[ELF] Implement --color-diagnostics

elf/cmdline.cc

@@ -55,7 +55,9 @@ static const char helpmsg[] = R"(
                               Generate build ID
     --no-build-id
   --chroot DIR                Set a given path to root directory
-  --color-diagnostics         Ignored
+  --color-diagnostics=[auto,always,never]
+                              Use colors in diagnostics
+  --color-diagnostics         Alias for --color-diagnostics=always
   --compress-debug-sections [none,zlib,zlib-gabi,zlib-gnu]
                               Compress .debug_* sections
   --demangle                  Demangle C++ symbols in log messages (default)
@@ -376,6 +378,7 @@ void parse_nonpositional_args(Context<E> &ctx,
   args = args.subspan(1);
 
   bool version_shown = false;
+  ctx.arg.color_diagnostics = isatty(STDERR_FILENO);
 
   while (!args.empty()) {
     std::string_view arg;
@@ -528,6 +531,20 @@ void parse_nonpositional_args(Context<E> &ctx,
       ctx.arg.directory = arg;
     } else if (read_arg(ctx, args, arg, "chroot")) {
       ctx.arg.chroot = arg;
+    } else if (args[0] == "-color-diagnostics=auto" ||
+               args[0] == "--color-diagnostics=auto") {
+      ctx.arg.color_diagnostics = isatty(STDERR_FILENO);
+      args = args.subspan(1);
+    } else if (args[0] == "-color-diagnostics=always" ||
+               args[0] == "--color-diagnostics=always") {
+      ctx.arg.color_diagnostics = true;
+      args = args.subspan(1);
+    } else if (args[0] == "-color-diagnostics=never" ||
+               args[0] == "--color-diagnostics=never") {
+      ctx.arg.color_diagnostics = false;
+      args = args.subspan(1);
+    } else if (read_flag(args, "color-diagnostics")) {
+      ctx.arg.color_diagnostics = true;
     } else if (read_flag(args, "warn-common")) {
       ctx.arg.warn_common = true;
     } else if (read_flag(args, "no-warn-common")) {

elf/mold.h

@@ -1219,6 +1219,7 @@ struct Context {
     bool Bsymbolic = false;
     bool Bsymbolic_functions = false;
     bool allow_multiple_definition = false;
+    bool color_diagnostics = false;
     bool demangle = true;
     bool discard_all = false;
     bool discard_locals = false;

macho/mold.h

@@ -766,6 +766,7 @@ struct Context {
   struct {
     bool ObjC = false;
     bool adhoc_codesign = true;
+    bool color_diagnostics = false;
     bool dead_strip = true;
     bool dead_strip_dylibs = false;
     bool deduplicate = true;

mold.h

@@ -102,7 +102,11 @@ template <typename C>
 class Error {
 public:
   Error(C &ctx) : out(ctx, std::cerr) {
-    out << "mold: ";
+    if (ctx.arg.color_diagnostics)
+      out << "mold: \033[0;1;31merror:\033[0m ";
+    else
+      out << "mold: error: ";
+
     ctx.has_error = true;
   }
 
@@ -119,9 +123,18 @@ template <typename C>
 class Warn {
 public:
   Warn(C &ctx) : out(ctx, std::cerr) {
-    out << "mold: ";
-    if (ctx.arg.fatal_warnings)
+    if (ctx.arg.fatal_warnings) {
+      if (ctx.arg.color_diagnostics)
+        out << "mold: \033[0;1;31merror:\033[0m ";
+      else
+        out << "mold: error: ";
       ctx.has_error = true;
+    } else {
+      if (ctx.arg.color_diagnostics)
+        out << "mold: \033[0;1;35warning:\033[0m ";
+      else
+        out << "mold: warning: ";
+    }
   }
 
   template <class T> Warn &operator<<(T &&val) {

test/elf/color-diagnostics.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+export LANG=
+set -e
+cd $(dirname $0)
+mold=`pwd`/../../mold
+echo -n "Testing $(basename -s .sh $0) ... "
+t=$(pwd)/../../out/test/elf/$(basename -s .sh $0)
+mkdir -p $t
+
+cat <<EOF | cc -o $t/a.o -c -xc -
+int foo();
+int main() { foo(); }
+EOF
+
+! $mold -o $t/exe $t/a.o --color-diagnostics 2> $t/log
+grep -Pq '\e' $t/log
+
+! $mold -o $t/exe $t/a.o --color-diagnostics=always 2> $t/log
+grep -Pq '\e' $t/log
+
+! $mold -o $t/exe $t/a.o --color-diagnostics=never 2> $t/log
+! grep -Pq '\e' $t/log || false
+
+! $mold -o $t/exe $t/a.o --color-diagnostics=auto 2> $t/log
+! grep -Pq '\e' $t/log || false
+
+echo OK