v: add support for @OS, @CCOMPILER @BACKEND and @PLATFORM (#25174)

doc/docs.md

@@ -6138,6 +6138,10 @@ that are substituted at compile time:
 - `@BUILD_DATE` => replaced with the build date, for example '2024-09-13' .
 - `@BUILD_TIME` => replaced with the build time, for example '12:32:07' .
 - `@BUILD_TIMESTAMP` => replaced with the build timestamp, for example '1726219885' .
+- `@OS` => replaced with the OS type, for example 'linux' .
+- `@CCOMPILER` => replaced with the C compiler type, for example 'gcc' .
+- `@BACKEND` => replaced with current language backend, for example 'c' or 'golang' .
+- `@PLATFORM` => replaced with the platform type, for example 'amd64' .
 Note: `@BUILD_DATE`, `@BUILD_TIME`, `@BUILD_TIMESTAMP` represent times in the UTC timezone.
 By default, they are based on the current time of the compilation/build. They can be overridden
 by setting the environment variable `SOURCE_DATE_EPOCH`. That is also useful while making

vlib/v/checker/checker.v

@@ -4030,6 +4030,18 @@ fn (mut c Checker) at_expr(mut node ast.AtExpr) ast.Type {
 		.build_timestamp {
 			node.val = util.stable_build_time.unix().str()
 		}
+		.os {
+			node.val = pref.get_host_os().lower()
+		}
+		.ccompiler {
+			node.val = c.pref.ccompiler_type.str()
+		}
+		.backend {
+			node.val = c.pref.backend.str()
+		}
+		.platform {
+			node.val = c.pref.arch.str()
+		}
 		.unknown {
 			c.error('unknown @ identifier: ${node.name}. Available identifiers: ${token.valid_at_tokens}',
 				node.pos)

vlib/v/parser/comptime.v

@@ -511,6 +511,10 @@ fn (mut p Parser) at() ast.AtExpr {
 		'@BUILD_DATE' { token.AtKind.build_date }
 		'@BUILD_TIME' { token.AtKind.build_time }
 		'@BUILD_TIMESTAMP' { token.AtKind.build_timestamp }
+		'@OS' { token.AtKind.os }
+		'@CCOMPILER' { token.AtKind.ccompiler }
+		'@BACKEND' { token.AtKind.backend }
+		'@PLATFORM' { token.AtKind.platform }
 		else { token.AtKind.unknown }
 	}
 	expr := ast.AtExpr{

vlib/v/scanner/tests/unknown_comptime_var_err.out

@@ -5,4 +5,5 @@ vlib/v/scanner/tests/unknown_comptime_var_err.vv:2:9: error: @ must be used befo
     3 | }
 Details: available compile time variables: @VROOT, @VMODROOT, @VEXEROOT, @FN, @METHOD, @MOD,
 @STRUCT, @VEXE, @FILE, @DIR, @LINE, @COLUMN, @VHASH, @VCURRENTHASH, @VMOD_FILE, @VMODHASH,
-@FILE_LINE, @LOCATION, @BUILD_DATE, @BUILD_TIME, @BUILD_TIMESTAMP
+@FILE_LINE, @LOCATION, @BUILD_DATE, @BUILD_TIME, @BUILD_TIMESTAMP, @OS, @CCOMPILER,
+@BACKEND, @PLATFORM

vlib/v/tests/comptime/comptime_at_test.v

@@ -198,3 +198,27 @@ fn test_at_build_date_time_timestamp() {
 	now_utc := dump(time.utc().unix())
 	assert now_utc >= bts.i64()
 }
+
+fn test_at_os() {
+	println('Current OS is ${@OS}')
+	assert @OS in ['termux', 'android', 'wasm32_emscripten', 'linux', 'ios', 'macos', 'windows',
+		'freebsd', 'openbsd', 'netbsd', 'dragonfly', 'serenity', 'plan9', 'vinix', 'solaris', 'haiku',
+		'js_node', 'js_freestanding', 'js_browser']
+}
+
+fn test_at_ccompiler() {
+	println('Current C Compiler is ${@CCOMPILER}')
+	assert @CCOMPILER in ['gcc', 'tinyc', 'clang', 'emcc', 'mingw', 'msvc', 'cplusplus']
+}
+
+fn test_at_backend() {
+	println('Current language backend is ${@BACKEND}')
+	assert @BACKEND in ['c', 'golang', 'interpret', 'js_node', 'js_browser', 'js_freestanding',
+		'native', 'wasm']
+}
+
+fn test_at_platform() {
+	println('Current Platform is ${@PLATFORM}')
+	assert @PLATFORM in ['amd64', 'arm64', 'arm32', 'rv64', 'rv32', 'i386', 's390x', 'ppc64le',
+		'loongarch64', 'js_node', 'js_browser', 'js_freestanding', 'wasm32']
+}

vlib/v/token/token.v

@@ -189,6 +189,10 @@ pub enum AtKind {
 	build_date
 	build_time
 	build_timestamp
+	os
+	ccompiler
+	backend
+	platform
 }
 
 pub const assign_tokens = [Kind.assign, .decl_assign, .plus_assign, .minus_assign, .mult_assign,
@@ -197,7 +201,8 @@ pub const assign_tokens = [Kind.assign, .decl_assign, .plus_assign, .minus_assig
 
 pub const valid_at_tokens = ['@VROOT', '@VMODROOT', '@VEXEROOT', '@FN', '@METHOD', '@MOD', '@STRUCT',
 	'@VEXE', '@FILE', '@DIR', '@LINE', '@COLUMN', '@VHASH', '@VCURRENTHASH', '@VMOD_FILE',
-	'@VMODHASH', '@FILE_LINE', '@LOCATION', '@BUILD_DATE', '@BUILD_TIME', '@BUILD_TIMESTAMP']
+	'@VMODHASH', '@FILE_LINE', '@LOCATION', '@BUILD_DATE', '@BUILD_TIME', '@BUILD_TIMESTAMP', '@OS',
+	'@CCOMPILER', '@BACKEND', '@PLATFORM']
 
 pub const token_str = build_token_str()