kind, mode, kCreatedInitialized, scope(),
           &was_added, beg_pos);
+  if (source_range_map_ != nullptr) {
+    // Force the function to be allocated when collecting source coverage, so
+    // that even dead functions get source coverage data.
+    declaration->var()->set_is_used();
+  }
   if (names) names->Add(variable_name, zone());
   if (kind == SLOPPY_BLOCK_FUNCTION_VARIABLE) {
     Token::Value init = loop_nesting_depth() > 0 ? Token::ASSIGN : Token::INIT;

test/inspector/cpu-profiler/coverage-block-expected.txt

@@ -970,6 +970,17 @@ Running test: testPreciseCountCoveragePartial
                             }
                         ]
                     }
+                    [6] : {
+                        functionName : nested_4
+                        isBlockCoverage : false
+                        ranges : [
+                            [0] : {
+                                count : 0
+                                endOffset : 201
+                                startOffset : 179
+                            }
+                        ]
+                    }
                 ]
                 scriptId : <scriptId>
                 url : testPreciseCountCoveragePartial

test/mjsunit/code-coverage-block.js

@@ -1004,4 +1004,17 @@ c(true); d(true);                         // 1650
  {"start":1403,"end":1503,"count":0}]
 );
 
+TestCoverage(
+"https://crbug.com/927464",
+`
+!function f() {                           // 0000
+  function unused() { nop(); }            // 0100
+  nop();                                  // 0150
+}();                                      // 0200
+`,
+[{"start":0,"end":199,"count":1},
+ {"start":1,"end":151,"count":1},
+ {"start":52,"end":80,"count":0}]
+);
+
 %DebugToggleBlockCoverage(false);