build: include zig.h when CompileStep.emit_h is true

lib/build_runner.zig

@@ -28,6 +28,10 @@ pub fn main() !void {
         std.debug.print("Expected path to zig compiler\n", .{});
         return error.InvalidArgs;
     };
+    const zig_lib_dir = nextArg(args, &arg_idx) orelse {
+        std.debug.print("Expected zig lib directory path\n", .{});
+        return error.InvalidArgs;
+    };
     const build_root = nextArg(args, &arg_idx) orelse {
         std.debug.print("Expected build root directory path\n", .{});
         return error.InvalidArgs;
@@ -46,6 +50,7 @@ pub fn main() !void {
     const builder = try std.Build.create(
         allocator,
         zig_exe,
+        zig_lib_dir,
         build_root,
         cache_root,
         global_cache_root,

lib/std/Build.zig

@@ -63,6 +63,7 @@ color: enum { auto, on, off } = .auto,
 reference_trace: ?u32 = null,
 invalid_user_input: bool,
 zig_exe: []const u8,
+zig_lib_dir: []const u8,
 default_step: *Step,
 env_map: *EnvMap,
 top_level_steps: ArrayList(*TopLevelStep),
@@ -185,6 +186,7 @@ pub const DirList = struct {
 pub fn create(
     allocator: Allocator,
     zig_exe: []const u8,
+    zig_lib_dir: []const u8,
     build_root: []const u8,
     cache_root: []const u8,
     global_cache_root: []const u8,
@@ -196,6 +198,7 @@ pub fn create(
     const self = try allocator.create(Build);
     self.* = Build{
         .zig_exe = zig_exe,
+        .zig_lib_dir = zig_lib_dir,
         .build_root = build_root,
         .cache_root = try fs.path.relative(allocator, build_root, cache_root),
         .global_cache_root = global_cache_root,
@@ -281,6 +284,7 @@ fn createChildOnly(parent: *Build, dep_name: []const u8, build_root: []const u8)
         .reference_trace = parent.reference_trace,
         .invalid_user_input = false,
         .zig_exe = parent.zig_exe,
+        .zig_lib_dir = parent.zig_exe,
         .default_step = undefined,
         .env_map = parent.env_map,
         .top_level_steps = ArrayList(*TopLevelStep).init(allocator),

lib/std/Build/CompileStep.zig

@@ -1630,6 +1630,10 @@ fn make(step: *Step) !void {
                     const h_path = other.getOutputHSource().getPath(builder);
                     try zig_args.append("-isystem");
                     try zig_args.append(fs.path.dirname(h_path).?);
+                    if (builder.zig_lib_dir.len > 0) {
+                        try zig_args.append("-isystem");
+                        try zig_args.append(builder.zig_lib_dir);
+                    }
                 }
                 if (other.installed_headers.items.len > 0) {
                     for (other.installed_headers.items) |install_step| {

src/main.zig

@@ -3936,6 +3936,9 @@ pub fn cmdBuild(gpa: Allocator, arena: Allocator, args: []const []const u8) !voi
 
         try child_argv.append(self_exe_path);
 
+        const argv_index_zig_lib_dir = child_argv.items.len;
+        _ = try child_argv.addOne();
+
         const argv_index_build_file = child_argv.items.len;
         _ = try child_argv.addOne();
 
@@ -4004,6 +4007,8 @@ pub fn cmdBuild(gpa: Allocator, arena: Allocator, args: []const []const u8) !voi
         };
         defer zig_lib_directory.handle.close();
 
+        child_argv.items[argv_index_zig_lib_dir] = zig_lib_directory.path orelse "";
+
         var cleanup_build_dir: ?fs.Dir = null;
         defer if (cleanup_build_dir) |*dir| dir.close();
 

test/standalone.zig

@@ -103,4 +103,5 @@ pub fn addCases(cases: *tests.StandaloneContext) void {
     cases.addBuildFile("test/standalone/emit_asm_and_bin/build.zig", .{});
     cases.addBuildFile("test/standalone/issue_12588/build.zig", .{});
     cases.addBuildFile("test/standalone/embed_generated_file/build.zig", .{});
+    cases.addBuildFile("test/standalone/c_exe_with_emit_h/build.zig", .{});
 }

test/standalone/c_exe_with_emit_h/build.zig

@@ -0,0 +1,29 @@
+const std = @import("std");
+
+pub fn build(b: *std.Build) void {
+    const optimize = b.standardOptimizeOption(.{});
+    const target = b.standardTargetOptions(.{});
+
+    const lib = b.addSharedLibrary(.{
+        .name = "math",
+        .root_source_file = .{ .path = "math.zig" },
+        .version = .{ .major = 1, .minor = 0, .patch = 0 },
+        .target = target,
+        .optimize = optimize,
+    });
+    lib.emit_h = true;
+
+    const exe = b.addExecutable(.{
+        .name = "main",
+    });
+    exe.addCSourceFile("main.c", &[_][]const u8{"-std=c99"});
+    exe.linkLibrary(lib);
+    exe.linkSystemLibrary("c");
+
+    b.default_step.dependOn(&exe.step);
+
+    const run_cmd = exe.run();
+
+    const test_step = b.step("test", "Test the program");
+    test_step.dependOn(&run_cmd.step);
+}

test/standalone/c_exe_with_emit_h/main.c

@@ -0,0 +1,11 @@
+// This header is generated by zig from math.zig
+#include "math.h"
+#include <stdio.h>
+
+int main(int argc, char **argv) {
+    int32_t result = add(42, 1337);
+    if (result != 1379) {
+	    return 1;
+    }
+    return 0;
+}

test/standalone/c_exe_with_emit_h/math.zig

@@ -0,0 +1,3 @@
+export fn add(a: i32, b: i32) i32 {
+    return a + b;
+}