From 56376a8a384adc7a7f28011922561a8d9f596305 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <m@mitchellh.com>
Date: Fri, 24 Oct 2025 11:40:10 -0700
Subject: [PATCH] sgr: make C compat

---
 src/lib/union.zig      |   2 +-
 src/terminal/color.zig |  20 ++++++++
 src/terminal/sgr.zig   | 103 +++++++++++++++++++++++++++++++++++++----
 3 files changed, 114 insertions(+), 11 deletions(-)

diff --git a/src/lib/union.zig b/src/lib/union.zig
index 7e15aa84d..9fe5e999c 100644
--- a/src/lib/union.zig
+++ b/src/lib/union.zig
@@ -104,7 +104,7 @@ pub fn TaggedUnion(
                     @tagName(tag),
                     value: {
                         switch (@typeInfo(@TypeOf(v))) {
-                            .@"enum", .@"struct", .@"union" => if (@hasDecl(@TypeOf(v), "cval")) v.cval(),
+                            .@"enum", .@"struct", .@"union" => if (@hasDecl(@TypeOf(v), "cval")) break :value v.cval(),
                             else => {},
                         }
 
diff --git a/src/terminal/color.zig b/src/terminal/color.zig
index d108e205b..b71279dbb 100644
--- a/src/terminal/color.zig
+++ b/src/terminal/color.zig
@@ -68,6 +68,12 @@ pub const Name = enum(u8) {
     // Remainders are valid unnamed values in the 256 color palette.
     _,
 
+    pub const C = u8;
+
+    pub fn cval(self: Name) C {
+        return @intFromEnum(self);
+    }
+
     /// Default colors for tagged values.
     pub fn default(self: Name) !RGB {
         return switch (self) {
@@ -179,6 +185,20 @@ pub const RGB = packed struct(u24) {
     g: u8 = 0,
     b: u8 = 0,
 
+    pub const C = extern struct {
+        r: u8,
+        g: u8,
+        b: u8,
+    };
+
+    pub fn cval(self: RGB) C {
+        return .{
+            .r = self.r,
+            .g = self.g,
+            .b = self.b,
+        };
+    }
+
     pub fn eql(self: RGB, other: RGB) bool {
         return self.r == other.r and self.g == other.g and self.b == other.b;
     }
diff --git a/src/terminal/sgr.zig b/src/terminal/sgr.zig
index d589172ad..a345a7a90 100644
--- a/src/terminal/sgr.zig
+++ b/src/terminal/sgr.zig
@@ -1,26 +1,22 @@
 //! SGR (Select Graphic Rendition) attrinvbute parsing and types.
 
 const std = @import("std");
+const build_options = @import("terminal_options");
 const assert = std.debug.assert;
 const testing = std.testing;
+const lib = @import("../lib/main.zig");
 const color = @import("color.zig");
 const SepList = @import("Parser.zig").Action.CSI.SepList;
 
-/// Attribute type for SGR
-pub const Attribute = union(enum) {
-    pub const Tag = std.meta.FieldEnum(Attribute);
+const lib_target: lib.Target = if (build_options.c_abi) .c else .zig;
 
+/// Attribute type for SGR
+pub const Attribute = union(Tag) {
     /// Unset all attributes
     unset,
 
     /// Unknown attribute, the raw CSI command parameters are here.
-    unknown: struct {
-        /// Full is the full SGR input.
-        full: []const u16,
-
-        /// Partial is the remaining, where we got hung up.
-        partial: []const u16,
-    },
+    unknown: Unknown,
 
     /// Bold the text.
     bold,
@@ -85,6 +81,68 @@ pub const Attribute = union(enum) {
     /// Set foreground color as 256-color palette.
     @"256_fg": u8,
 
+    pub const Tag = lib.Enum(
+        lib_target,
+        &.{
+            "unset",
+            "unknown",
+            "bold",
+            "reset_bold",
+            "italic",
+            "reset_italic",
+            "faint",
+            "underline",
+            "reset_underline",
+            "underline_color",
+            "256_underline_color",
+            "reset_underline_color",
+            "overline",
+            "reset_overline",
+            "blink",
+            "reset_blink",
+            "inverse",
+            "reset_inverse",
+            "invisible",
+            "reset_invisible",
+            "strikethrough",
+            "reset_strikethrough",
+            "direct_color_fg",
+            "direct_color_bg",
+            "8_bg",
+            "8_fg",
+            "reset_fg",
+            "reset_bg",
+            "8_bright_bg",
+            "8_bright_fg",
+            "256_bg",
+            "256_fg",
+        },
+    );
+
+    pub const Unknown = struct {
+        /// Full is the full SGR input.
+        full: []const u16,
+
+        /// Partial is the remaining, where we got hung up.
+        partial: []const u16,
+
+        pub const C = extern struct {
+            full_ptr: [*]const u16,
+            full_len: usize,
+            partial_ptr: [*]const u16,
+            partial_len: usize,
+        };
+
+        pub fn cval(self: Unknown) Unknown.C {
+            return .{
+                .full_ptr = self.full.ptr,
+                .full_len = self.full.len,
+                .partial_ptr = self.partial.ptr,
+                .partial_len = self.partial.len,
+            };
+        }
+    };
+
     pub const Underline = enum(u3) {
         none = 0,
         single = 1,
@@ -92,7 +150,28 @@ pub const Attribute = union(enum) {
         curly = 3,
         dotted = 4,
         dashed = 5,
+
+        pub const C = u8;
+
+        pub fn cval(self: Underline) Underline.C {
+            return @intFromEnum(self);
+        }
     };
+
+    /// C ABI functions.
+    const c_union = lib.TaggedUnion(
+        lib_target,
+        @This(),
+        // Padding size for C ABI compatibility.
+        // Largest variant is Unknown.C: 2 pointers + 2 usize = 32 bytes on 64-bit.
+        // We use [8]u64 (64 bytes) to allow room for future expansion while
+        // maintaining ABI compatibility.
+        [8]u64,
+    );
+    pub const Value = c_union.Value;
+    pub const C = c_union.C;
+    pub const CValue = c_union.CValue;
+    pub const cval = c_union.cval;
 };
 
 /// Parser parses the attributes from a list of SGR parameters.
@@ -380,6 +459,10 @@ fn testParseColon(params: []const u16) Attribute {
     return p.next().?;
 }
 
+test "sgr: Attribute C compat" {
+    _ = Attribute.C;
+}
+
 test "sgr: Parser" {
     try testing.expect(testParse(&[_]u16{}) == .unset);
     try testing.expect(testParse(&[_]u16{0}) == .unset);