Add support to trace preparsing decisions

src/parsing/parser.cc

 // Copyright 2012 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.
 
 #include "src/parsing/parser.h"
 
 #include <memory>
 
 #include "src/api.h"
 #include "src/ast/ast-expression-rewriter.h"
@@ skipping 2678 matching lines @@
     }
 
     if (!is_lazy_top_level_function && !is_lazy_inner_function) {
       body = ParseEagerFunctionBody(function_name, pos, formals, kind,
                                     function_type, CHECK_OK);
 
       materialized_literal_count = function_state.materialized_literal_count();
       expected_property_count = function_state.expected_property_count();
     }
 
-    if (use_temp_zone || is_lazy_top_level_function) {
+    DCHECK(use_temp_zone || !is_lazy_top_level_function);
+    if (use_temp_zone) {
       // If the preconditions are correct the function body should never be
       // accessed, but do this anyway for better behaviour if they're wrong.
       body = nullptr;
       scope->AnalyzePartially(&previous_zone_ast_node_factory);
     }
 
+    if (FLAG_trace_preparse) {
+      PrintF("  [%s]: %i-%i %.*s\n",
+             is_lazy_top_level_function
+                 ? "Preparse no-resolution"
+                 : (use_temp_zone ? "Preparse resolution" : "Full parse"),
+             scope->start_position(), scope->end_position(),
+             function_name->byte_length(), function_name->raw_data());
+    }
+
     // Parsing the body may change the language mode in our scope.
     language_mode = scope->language_mode();
 
     // Validate name and parameter names. We can do this only after parsing the
     // function, since the function can declare itself strict.
     CheckFunctionName(language_mode, function_name, function_name_validity,
                       function_name_location, CHECK_OK);
     const bool allow_duplicate_parameters =
         is_sloppy(language_mode) && formals.is_simple && !IsConciseMethod(kind);
     ValidateFormalParameters(language_mode, allow_duplicate_parameters,
@@ skipping 2682 matching lines @@
 
   return final_loop;
 }
 
 #undef CHECK_OK
 #undef CHECK_OK_VOID
 #undef CHECK_FAILED
 
 }  // namespace internal
 }  // namespace v8