Force coloured output on GCC and Clang

Signed-off-by: Antonin Décimo <antonin@tarides.com>

src/dune_rules/super_context.ml

@@ -13,13 +13,26 @@ let default_context_flags (ctx : Context.t) ~project =
     | Some false ->
       (Build.return cflags, Build.return cxxflags)
     | Some true ->
-      let c = cflags @ Ocaml_config.ocamlc_cppflags ctx.ocaml_config in
+      let colors ccomp_type acc =
+        match ccomp_type with
+        | Cxx_flags.Gcc
+        | Clang
+          when Lazy.force Ansi_color.stderr_supports_color ->
+          "-fdiagnostics-color=always" :: acc
+        | _ -> acc
+      in
+      let c =
+        let open Build.O in
+        let+ ccomp_type, _ = Cxx_flags.get_flags ctx.build_dir in
+        cflags @ Ocaml_config.ocamlc_cppflags ctx.ocaml_config
+        |> colors ccomp_type
+      in
       let cxx =
         let open Build.O in
-        let+ _, db_flags = Cxx_flags.get_flags ctx.build_dir in
-        db_flags @ cxxflags
+        let+ ccomp_type, db_flags = Cxx_flags.get_flags ctx.build_dir in
+        db_flags @ cxxflags |> colors ccomp_type
       in
-      (Build.return c, cxx)
+      (c, cxx)
   in
   Foreign_language.Dict.make ~c ~cxx
 

test/blackbox-tests/test-cases/c-flags-diagnostics-color.t/run.t

@@ -0,0 +1,166 @@
+Check that -fdiagnostics-color=always is added to :standard flag set
+and the :standard set only if and only if
+- Dune is running in a tty;
+- the compiler is GCC or Clang;
+- use_standard_c_and_cxx_flags is true.
+
+The compiler is detected using the command name, that may not be most
+portable way.
+
+  $ O_CC=$(ocamlc -config-var c_compiler)
+
+We also have to trick Dune into believing it's executed in a tty,
+otherwise it won't output colors!
+
+  $ function cc_supported() {
+  >   if [[ "${O_CC}" == *gcc || "${O_CC}" = "clang" ]]; then
+  >     echo "1";
+  >   else echo "0"; fi }
+
+  $ function build_isatty() {
+  >   if [[ "$(cc_supported)" = 1 ]]; then
+  >     echo "int isatty(int fd) { return 1; }" |
+  >       $(ocamlc -config-var native_c_compiler) -shared -ldl -o isatty-yes.so -xc -;
+  >     echo "int isatty(int fd) { return 0; }" |
+  >       $(ocamlc -config-var native_c_compiler) -shared -ldl -o isatty-no.so -xc -;
+  >   fi
+  > }
+
+  $ function env_isatty() {
+  >   local b=$1; shift;
+  >   if [[ "$(cc_supported)" = 1 ]]; then
+  >     env									\
+  >       TERM=not_dumb								\
+  >       "DYLD_INSERT_LIBRARIES=$PWD/isatty-$b.so"				\
+  >       DYLD_FORCE_FLAT_NAMESPACE=y						\
+  >       "LD_PRELOAD=$PWD/isatty-$b.so" 					\
+  >       "$@";
+  >   else
+  >     env "$@";
+  >   fi
+  > }
+
+tty /\ not (:standard) => not (-fdiagnostics-color)
+==================================
+
+The flag shouldn't be present in the command, as we only want it in
+the :standard set.
+
+  $ cat >dune-project <<EOF
+  > (lang dune 2.8)
+  > (use_standard_c_and_cxx_flags false)
+  > EOF
+  $ cat >dune <<EOF
+  > (library
+  >  (name test)
+  >  (foreign_stubs (language c) (names stub)))
+  > EOF
+
+  $ build_isatty
+  $ env_isatty yes dune rules -m stub.o | tr -s '\t\n\\' ' ' > out_stub
+
+  $ grep -ce "-fdiagnostics-color=always" out_stub
+  0
+  [1]
+
+tty /\ :standard => -fdiagnostics-color
+==================================
+
+The flag should be present in the command, as we want it in the
+:standard set.
+
+  $ cat >dune-project <<EOF
+  > (lang dune 2.8)
+  > (use_standard_c_and_cxx_flags true)
+  > EOF
+  $ cat >dune <<EOF
+  > (library
+  >  (name test)
+  >  (foreign_stubs (language c) (names stub)))
+  > EOF
+
+  $ build_isatty
+  $ env_isatty yes dune rules -m stub.o | tr -s '\t\n\\' ' ' > out_stub
+
+  $ out=$(grep -ce "-fdiagnostics-color=always" out_stub);
+  > if [[ "$(cc_supported)" = 1 ]]; then
+  >   echo $out;
+  > elif [ $out = 0 ]; then
+  >   echo 1;
+  > else
+  >   echo 0;
+  > fi
+  1
+
+tty /\ :standard /\ not (-fdiagnostics-color) => not (-fdiagnostics-color)
+==================================
+
+If the flag is disabled, it should never appear in the command line.
+
+  $ cat >dune-project <<EOF
+  > (lang dune 2.8)
+  > (use_standard_c_and_cxx_flags true)
+  > EOF
+  $ cat >dune <<EOF
+  > (library
+  >  (name test)
+  >  (foreign_stubs (language c) (names stub)
+  >   (flags :standard \ -fdiagnostics-color=always)))
+  > EOF
+
+  $ build_isatty
+  $ env_isatty yes dune rules -m stub.o | tr -s '\t\n\\' ' ' > out_stub
+
+  $ grep -ce "-fdiagnostics-color=always" out_stub
+  0
+  [1]
+
+not(tty) /\ :standard => not (-fdiagnostics-color)
+==================================
+
+If not running in a tty, the flag should not be present.
+
+  $ cat >dune-project <<EOF
+  > (lang dune 2.8)
+  > (use_standard_c_and_cxx_flags true)
+  > EOF
+  $ cat >dune <<EOF
+  > (library
+  >  (name test)
+  >  (foreign_stubs (language c) (names stub)))
+  > EOF
+
+  $ build_isatty
+  $ env_isatty no dune rules -m stub.o > out_stub
+
+  $ out=$(grep -ce "-fdiagnostics-color=always" out_stub);
+  > if [[ "$(cc_supported)" = 1 ]]; then
+  >   echo $out;
+  > elif [ $out = 0 ]; then
+  >   echo 1;
+  > else
+  >   echo 0;
+  > fi
+  0
+
+tty /\ :standard overridden => not (-fdiagnostics-color)
+==================================
+
+If the flag is disabled, it should never appear in the command line.
+
+  $ cat >dune-project <<EOF
+  > (lang dune 2.8)
+  > (use_standard_c_and_cxx_flags true)
+  > EOF
+  $ cat >dune <<EOF
+  > (library
+  >  (name test)
+  >  (foreign_stubs (language c) (names stub) (flags)))
+  > EOF
+
+  $ build_isatty
+  $ env_isatty yes dune rules -m stub.o | tr -s '\t\n\\' ' ' > out_stub
+
+  $ grep -ce "-fdiagnostics-color=always" out_stub
+  0
+  [1]

test/blackbox-tests/test-cases/c-flags-diagnostics-color.t/stub.c

@@ -0,0 +1 @@
+#error "error message"