gccrs: Add compiler driver

Our compiler driver is fairly simple so far. The key piece to enforce is
that a compilation unit in Rust is the whole crate, so the process for
compiling Rust means pointing the compiler at the main entry point such as
src/lib.rs or src/main.rs where the expansion pass takes over loading the
other source files to include them in the crate.

	gcc/rust/
	* rustspec.cc: New.

1 files changed, 191 insertions, 0 deletions

diff --git a/gcc/rust/rustspec.cc b/gcc/rust/rustspec.cc
new file mode 100644
index 00000000000..b05f8ae5454
--- /dev/null
+++ b/gcc/rust/rustspec.cc
@@ -0,0 +1,191 @@
+/* rustspec.c -- Specific flags and argument handling of the gcc Rust front end.
+   Copyright (C) 2009-2022 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "opts.h"
+
+// satisfy intellisense
+#include "options.h"
+
+/* This bit is set if we saw a `-xfoo' language specification.  */
+#define LANGSPEC (1 << 1)
+/* This bit is set if they did `-lc'.  */
+#define WITHLIBC (1 << 2)
+/* Skip this option.  */
+#define SKIPOPT (1 << 3)
+
+void
+lang_specific_driver (struct cl_decoded_option **in_decoded_options,
+		      unsigned int *in_decoded_options_count,
+		      int *in_added_libraries)
+{
+  unsigned int i, j;
+
+  /* The new argument list will be contained in this.  */
+  struct cl_decoded_option *new_decoded_options;
+
+  /* "-lc" if it appears on the command line.  */
+  const struct cl_decoded_option *saw_libc = 0;
+
+  /* An array used to flag each argument that needs a bit set for
+     LANGSPEC or WITHLIBC.  */
+  int *args;
+
+  /* True if we saw -static.  */
+  int static_link = 0;
+
+  /* True if we should add -shared-libgcc to the command-line.  */
+  int shared_libgcc = 1;
+
+  /* The total number of arguments with the new stuff.  */
+  unsigned int argc;
+
+  /* The argument list.  */
+  struct cl_decoded_option *decoded_options;
+
+  /* The number of libraries added in.  */
+  int added_libraries;
+
+  /* The total number of arguments with the new stuff.  */
+  int num_args = 1;
+
+  /* Whether the -o option was used.  */
+  bool saw_opt_o = false;
+
+  /* The first input file with an extension of .rs.  */
+  const char *first_rust_file = NULL;
+
+  argc = *in_decoded_options_count;
+  decoded_options = *in_decoded_options;
+  added_libraries = *in_added_libraries;
+
+  args = XCNEWVEC (int, argc);
+
+  for (i = 1; i < argc; i++)
+    {
+      const char *arg = decoded_options[i].arg;
+
+      switch (decoded_options[i].opt_index)
+	{
+	case OPT_l:
+	  if (strcmp (arg, "c") == 0)
+	    args[i] |= WITHLIBC;
+	  break;
+
+	case OPT_o:
+	  saw_opt_o = true;
+	  break;
+
+	case OPT_static:
+	  static_link = 1;
+	  break;
+
+	case OPT_static_libgcc:
+	  shared_libgcc = 0;
+	  break;
+
+	case OPT_SPECIAL_input_file:
+	  if (first_rust_file == NULL)
+	    {
+	      int len;
+
+	      len = strlen (arg);
+	      if (len > 3 && strcmp (arg + len - 3, ".rs") == 0)
+		first_rust_file = arg;
+	    }
+	  else
+	    {
+	      // FIXME: ARTHUR: Do we want to error here? If there's already one
+	      // file?
+	      // How do we error here? Do we want to instead just handle that in
+	      // the session manager?
+	    }
+
+	  break;
+	}
+    }
+
+    /* There's no point adding -shared-libgcc if we don't have a shared
+       libgcc.  */
+#ifndef ENABLE_SHARED_LIBGCC
+  shared_libgcc = 0;
+#endif
+
+  /* Make sure to have room for the trailing NULL argument.  */
+  num_args = argc + shared_libgcc * 5 + 10;
+  new_decoded_options = XNEWVEC (struct cl_decoded_option, num_args);
+
+  i = 0;
+  j = 0;
+
+  /* Copy the 0th argument, i.e., the name of the program itself.  */
+  new_decoded_options[j++] = decoded_options[i++];
+
+  /* NOTE: We start at 1 now, not 0.  */
+  while (i < argc)
+    {
+      new_decoded_options[j] = decoded_options[i];
+
+      if (!saw_libc && (args[i] & WITHLIBC))
+	{
+	  --j;
+	  saw_libc = &decoded_options[i];
+	}
+
+      if ((args[i] & SKIPOPT) != 0)
+	--j;
+
+      i++;
+      j++;
+    }
+
+  /* If we didn't see a -o option, add one.  This is because we need
+     the driver to pass all .rs files to rust1.  Without a -o option the
+     driver will invoke rust1 separately for each input file.  FIXME:
+     This should probably use some other interface to force the driver
+     to set combine_inputs.  */
+  if (!saw_opt_o)
+    {
+      generate_option (OPT_o, "a.out", 1, CL_DRIVER, &new_decoded_options[j]);
+      j++;
+    }
+
+  if (saw_libc)
+    new_decoded_options[j++] = *saw_libc;
+  if (shared_libgcc && !static_link)
+    generate_option (OPT_shared_libgcc, NULL, 1, CL_DRIVER,
+		     &new_decoded_options[j++]);
+
+  *in_decoded_options_count = j;
+  *in_decoded_options = new_decoded_options;
+  *in_added_libraries = added_libraries;
+}
+
+/* Called before linking.  Returns 0 on success and -1 on failure.  */
+int
+lang_specific_pre_link (void) /* Not used for Rust.  */
+{
+  return 0;
+}
+
+/* Number of extra output files that lang_specific_pre_link may generate.  */
+int lang_specific_extra_outfiles = 0; /* Not used for Rust.  */