Use a better Xcode detection

Author: Frizlab

Sources/CLTLogger.swift

@@ -19,7 +19,7 @@ import Logging
  The idea is: “usable” text (text that is actually what the user asked for when launching your tool) should be output to stdout,
   presumably using `print`, the rest should be on stderr.
  If needed you can setup the logger to use any fd, the logger will simply `write(2)` to it.
- + Ouptut has special control chars for colors if program is not compiled w/ Xcode and output fd is a tty.
+ + Ouptut has special control chars for colors if the output fd is a tty and Xcode is not detected.
  You can force using or force not using colors.
  + If the write syscall fails, the log is lost (or partially lost; interrupts are retried; see SystemPackage for more info).
  + You can configure the logger not to automatically add a new line after each message.
@@ -141,7 +141,7 @@ public struct CLTLogger : LogHandler {
 		switch logPrefixStyle {
 			case .none:  constantsByLevel = [:]
 			case .text:  constantsByLevel = CLTLogger.defaultConstantsByLogLevelForText
-			case .emoji: constantsByLevel = CLTLogger.defaultConstantsByLogLevelForEmoji
+			case .emoji: constantsByLevel = CLTLogger.defaultConstantsByLogLevelForEmoji(on: fd)
 			case .color: constantsByLevel = CLTLogger.defaultConstantsByLogLevelForColors
 			case .auto: fatalError()
 		}
@@ -196,25 +196,35 @@ public struct CLTLogger : LogHandler {
 				case "color": return .color
 				case "emoji": return .emoji
 				case "text":  return .text
-				default: (/* nop: The logger style is invalid, we infer the style as if the variable is not there. */)
+				default: (/* nop: The logger style is invalid, we infer the style as if the variable were not there. */)
 			}
 		}
-		let supportsColor = {
-			if let s = getenv("__CFBundleIdentifier"), String(cString: s) == "com.apple.dt.Xcode" {
-				/* Xcode runs the programs in a tty, but does not support colors. */
-				return false
-			}
-			if isatty(fd.rawValue) != 0 {
-				/* TODO: Check whether the tty actually supports colors.
-				 * Hint: `tput colors` is able to return the numbers of colors supported in the terminal. How does it do it? */
-				return true
-			}
-			if let s = getenv("GITHUB_ACTIONS"), String(cString: s) == "true" {
-				return true
+		
+		/* * * The logging style is not defined specifically in the dedicated environment value: we try and detect a correct value depending on other environmental clues. * * */
+		
+		/* Is the fd on which we write a tty?
+		 * Most ttys nowadays support colors, with a notable exception: Xcode. */
+		if isatty(fd.rawValue) != 0 {
+			/* Xcode detection: it ain’t trivial.
+			 * I found checking for the existence of the __XCODE_BUILT_PRODUCTS_DIR_PATHS env var to be a possible solution.
+			 * We could also probably check for the existence of the TERM env var: Xcode does not set it.
+			 * (When Package.swift is built we can check if the value of the __CFBundleIdentifier env var is "com.apple.dt.Xcode".)
+			 * The solution we’re currently using is to check whether the fd on which we write has a foreground process group as Xcode does not set one. 
+			 * Note: If Xcode detection is changed here, it should also be changed in defaultConstantsByLogLevelForEmoji. */
+			if tcgetpgrp(fd.rawValue) == -1 && errno == ENOTTY {
+				/* We log using emojis in Xcode. */
+				return .emoji
 			}
-			return false
+			/* If the TERM env var is not set we assume colors are not supported and return the text logging style. 
+			 * In theory we should use the curses database to check for colors (ncurses has the `has_colors` function for this). */
+			return (getenv("TERM") == nil ? .text : .color)
 		}
-		return (supportsColor() ? .color : .emoji)
+		if let s = getenv("GITHUB_ACTIONS"), String(cString: s) == "true" {
+			/* GitHub does support colors. */
+			return .color
+		}
+		/* Unknown case: we return the text logging style. */
+		return .text
 	}
 
 	/* Do _not_ use os_unfair_lock, apparently it is bad in Swift:
@@ -254,17 +264,17 @@ public extension CLTLogger {
 		]
 	}()
 
-	static var defaultConstantsByLogLevelForEmoji: [Logger.Level: Constants] = {
+	static func defaultConstantsByLogLevelForEmoji(on fd: FileDescriptor) -> [Logger.Level: Constants] {
 		func addMeta(_ str: String, _ padding: String) -> Constants {
 			var str = str
-			if let s = getenv("__CFBundleIdentifier"), String(cString: s) == "com.apple.dt.Xcode" {
-				/* We’re in Xcode.
+			if isatty(fd.rawValue) != 0, tcgetpgrp(fd.rawValue) == -1, errno == ENOTTY {
+				/* We’re in Xcode (probably).
 				 * By default we do not do the emoji padding, unless explicitly asked to (`CLTLOGGER_TERMINAL_EMOJI` set to anything but “NO”). */
 				if let s = getenv("CLTLOGGER_TERMINAL_EMOJI"), String(cString: s) != "NO" {
 					str = str + padding
 				}
 			} else {
-				/* We’re not in Xcode.
+				/* We’re not in Xcode (probably).
 				 * By default we do the emoji padding, unless explicitly asked not to (`CLTLOGGER_TERMINAL_EMOJI` set to “NO”). */
 				if let s = getenv("CLTLOGGER_TERMINAL_EMOJI"), String(cString: s) == "NO" {
 					/*nop*/
@@ -291,7 +301,7 @@ public extension CLTLogger {
 			.error:    addMeta("❗️", ""),
 			.critical: addMeta("‼️", " ")
 		]
-	}()
+	}
 
 	/* Terminal does not support RGB colors, so we use 255-color palette. */
 	static var defaultConstantsByLogLevelForColors: [Logger.Level: Constants] = {