std.process: adding hasNonEmptyEnvVar() and using for NO_COLOR

lib/std/io/tty.zig

@@ -12,9 +12,9 @@ const native_os = builtin.os.tag;
 pub fn detectConfig(file: File) Config {
     const force_color: ?bool = if (builtin.os.tag == .wasi)
         null // wasi does not support environment variables
-    else if (process.hasEnvVarConstant("NO_COLOR"))
+    else if (process.hasNonEmptyEnvVarConstant("NO_COLOR"))
         false
-    else if (process.hasEnvVarConstant("CLICOLOR_FORCE"))
+    else if (process.hasNonEmptyEnvVarConstant("CLICOLOR_FORCE"))
         true
     else
         null;

lib/std/process.zig

@@ -431,6 +431,20 @@ pub fn hasEnvVarConstant(comptime key: []const u8) bool {
     }
 }
 
+/// On Windows, `key` must be valid UTF-8.
+pub fn hasNonEmptyEnvVarConstant(comptime key: []const u8) bool {
+    if (native_os == .windows) {
+        const key_w = comptime unicode.utf8ToUtf16LeStringLiteral(key);
+        const value = getenvW(key_w) orelse return false;
+        return value.len != 0;
+    } else if (native_os == .wasi and !builtin.link_libc) {
+        @compileError("hasNonEmptyEnvVarConstant is not supported for WASI without libc");
+    } else {
+        const value = posix.getenv(key) orelse return false;
+        return value.len != 0;
+    }
+}
+
 pub const ParseEnvVarIntError = std.fmt.ParseIntError || error{EnvironmentVariableNotFound};
 
 /// Parses an environment variable as an integer.
@@ -477,6 +491,27 @@ pub fn hasEnvVar(allocator: Allocator, key: []const u8) HasEnvVarError!bool {
     }
 }
 
+/// On Windows, if `key` is not valid [WTF-8](https://simonsapin.github.io/wtf-8/),
+/// then `error.InvalidWtf8` is returned.
+pub fn hasNonEmptyEnvVar(allocator: Allocator, key: []const u8) HasEnvVarError!bool {
+    if (native_os == .windows) {
+        var stack_alloc = std.heap.stackFallback(256 * @sizeOf(u16), allocator);
+        const stack_allocator = stack_alloc.get();
+        const key_w = try unicode.wtf8ToWtf16LeAllocZ(stack_allocator, key);
+        defer stack_allocator.free(key_w);
+        const value = getenvW(key_w) orelse return false;
+        return value.len != 0;
+    } else if (native_os == .wasi and !builtin.link_libc) {
+        var envmap = getEnvMap(allocator) catch return error.OutOfMemory;
+        defer envmap.deinit();
+        const value = envmap.getPtr(key) orelse return false;
+        return value.len != 0;
+    } else {
+        const value = posix.getenv(key) orelse return false;
+        return value.len != 0;
+    }
+}
+
 /// Windows-only. Get an environment variable with a null-terminated, WTF-16 encoded name.
 ///
 /// This function performs a Unicode-aware case-insensitive lookup using RtlEqualUnicodeString.

lib/std/zig.zig

@@ -697,6 +697,10 @@ pub const EnvVar = enum {
     XDG_CACHE_HOME,
     HOME,
 
+    pub fn isSet(comptime ev: EnvVar) bool {
+        return std.process.hasNonEmptyEnvVarConstant(@tagName(ev));
+    }
+
     pub fn get(ev: EnvVar, arena: std.mem.Allocator) !?[]u8 {
         if (std.process.getEnvVarOwned(arena, @tagName(ev))) |value| {
             return value;
@@ -709,11 +713,6 @@ pub const EnvVar = enum {
     pub fn getPosix(comptime ev: EnvVar) ?[:0]const u8 {
         return std.posix.getenvZ(@tagName(ev));
     }
-
-    pub fn isSet(ev: EnvVar, arena: std.mem.Allocator) !bool {
-        const value = try ev.get(arena) orelse return false;
-        return value.len != 0;
-    }
 };
 
 pub const SimpleComptimeReason = enum(u32) {

src/main.zig

@@ -826,9 +826,9 @@ fn buildOutputType(
     var listen: Listen = .none;
     var debug_compile_errors = false;
     var verbose_link = (native_os != .wasi or builtin.link_libc) and
-        try EnvVar.ZIG_VERBOSE_LINK.isSet(arena);
+        EnvVar.ZIG_VERBOSE_LINK.isSet();
     var verbose_cc = (native_os != .wasi or builtin.link_libc) and
-        try EnvVar.ZIG_VERBOSE_CC.isSet(arena);
+        EnvVar.ZIG_VERBOSE_CC.isSet();
     var verbose_air = false;
     var verbose_intern_pool = false;
     var verbose_generic_instances = false;
@@ -1006,9 +1006,9 @@ fn buildOutputType(
     // if set, default the color setting to .off or .on, respectively
     // explicit --color arguments will still override this setting.
     // Disable color on WASI per https://github.com/WebAssembly/WASI/issues/162
-    var color: Color = if (native_os == .wasi or try EnvVar.NO_COLOR.isSet(arena))
+    var color: Color = if (native_os == .wasi or EnvVar.NO_COLOR.isSet())
         .off
-    else if (try EnvVar.CLICOLOR_FORCE.isSet(arena))
+    else if (EnvVar.CLICOLOR_FORCE.isSet())
         .on
     else
         .auto;
@@ -4769,9 +4769,9 @@ fn cmdBuild(gpa: Allocator, arena: Allocator, args: []const []const u8) !void {
     var reference_trace: ?u32 = null;
     var debug_compile_errors = false;
     var verbose_link = (native_os != .wasi or builtin.link_libc) and
-        try EnvVar.ZIG_VERBOSE_LINK.isSet(arena);
+        EnvVar.ZIG_VERBOSE_LINK.isSet();
     var verbose_cc = (native_os != .wasi or builtin.link_libc) and
-        try EnvVar.ZIG_VERBOSE_CC.isSet(arena);
+        EnvVar.ZIG_VERBOSE_CC.isSet();
     var verbose_air = false;
     var verbose_intern_pool = false;
     var verbose_generic_instances = false;
@@ -4954,7 +4954,7 @@ fn cmdBuild(gpa: Allocator, arena: Allocator, args: []const []const u8) !void {
     }
 
     const work_around_btrfs_bug = native_os == .linux and
-        try EnvVar.ZIG_BTRFS_WORKAROUND.isSet(arena);
+        EnvVar.ZIG_BTRFS_WORKAROUND.isSet();
     const root_prog_node = std.Progress.start(.{
         .disable_printing = (color == .off),
         .root_name = "Compile Build Script",
@@ -5461,7 +5461,7 @@ fn jitCmd(
         fatal("unable to find self exe path: {s}", .{@errorName(err)});
     };
 
-    const optimize_mode: std.builtin.OptimizeMode = if (try EnvVar.ZIG_DEBUG_CMD.isSet(arena))
+    const optimize_mode: std.builtin.OptimizeMode = if (EnvVar.ZIG_DEBUG_CMD.isSet())
         .Debug
     else
         .ReleaseFast;
@@ -6976,7 +6976,7 @@ fn cmdFetch(
 
     const color: Color = .auto;
     const work_around_btrfs_bug = native_os == .linux and
-        try EnvVar.ZIG_BTRFS_WORKAROUND.isSet(arena);
+        EnvVar.ZIG_BTRFS_WORKAROUND.isSet();
     var opt_path_or_url: ?[]const u8 = null;
     var override_global_cache_dir: ?[]const u8 = try EnvVar.ZIG_GLOBAL_CACHE_DIR.get(arena);
     var debug_hash: bool = false;