[C++] Update ninja file only when necessary

As this feature is incomplete, this is enabled only with
--regen flag.

I decided not to use ninja's "generator" feature because we
cannot create appropriate regeneration rules for globs in
Android. There are some directory names which are also used
as target names (e.g., "cts"). Ninja tries to build such
targets to check if regeneration is necessary.

1 files changed, 16 insertions, 1 deletions

diff --git a/main.cc b/main.cc
index 5d44994..e8eafa1 100644
--- a/main.cc
+++ b/main.cc
@@ -18,6 +18,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
+#include <time.h>
 #include <unistd.h>
 
 #include "ast.h"
@@ -44,6 +45,7 @@
 static const char* g_makefile;
 static bool g_is_syntax_check_only;
 static bool g_generate_ninja;
+static bool g_regen;
 static const char* g_ninja_suffix;
 static const char* g_ninja_dir;
 static bool g_use_find_emulator;
@@ -91,6 +93,9 @@ static void ParseCommandLine(int argc, char* argv[],
       g_enable_stat_logs = true;
     } else if (!strcmp(arg, "--ninja")) {
       g_generate_ninja = true;
+    } else if (!strcmp(arg, "--regen")) {
+      // TODO: Make this default.
+      g_regen = true;
     } else if (!strcmp(arg, "--detect_android_echo")) {
       g_detect_android_echo = true;
     } else if (!strcmp(arg, "--error_on_env_change")) {
@@ -217,6 +222,16 @@ static void FillDefaultVars(const vector<StringPiece>& cl_vars, Vars* vars) {
 static int Run(const vector<Symbol>& targets,
                const vector<StringPiece>& cl_vars,
                const string& orig_args) {
+  if (g_generate_ninja && g_regen) {
+    if (!NeedsRegen(g_ninja_suffix, g_ninja_dir)) {
+      fprintf(stderr, "No need to regenerate ninja file\n");
+      return 0;
+    }
+  }
+
+  time_t start_time;
+  time(&start_time);
+
   MakefileCacheManager* cache_mgr = NewMakefileCacheManager();
 
   Vars* vars = new Vars();
@@ -270,7 +285,7 @@ static int Run(const vector<Symbol>& targets,
   if (g_generate_ninja) {
     ScopedTimeReporter tr("generate ninja time");
     GenerateNinja(g_ninja_suffix, g_ninja_dir, nodes, ev, !targets.empty(),
-                  orig_args);
+                  orig_args, start_time);
     return 0;
   }