added auto-detection logic for console colour output (#817)

Add auto-detection of colour support to `AnsicolourStdoutSink`.

**New `colorMode` enum** (`On`, `Off`, `Auto`) added to the header, accepted by the `AnsicolorStdoutSink` constructor. Defaults to `Auto`, so all existing call sites are unaffected.

**`Auto` mode detection logic** (in `IscolourTerminal()`):

1. **TTY check** -- if stdout is not a terminal, colour is disabled.
2. **`NO_COLOR`** -- respects the no-colour.org convention. If set, colour is disabled.
3. **`COLORTERM`** -- if set (e.g. `truecolour`, `24bit`), colour is enabled.
4. **`TERM`** -- rejects `dumb`; accepts known colour-capable terminals via substring match:
   `alacritty`, `ansi`, `colour`, `console`, `cygwin`, `gnome`, `konsole`, `kterm`, `linux`, `msys`, `putty`, `rxvt`, `screen`, `tmux`, `vt100`, `vt102`, `xterm`.
   Substring matching covers variants like `xterm-256color` and `rxvt-unicode`.
5. **Fallback** -- Windows defaults to colour enabled (modern console supports ANSI natively); other platforms default to disabled.

When colour is disabled, ANSI escape sequences are omitted entirely from the output.

NOTE: this doesn't currently apply to all paths which do logging in zen as they may be determining their colour output mode separately from `AnsicolorStdoutSink`.

2 files changed, 107 insertions, 5 deletions

diff --git a/src/zencore/include/zencore/logging/ansicolorsink.h b/src/zencore/include/zencore/logging/ansicolorsink.h
index 9f859e8d7..5060a8393 100644
--- a/src/zencore/include/zencore/logging/ansicolorsink.h
+++ b/src/zencore/include/zencore/logging/ansicolorsink.h
@@ -8,10 +8,17 @@
 
 namespace zen::logging {
 
+enum class ColorMode
+{
+	On,
+	Off,
+	Auto
+};
+
 class AnsiColorStdoutSink : public Sink
 {
 public:
-	AnsiColorStdoutSink();
+	explicit AnsiColorStdoutSink(ColorMode Mode = ColorMode::Auto);
 	~AnsiColorStdoutSink() override;
 
 	void Log(const LogMessage& Msg) override;
diff --git a/src/zencore/logging/ansicolorsink.cpp b/src/zencore/logging/ansicolorsink.cpp
index 9b9959862..540d22359 100644
--- a/src/zencore/logging/ansicolorsink.cpp
+++ b/src/zencore/logging/ansicolorsink.cpp
@@ -5,8 +5,19 @@
 #include <zencore/logging/messageonlyformatter.h>
 
 #include <cstdio>
+#include <cstdlib>
 #include <mutex>
 
+#if defined(_WIN32)
+#	include <io.h>
+#	define ZEN_ISATTY _isatty
+#	define ZEN_FILENO _fileno
+#else
+#	include <unistd.h>
+#	define ZEN_ISATTY isatty
+#	define ZEN_FILENO fileno
+#endif
+
 namespace zen::logging {
 
 // Default formatter replicating spdlog's %+ pattern:
@@ -98,7 +109,90 @@ GetColorForLevel(LogLevel InLevel)
 
 struct AnsiColorStdoutSink::Impl
 {
-	Impl() : m_Formatter(std::make_unique<DefaultConsoleFormatter>()) {}
+	explicit Impl(ColorMode Mode) : m_Formatter(std::make_unique<DefaultConsoleFormatter>()), m_UseColor(ResolveColorMode(Mode)) {}
+
+	static bool IsColorTerminal()
+	{
+		// If stdout is not a TTY, no color
+		if (ZEN_ISATTY(ZEN_FILENO(stdout)) == 0)
+		{
+			return false;
+		}
+
+		// NO_COLOR convention (https://no-color.org/)
+		if (std::getenv("NO_COLOR") != nullptr)
+		{
+			return false;
+		}
+
+		// COLORTERM is set by terminals that support color (e.g. "truecolor", "24bit")
+		if (std::getenv("COLORTERM") != nullptr)
+		{
+			return true;
+		}
+
+		// Check TERM for known color-capable values
+		const char* Term = std::getenv("TERM");
+		if (Term != nullptr)
+		{
+			std::string_view TermView(Term);
+			// "dumb" terminals do not support color
+			if (TermView == "dumb")
+			{
+				return false;
+			}
+			// Match against known color-capable terminal types.
+			// TERM often includes suffixes like "-256color", so we use substring matching.
+			constexpr std::string_view ColorTerms[] = {
+				"alacritty",
+				"ansi",
+				"color",
+				"console",
+				"cygwin",
+				"gnome",
+				"konsole",
+				"kterm",
+				"linux",
+				"msys",
+				"putty",
+				"rxvt",
+				"screen",
+				"tmux",
+				"vt100",
+				"vt102",
+				"xterm",
+			};
+			for (std::string_view Candidate : ColorTerms)
+			{
+				if (TermView.find(Candidate) != std::string_view::npos)
+				{
+					return true;
+				}
+			}
+		}
+
+#if defined(_WIN32)
+		// Windows console supports ANSI color by default in modern versions
+		return true;
+#else
+		// Unknown terminal — be conservative
+		return false;
+#endif
+	}
+
+	static bool ResolveColorMode(ColorMode Mode)
+	{
+		switch (Mode)
+		{
+			case ColorMode::On:
+				return true;
+			case ColorMode::Off:
+				return false;
+			case ColorMode::Auto:
+			default:
+				return IsColorTerminal();
+		}
+	}
 
 	void Log(const LogMessage& Msg)
 	{
@@ -107,7 +201,7 @@ struct AnsiColorStdoutSink::Impl
 		MemoryBuffer Formatted;
 		m_Formatter->Format(Msg, Formatted);
 
-		if (Msg.ColorRangeEnd > Msg.ColorRangeStart)
+		if (m_UseColor && Msg.ColorRangeEnd > Msg.ColorRangeStart)
 		{
 			// Print pre-color range
 			fwrite(Formatted.data(), 1, Msg.ColorRangeStart, m_File);
@@ -148,10 +242,11 @@ struct AnsiColorStdoutSink::Impl
 private:
 	std::mutex				   m_Mutex;
 	std::unique_ptr<Formatter> m_Formatter;
-	FILE*					   m_File = stdout;
+	FILE*					   m_File	  = stdout;
+	bool					   m_UseColor = true;
 };
 
-AnsiColorStdoutSink::AnsiColorStdoutSink() : m_Impl(std::make_unique<Impl>())
+AnsiColorStdoutSink::AnsiColorStdoutSink(ColorMode Mode) : m_Impl(std::make_unique<Impl>(Mode))
 {
 }