Add TraceMe() to main()

On POSIX systems, you may set CQUERY_TRACEME=1 before running your editor.
cquery will inherit that environment variable and stop itself at the start of main().

src/command_line.cc

@@ -383,6 +383,8 @@ void LanguageServerMain(const std::string& bin_name,
 // MAIN ////////////////////////////////////////////////////////////////////////
 ////////////////////////////////////////////////////////////////////////////////
 int main(int argc, char** argv) {
+  TraceMe();
+
   std::unordered_map<std::string, std::string> options =
       ParseOptions(argc, argv);
 

src/platform.h

@@ -48,3 +48,5 @@ void FreeUnusedMemory();
 
 // If true objective-c index tests will be run.
 bool RunObjectiveCIndexTests();
+
+void TraceMe();

src/platform_posix.cc

@@ -37,8 +37,11 @@
 #if defined(__FreeBSD__)
 #include <sys/param.h>   // MAXPATHLEN
 #include <sys/sysctl.h>  // sysctl
+#elif defined(__APPLE__) || defined(__BSD__)
+#include <sys/ptrace.h>
 #elif defined(__linux__)
 #include <malloc.h>
+#include <sys/ptrace.h>
 #endif
 
 #include <iostream>
@@ -272,4 +275,12 @@ bool RunObjectiveCIndexTests() {
 #endif
 }
 
+void TraceMe() {
+  // If the environment variable is defined, wait for a debugger.
+  // In gdb, you need to invoke `signal SIGCONT` if you want cquery to continue
+  // after detaching.
+  if (getenv("CQUERY_TRACEME"))
+    raise(SIGTSTP);
+}
+
 #endif

src/platform_win.cc

@@ -146,4 +146,8 @@ bool RunObjectiveCIndexTests() {
   return false;
 }
 
+// TODO Wait for debugger to attach
+void TraceMe() {
+}
+
 #endif