v: support better separation of general Android vs Termux specific code (part 1)

cmd/v/help/build-c.txt

@@ -108,9 +108,11 @@ see also `v help build`.
 
       The compiler is known to also work, and has support for these operating
       systems also (although we do not test it as regularly as for the above):
-            `android`, `ios`,
+            `vinix`,
+            `ios`,
+            `android`, `termux`, 
             `freebsd`, `openbsd`, `netbsd`, `dragonfly`,
-            `solaris`, `serenity`, `haiku`, `vinix`,
+            `solaris`, `serenity`, `haiku`,
             `wasm32`, `wasm32-wasi`, `wasm32-emscripten`
 
       Note that V has the concept of platform files, i.e. files ending

vlib/os/os.v

@@ -317,6 +317,9 @@ pub fn get_raw_lines_joined() string {
 // user_os returns current user operating system name.
 pub fn user_os() string {
 	$if linux {
+		if getenv('TERMUX_VERSION') != '' {
+			return 'termux'
+		}
 		return 'linux'
 	}
 	$if macos {
@@ -340,6 +343,9 @@ pub fn user_os() string {
 	$if android {
 		return 'android'
 	}
+	// $if termux {
+	//	return 'termux'
+	// }
 	$if solaris {
 		return 'solaris'
 	}

vlib/v/checker/checker.v

@@ -24,8 +24,8 @@ const (
 
 pub const (
 	valid_comptime_if_os             = ['windows', 'ios', 'macos', 'mach', 'darwin', 'hpux', 'gnu',
-		'qnx', 'linux', 'freebsd', 'openbsd', 'netbsd', 'bsd', 'dragonfly', 'android', 'solaris',
-		'haiku', 'serenity', 'vinix']
+		'qnx', 'linux', 'freebsd', 'openbsd', 'netbsd', 'bsd', 'dragonfly', 'android', 'termux',
+		'solaris', 'haiku', 'serenity', 'vinix']
 	valid_comptime_compression_types = ['none', 'zlib']
 	valid_comptime_if_compilers      = ['gcc', 'tinyc', 'clang', 'mingw', 'msvc', 'cplusplus']
 	valid_comptime_if_platforms      = ['amd64', 'i386', 'aarch64', 'arm64', 'arm32', 'rv64', 'rv32']

vlib/v/doc/doc.v

@@ -39,6 +39,7 @@ pub enum Platform {
 	dragonfly
 	js // for interoperability in prefs.OS
 	android
+	termux // like android, but note that termux is running on devices natively, not cross compiling from other platforms
 	solaris
 	serenity
 	vinix
@@ -64,6 +65,7 @@ pub fn platform_from_string(platform_str string) ?Platform {
 		'serenity' { return .serenity }
 		'vinix' { return .vinix }
 		'android' { return .android }
+		'termux' { return .termux }
 		'haiku' { return .haiku }
 		'nix' { return .linux }
 		'' { return .auto }

vlib/v/gen/c/comptime.v

@@ -636,6 +636,10 @@ fn (mut g Gen) comptime_if_to_ifdef(name string, is_comptime_optional bool) ?str
 		'android' {
 			return '__ANDROID__'
 		}
+		'termux' {
+			// Note: termux is running on Android natively
+			return '__ANDROID__'
+		}
 		'solaris' {
 			return '__sun'
 		}

vlib/v/pref/os.v

@@ -3,6 +3,8 @@
 // that can be found in the LICENSE file.
 module pref
 
+import os
+
 pub enum OS {
 	_auto // Reserved so .macos cannot be misunderstood as auto
 	ios
@@ -17,6 +19,7 @@ pub enum OS {
 	js_browser
 	js_freestanding
 	android
+	termux // like android, but compiling/running natively on the devices
 	solaris
 	serenity
 	vinix
@@ -47,6 +50,7 @@ pub fn os_from_string(os_str string) ?OS {
 		'serenity' { return .serenity }
 		'vinix' { return .vinix }
 		'android' { return .android }
+		'termux' { return .termux }
 		'haiku' { return .haiku }
 		'raw' { return .raw }
 		'nix' { return .linux }
@@ -75,6 +79,7 @@ pub fn (o OS) str() string {
 		.js_freestanding { return 'JavaScript' }
 		.js_browser { return 'JavaScript(Browser)' }
 		.android { return 'Android' }
+		.termux { return 'Termux' }
 		.solaris { return 'Solaris' }
 		.serenity { return 'SerenityOS' }
 		.vinix { return 'Vinix' }
@@ -88,10 +93,13 @@ pub fn (o OS) str() string {
 }
 
 pub fn get_host_os() OS {
+	$if linux {
 		$if android {
+			if os.getenv('TERMUX_VERSION') != '' {
+				return .termux
+			}
 			return .android
 		}
-	$if linux {
 		return .linux
 	}
 	$if ios {

vlib/v/pref/should_compile.v

@@ -121,6 +121,10 @@ fn fname_without_platform_postfix(file string) string {
 		'_',
 		'android.c.v',
 		'_',
+		'termux.c.v',
+		'_',
+		'android_outside_termux.c.v',
+		'_',
 		'freebsd.c.v',
 		'_',
 		'openbsd.c.v',
@@ -178,10 +182,6 @@ pub fn (prefs &Preferences) should_compile_c(file string) bool {
 	if prefs.os != .ios && (file.ends_with('_ios.c.v') || file.ends_with('_ios.v')) {
 		return false
 	}
-	//
-	if prefs.os != .android && file.ends_with('_android.c.v') {
-		return false
-	}
 	if prefs.os != .freebsd && file.ends_with('_freebsd.c.v') {
 		return false
 	}
@@ -203,6 +203,30 @@ pub fn (prefs &Preferences) should_compile_c(file string) bool {
 	if prefs.os != .vinix && file.ends_with('_vinix.c.v') {
 		return false
 	}
+	if prefs.os in [.android, .termux] {
+		// Note: Termux is running natively on Android devices, but the compilers there (clang) usually do not have access
+		// to the Android SDK. The code here ensures that you can have `_termux.c.v` and `_android_outside_termux.c.v` postfixes,
+		// to target both the cross compilation case (where the SDK headers are used and available), and the Termux case,
+		// where the Android SDK is not used.
+		if file.ends_with('_android.c.v') {
+			// common case, should compile for both cross android and termux
+			// eprintln('prefs.os: $prefs.os | file: $file | common')
+			return true
+		}
+		if file.ends_with('_android_outside_termux.c.v') {
+			// compile code that targets Android, but NOT Termux (i.e. the SDK is available)
+			// eprintln('prefs.os: $prefs.os | file: $file | android_outside_termux')
+			return prefs.os == .android
+		}
+		if file.ends_with('_termux.c.v') {
+			// compile Termux specific code
+			// eprintln('prefs.os: $prefs.os | file: $file | termux specific')
+			return prefs.os == .termux
+		}
+	} else if file.ends_with('_android.c.v') || file.ends_with('_termux.c.v')
+		|| file.ends_with('_android_outside_termux.c.v') {
+		return false
+	}
 	return true
 }