gcc: Default Rust frontend to stdin when no input file is provided

This fixes an Internal Compiler Error (ICE) where the `crab1` frontend
would segmentation fault if run without any input source files.

gcc/ChangeLog:

	* rust/rust-lang.cc (grs_langhook_post_options): Set pfilename
	to "-" if no input file is provided and num_in_fnames is 0.
	* rust/rust-session-manager.cc (Session::handle_input_files):
	Handle num_files == 0 case explicitly by setting filename to "-".

Signed-off-by: shreyas-omkar <[email protected]>

Author: shreyas-omkar

gcc/rust/rust-lang.cc

@@ -110,6 +110,9 @@ grs_langhook_init (void)
 
   using_eh_for_cleanups ();
 
+  if (num_in_fnames == 0)
+    main_input_filename = "-";
+
   // initialise compiler session
   Rust::Session::get_instance ().init ();
 
@@ -286,6 +289,10 @@ grs_langhook_post_options (const char **pfilename ATTRIBUTE_UNUSED)
 {
   // can be used to override other options if required
 
+  // check for input file
+  if (!*pfilename && num_in_fnames == 0)
+    *pfilename = "-";
+
   // satisfies an assert in init_excess_precision in toplev.cc
   if (flag_excess_precision /*_cmdline*/ == EXCESS_PRECISION_DEFAULT)
     flag_excess_precision /*_cmdline*/ = EXCESS_PRECISION_STANDARD;

gcc/rust/rust-session-manager.cc

@@ -399,6 +399,12 @@ Session::enable_dump (std::string arg)
 void
 Session::handle_input_files (int num_files, const char **files)
 {
+  if (num_files == 0)
+    {
+      static const char *stdin_file[] = {"-"};
+      files = stdin_file;
+      num_files = 1;
+    }
   if (num_files != 1)
     rust_fatal_error (UNDEF_LOCATION,
 		      "only one file may be specified on the command line");