Add --no_fwd_decls option

As requested in #354.  Marks all uses as full uses.  Useful for
compliance with Google C++ Style Guide.

iwyu_globals.cc

@@ -92,6 +92,7 @@ static void PrintHelp(const char* extra_msg) {
          "        the maximum line length can still be exceeded with long\n"
          "        file names (default: 80).\n"
          "   --no_comments: do not add 'why' comments.\n"
+         "   --no_fwd_decls: do not use forward declarations.\n"
          "   --verbose=<level>: the higher the level, the more output.\n"
          "\n"
          "In addition to IWYU-specific options you can specify the following\n"
@@ -160,7 +161,8 @@ CommandlineFlags::CommandlineFlags()
       max_line_length(80),
       prefix_header_include_policy(CommandlineFlags::kAdd),
       pch_in_code(false),
-      no_comments(false) {
+      no_comments(false),
+      no_fwd_decls(false) {
 }
 
 int CommandlineFlags::ParseArgv(int argc, char** argv) {
@@ -176,6 +178,7 @@ int CommandlineFlags::ParseArgv(int argc, char** argv) {
     {"pch_in_code", no_argument, nullptr, 'h'},
     {"max_line_length", optional_argument, nullptr, 'l'},
     {"no_comments", optional_argument, nullptr, 'o'},
+    {"no_fwd_decls", optional_argument, nullptr, 'f'},
     {nullptr, 0, nullptr, 0}
   };
   static const char shortopts[] = "d::p:v:c:m:n";
@@ -189,6 +192,7 @@ int CommandlineFlags::ParseArgv(int argc, char** argv) {
       case 'm': mapping_files.push_back(optarg); break;
       case 'n': no_default_mappings = true; break;
       case 'o': no_comments = true; break;
+      case 'f': no_fwd_decls = true; break;
       case 'x':
         if (strcmp(optarg, "add") == 0) {
           prefix_header_include_policy = CommandlineFlags::kAdd;

iwyu_globals.h

@@ -98,8 +98,9 @@ struct CommandlineFlags {
   int max_line_length;
   // Policy regarding files included via -include option.  No short option.
   PrefixHeaderIncludePolicy prefix_header_include_policy;
-  bool pch_in_code;  // Treat the first seen include as a PCH. No short option.
-  bool no_comments;  // Disable 'why' comments. No short option.
+  bool pch_in_code;   // Treat the first seen include as a PCH. No short option.
+  bool no_comments;   // Disable 'why' comments. No short option.
+  bool no_fwd_decls;  // Disable forward declarations.
 };
 
 const CommandlineFlags& GlobalFlags();

iwyu_output.cc

@@ -874,6 +874,7 @@ set<string> CalculateMinimalIncludes(
 // A6) If any of the redeclarations of this declaration is in the same
 //     file as the use (and before it), and is actually a definition,
 //     discard the forward-declare use.
+// A7) If --no_fwd_decls has been passed, recategorize as a full use.
 
 // Trimming symbol uses (1st pass):
 // B1) If the definition of a full use comes after the use, change the
@@ -1032,6 +1033,11 @@ void ProcessForwardDeclare(OneUse* use,
       return;
     }
   }
+
+  // (A7) If --no_fwd_decls has been passed, recategorize as a full use.
+  if (GlobalFlags().no_fwd_decls) {
+    use->set_full_use();
+  }
 }
 
 void ProcessFullUse(OneUse* use,

run_iwyu_tests.py

@@ -76,6 +76,7 @@ class OneIwyuTest(unittest.TestCase):
                                     '--transitive_includes_only'],
       'no_h_includes_cc.cc': [self.CheckAlsoExtension('.c')],
       'no_comments.cc': ['--no_comments'],
+      'no_fwd_decls.cc': ['--no_fwd_decls'],
       'overloaded_class.cc': [self.CheckAlsoExtension('-i1.h')],
       'pch_in_code.cc': ['--pch_in_code', '--prefix_header_includes=remove'],
       'prefix_header_attribution.cc': ['--prefix_header_includes=remove'],
@@ -154,6 +155,7 @@ class OneIwyuTest(unittest.TestCase):
       'new_header_path_provided.cc': ['.'],
       'no_comments.cc': ['.'],
       'no_fwd_decl_nested_class.cc': ['.'],
+      'no_fwd_decls.cc': ['.'],
       'no_h_includes_cc.cc': ['.'],
       'non_transitive_include.cc': ['.'],
       'overloaded_class.cc': ['.'],

tests/cxx/no_fwd_decls.cc

@@ -0,0 +1,29 @@
+//===--- no_fwd_decls.cc - test input file for iwyu -----------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// Test that passing the --no_fwd_decls switch to IWYU suggests including the
+// corresponding header file even when the use is not a full use.
+
+#include "tests/cxx/direct.h"
+
+// IWYU: IndirectClass is...*indirect.h
+IndirectClass* global;
+
+/**** IWYU_SUMMARY
+
+tests/cxx/no_fwd_decls.cc should add these lines:
+#include "tests/cxx/indirect.h"
+
+tests/cxx/no_fwd_decls.cc should remove these lines:
+- #include "tests/cxx/direct.h"  // lines XX-XX
+
+The full include-list for tests/cxx/no_fwd_decls.cc:
+#include "tests/cxx/indirect.h"  // for IndirectClass
+
+***** IWYU_SUMMARY */