Close BuildLog while running generators, fix #1724

While #1780 delayed opening .ninja_log until the first write, this
this didn't fully fix the issue on Windows: There might be build
statements which run before the generator resulting in an actual write
to .ninja_log.

To fix this once and for all the BuildLog now gets closed before running
the generator. BuildLog::log_file_path_ won't be cleared so that it can
be opened again after the generator finished.

1 files changed, 1 insertions, 2 deletions

diff --git a/src/build_log.cc b/src/build_log.cc
index e5f179c..c261b20 100644
--- a/src/build_log.cc
+++ b/src/build_log.cc
@@ -181,7 +181,7 @@ void BuildLog::Close() {
 }
 
 bool BuildLog::OpenForWriteIfNeeded() {
-  if (log_file_path_.empty()) {
+  if (log_file_ || log_file_path_.empty()) {
     return true;
   }
   log_file_ = fopen(log_file_path_.c_str(), "ab");
@@ -200,7 +200,6 @@ bool BuildLog::OpenForWriteIfNeeded() {
       return false;
     }
   }
-  log_file_path_.clear();
   return true;
 }