Extend -o to work when compiling C files

When using ocamlc/ocamlopt to compile C files, it was not possible
so far to control where the resulting object file should be written.

In other words, before this commit a command like

ocamlopt -c foo.c -o /tmp/foo.o

produced the following error message:

Options -c and -o are incompatible when compiling C files

This commit removes this restriction and lets the compiler accept
that the command-line options -c and -o are given simultaneously
also when compiling one C file, so that the previous command now works.

The -o command-line option remains forbidden when compiling several C files.

driver/compenv.ml

@@ -608,8 +608,13 @@ let process_action
   | ProcessCFile name ->
       readenv ppf (Before_compile name);
       Location.input_name := name;
-      if Ccomp.compile_file name <> 0 then raise (Exit_with_status 2);
-      ccobjs := c_object_of_filename name :: !ccobjs
+      let obj_name = match !output_name with
+        | None -> c_object_of_filename name
+        | Some n -> n
+      in
+      if Ccomp.compile_file ~output:obj_name name <> 0
+      then raise (Exit_with_status 2);
+      ccobjs := obj_name :: !ccobjs
   | ProcessObjects names ->
       ccobjs := names @ !ccobjs
   | ProcessDLLs names ->
@@ -656,12 +661,12 @@ let process_deferred_actions env =
   begin
     match final_output_name with
     | None -> ()
-    | Some output_name ->
+    | Some _output_name ->
         if !compile_only then begin
-          if List.filter (function
-              | ProcessCFile name -> c_object_of_filename name <> output_name
-              | _ -> false) !deferred_actions <> [] then
-            fatal "Options -c and -o are incompatible when compiling C files";
+          if List.length (List.filter (function
+              | ProcessCFile _ -> true
+              | _ -> false) !deferred_actions) > 1 then
+            fatal "Option -o makes no sense when compiling several C files";
 
           if List.length (List.filter (function
               | ProcessImplementation _

ocamltest/builtin_actions.ml

@@ -221,6 +221,29 @@ let check_program_output = make
     Builtin_variables.output
     Builtin_variables.reference)
 
+let file_exists_action _log env = 
+  match Environments.lookup Builtin_variables.file env with
+    | None -> 
+      let reason = reason_with_fallback env "the file variable is undefined" in
+      let result = Result.fail_with_reason reason in
+      (result, env)
+    | Some filename ->
+      if Sys.file_exists filename
+      then begin
+        let default_reason = Printf.sprintf "File %s exists" filename in
+        let reason = reason_with_fallback env default_reason in
+        let result = Result.pass_with_reason reason in
+        (result, env)
+      end else begin
+        let default_reason =
+          Printf.sprintf "File %s does not exist" filename
+        in
+        let reason = reason_with_fallback env default_reason in
+        let result = Result.fail_with_reason reason in
+        (result, env)
+      end
+let file_exists = make "file-exists" file_exists_action
+
 let initialize_test_exit_status_variables _log env =
   Environments.add_bindings
   [
@@ -263,5 +286,6 @@ let _ =
     arch_i386;
     arch_power;
     function_sections;
-    naked_pointers
+    naked_pointers;
+    file_exists;
   ]

ocamltest/builtin_actions.mli

@@ -47,3 +47,5 @@ val run : Actions.t
 val script : Actions.t
 
 val check_program_output : Actions.t
+
+val file_exists : Actions.t

ocamltest/builtin_variables.ml

@@ -34,6 +34,9 @@ let commandline = Variables.make ("commandline",
 let exit_status = Variables.make ("exit_status",
   "Expected program exit status")
 
+let file = Variables.make ("file",
+  "File whose existence should be tested")
+
 let files = Variables.make ("files",
   "Files used by the tests")
 
@@ -109,6 +112,7 @@ let _ = List.iter Variables.register_variable
     cwd;
     commandline;
     exit_status;
+    file;
     files;
     make;
     ocamltest_response;

ocamltest/builtin_variables.mli

@@ -25,6 +25,8 @@ val commandline : Variables.t
 
 val exit_status : Variables.t
 
+val file : Variables.t
+
 val files : Variables.t
 
 val make : Variables.t

testsuite/tests/tool-command-line/hello.c

@@ -0,0 +1,8 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int main()
+{
+  printf("Hello, world!\n");
+  return 0;
+}

testsuite/tests/tool-command-line/test-o-one-c-file.ml

@@ -0,0 +1,18 @@
+(* TEST
+files = "hello.c"
+* setup-ocamlopt.opt-build-env
+** script
+script = "mkdir outputdir"
+*** ocamlopt.opt
+all_modules = "hello.c"
+compile_only = "true"
+flags = "-o outputdir/hello.${objext}"
+**** file-exists
+file = "outputdir/hello.${objext}"
+*)
+
+(*
+  This test makes sure it is possible to specify the name of the output
+  object file when compiling a C file with the OCaml compiler.
+  The test does not need to contain any OCaml code.
+*)

testsuite/tests/tool-command-line/test-o-several-c-files.compilers.reference

@@ -0,0 +1 @@
+Option -o makes no sense when compiling several C files

testsuite/tests/tool-command-line/test-o-several-c-files.ml

@@ -0,0 +1,15 @@
+(* TEST
+* setup-ocamlopt.opt-build-env
+** ocamlopt.opt
+all_modules = "foo.c bar.c"
+compile_only = "true"
+flags = "-o outputdir/baz.${objext}"
+ocamlopt_opt_exit_status = "2"
+*** check-ocamlopt.opt-output
+*)
+
+(*
+  This test makes sure that the -o option is rejected when trying to
+  compile several C files during the same invocatin of the OCaml compiler.
+  The test does not need to contain any OCaml code.
+*)

testsuite/tests/tool-command-line/test.ml → testsuite/tests/tool-command-line/test-unknown-file.ml

@@ -28,4 +28,7 @@ compiler_output = "compiler-output"
 
 *)
 
-(* this file is just a test driver, the test does not contain real OCamlcode *)
+(*
+  This file is just a test driver, the test does not contain any
+  real OCaml code
+*)