std: rework TTY detection and printing

This commit sketches an idea for how to deal with detection of file
streams as being terminals.

When a File stream is a terminal, writes through the stream should have
their escapes stripped unless the programmer explicitly enables terminal
escapes. Furthermore, the programmer needs a convenient API for
intentionally outputting escapes into the stream. In particular it
should be possible to set colors that are silently discarded when the
stream is not a terminal.

This commit makes `Io.File.Writer` track the terminal mode in the
already-existing `mode` field, making it the appropriate place to
implement escape stripping.

`Io.lockStderrWriter` returns a `*Io.File.Writer` with terminal
detection already done by default. This is a higher-level application
layer stream for writing to stderr.

Meanwhile, `std.debug.lockStderrWriter` also returns a `*Io.File.Writer`
but a lower-level one that is hard-coded to use a static single-threaded
`std.Io.Threaded` instance. This is the same instance that is used for
collecting debug information and iterating the unwind info.

1 files changed, 4 insertions, 4 deletions

diff --git a/lib/std/process.zig b/lib/std/process.zig
index f7ecf5fdc2..5c6e6f89eb 100644
--- a/lib/std/process.zig
+++ b/lib/std/process.zig
@@ -439,25 +439,25 @@ pub fn getEnvVarOwned(allocator: Allocator, key: []const u8) GetEnvVarOwnedError
 }
 
 /// On Windows, `key` must be valid WTF-8.
-pub fn hasEnvVarConstant(comptime key: []const u8) bool {
+pub inline fn hasEnvVarConstant(comptime key: []const u8) bool {
     if (native_os == .windows) {
         const key_w = comptime unicode.wtf8ToWtf16LeStringLiteral(key);
         return getenvW(key_w) != null;
     } else if (native_os == .wasi and !builtin.link_libc) {
-        @compileError("hasEnvVarConstant is not supported for WASI without libc");
+        return false;
     } else {
         return posix.getenv(key) != null;
     }
 }
 
 /// On Windows, `key` must be valid WTF-8.
-pub fn hasNonEmptyEnvVarConstant(comptime key: []const u8) bool {
+pub inline fn hasNonEmptyEnvVarConstant(comptime key: []const u8) bool {
     if (native_os == .windows) {
         const key_w = comptime unicode.wtf8ToWtf16LeStringLiteral(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");
+        return false;
     } else {
         const value = posix.getenv(key) orelse return false;
         return value.len != 0;