Add color output in SourceErrorHandler (#517)

This is currently only supported where VT100 escape sequences work. We
assume that if `isatty` is true then color will be supported. This logic will
likely need to be improved, but this is a good start. 

This PR also adds support for passing an environment variable to a test
via `ENV`. This is used to test the `FORCE_COLOR` environment variable.

1 files changed, 84 insertions, 0 deletions

diff --git a/src/color.cc b/src/color.cc
new file mode 100644
index 00000000..f1657728
--- /dev/null
+++ b/src/color.cc
@@ -0,0 +1,84 @@
+/*
+ * Copyright 2017 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "color.h"
+
+#include <cstdlib>
+
+#include "common.h"
+
+#if _WIN32
+#include <io.h>
+#include <windows.h>
+#elif HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
+namespace wabt {
+
+Color::Color(FILE* file, bool enabled) : file_(file) {
+  enabled_ = enabled && SupportsColor(file_);
+}
+
+// static
+bool Color::SupportsColor(FILE* file) {
+  char* force = getenv("FORCE_COLOR");
+  if (force) {
+    return atoi(force) != 0;
+  }
+
+#if _WIN32
+
+  {
+#if HAVE_WIN32_VT100
+    HANDLE handle;
+    if (file == stdout) {
+      handle = GetStdHandle(STD_OUTPUT_HANDLE);
+    } else if (file == stderr) {
+      handle = GetStdHandle(STD_ERROR_HANDLE);
+    } else {
+      return false;
+    }
+    DWORD mode;
+    if (!_isatty(_fileno(file)) || !GetConsoleMode(handle, mode) ||
+        !SetConsoleMode(handle, mode | ENABLE_VIRTUAL_TERMINAL_PROCESSING)) {
+      return false;
+    }
+    return true;
+#else
+    // TODO(binji): Support older Windows by using SetConsoleTextAttribute?
+    return false;
+#endif
+  }
+
+#elif HAVE_UNISTD_H
+
+  return isatty(fileno(file));
+
+#else
+
+  return false;
+
+#endif
+}
+
+void Color::WriteCode(const char* code) const {
+  if (enabled_) {
+    fputs(code, file_);
+  }
+}
+
+}  // namespace wabt