std.Build.ConfigHeaderStep: support outputting assembly config files

lib/std/Build/ConfigHeaderStep.zig

@@ -13,11 +13,13 @@ pub const Style = union(enum) {
     cmake: std.Build.FileSource,
     /// Instead of starting with an input file, start with nothing.
     blank,
+    /// Start with nothing, like blank, and output a nasm .asm file.
+    nasm,
 
     pub fn getFileSource(style: Style) ?std.Build.FileSource {
         switch (style) {
             .autoconf, .cmake => |s| return s,
-            .blank => return null,
+            .blank, .nasm => return null,
         }
     }
 };
@@ -84,6 +86,10 @@ pub fn addValues(self: *ConfigHeaderStep, values: anytype) void {
     return addValuesInner(self, values) catch @panic("OOM");
 }
 
+pub fn getFileSource(self: *ConfigHeaderStep) std.Build.FileSource {
+    return .{ .generated = &self.output_file };
+}
+
 fn addValuesInner(self: *ConfigHeaderStep, values: anytype) !void {
     inline for (@typeInfo(@TypeOf(values)).Struct.fields) |field| {
         try putValue(self, field.name, field.type, @field(values, field.name));
@@ -164,22 +170,31 @@ fn make(step: *Step) !void {
     var output = std.ArrayList(u8).init(gpa);
     defer output.deinit();
 
-    try output.appendSlice("/* This file was generated by ConfigHeaderStep using the Zig Build System. */\n");
+    const header_text = "This file was generated by ConfigHeaderStep using the Zig Build System.";
+    const c_generated_line = "/* " ++ header_text ++ " */\n";
+    const asm_generated_line = "; " ++ header_text ++ "\n";
 
     switch (self.style) {
         .autoconf => |file_source| {
+            try output.appendSlice(c_generated_line);
             const src_path = file_source.getPath(self.builder);
             const contents = try std.fs.cwd().readFileAlloc(gpa, src_path, self.max_bytes);
             try render_autoconf(contents, &output, self.values, src_path);
         },
         .cmake => |file_source| {
+            try output.appendSlice(c_generated_line);
             const src_path = file_source.getPath(self.builder);
             const contents = try std.fs.cwd().readFileAlloc(gpa, src_path, self.max_bytes);
             try render_cmake(contents, &output, self.values, src_path);
         },
         .blank => {
+            try output.appendSlice(c_generated_line);
             try render_blank(&output, self.values, self.include_path);
         },
+        .nasm => {
+            try output.appendSlice(asm_generated_line);
+            try render_nasm(&output, self.values);
+        },
     }
 
     hash.update(output.items);
@@ -253,7 +268,7 @@ fn render_autoconf(
             any_errors = true;
             continue;
         };
-        try renderValue(output, name, kv.value);
+        try renderValueC(output, name, kv.value);
     }
 
     for (values_copy.keys()) |name| {
@@ -304,7 +319,7 @@ fn render_cmake(
             any_errors = true;
             continue;
         };
-        try renderValue(output, name, kv.value);
+        try renderValueC(output, name, kv.value);
     }
 
     for (values_copy.keys()) |name| {
@@ -338,7 +353,7 @@ fn render_blank(
 
     const values = defines.values();
     for (defines.keys()) |name, i| {
-        try renderValue(output, name, values[i]);
+        try renderValueC(output, name, values[i]);
     }
 
     try output.appendSlice("#endif /* ");
@@ -346,7 +361,14 @@ fn render_blank(
     try output.appendSlice(" */\n");
 }
 
-fn renderValue(output: *std.ArrayList(u8), name: []const u8, value: Value) !void {
+fn render_nasm(output: *std.ArrayList(u8), defines: std.StringArrayHashMap(Value)) !void {
+    const values = defines.values();
+    for (defines.keys()) |name, i| {
+        try renderValueNasm(output, name, values[i]);
+    }
+}
+
+fn renderValueC(output: *std.ArrayList(u8), name: []const u8, value: Value) !void {
     switch (value) {
         .undef => {
             try output.appendSlice("/* #undef ");
@@ -376,3 +398,33 @@ fn renderValue(output: *std.ArrayList(u8), name: []const u8, value: Value) !void
         },
     }
 }
+
+fn renderValueNasm(output: *std.ArrayList(u8), name: []const u8, value: Value) !void {
+    switch (value) {
+        .undef => {
+            try output.appendSlice("; %undef ");
+            try output.appendSlice(name);
+            try output.appendSlice("\n");
+        },
+        .defined => {
+            try output.appendSlice("%define ");
+            try output.appendSlice(name);
+            try output.appendSlice("\n");
+        },
+        .boolean => |b| {
+            try output.appendSlice("%define ");
+            try output.appendSlice(name);
+            try output.appendSlice(if (b) " 1\n" else " 0\n");
+        },
+        .int => |i| {
+            try output.writer().print("%define {s} {d}\n", .{ name, i });
+        },
+        .ident => |ident| {
+            try output.writer().print("%define {s} {s}\n", .{ name, ident });
+        },
+        .string => |string| {
+            // TODO: use nasm-specific escaping instead of zig string literals
+            try output.writer().print("%define {s} \"{}\"\n", .{ name, std.zig.fmtEscapes(string) });
+        },
+    }
+}