Coff linker: Add IMPLIB support

Allow --out-implib and -implib as passed by cmake and meson to be
correctly passed through to the linker to generate import libraries.

src/Compilation.zig

@@ -767,6 +767,8 @@ pub const InitOptions = struct {
     test_filter: ?[]const u8 = null,
     test_name_prefix: ?[]const u8 = null,
     subsystem: ?std.Target.SubSystem = null,
+    /// Windows/PE only. Where to output the import library, can contain directories.
+    out_implib: ?[]const u8 = null,
     /// WASI-only. Type of WASI execution model ("command" or "reactor").
     wasi_exec_model: ?std.builtin.WasiExecModel = null,
     /// (Zig compiler development) Enable dumping linker's state as JSON.
@@ -946,7 +948,8 @@ pub fn create(gpa: *Allocator, options: InitOptions) !*Compilation {
                 options.output_mode == .Lib or
                 options.lld_argv.len != 0 or
                 options.image_base_override != null or
-                options.linker_script != null or options.version_script != null)
+                options.linker_script != null or options.version_script != null or
+                options.out_implib != null)
             {
                 break :blk true;
             }
@@ -1461,6 +1464,7 @@ pub fn create(gpa: *Allocator, options: InitOptions) !*Compilation {
             .each_lib_rpath = options.each_lib_rpath orelse options.is_native_os,
             .disable_lld_caching = options.disable_lld_caching,
             .subsystem = options.subsystem,
+            .out_implib = options.out_implib,
             .is_test = options.is_test,
             .wasi_exec_model = wasi_exec_model,
             .use_stage1 = use_stage1,

src/link.zig

@@ -127,6 +127,7 @@ pub const Options = struct {
     gc_sections: ?bool = null,
     allow_shlib_undefined: ?bool,
     subsystem: ?std.Target.SubSystem,
+    out_implib: ?[]const u8,
     linker_script: ?[]const u8,
     version_script: ?[]const u8,
     soname: ?[]const u8,

src/link/Coff.zig

@@ -948,6 +948,7 @@ fn linkWithLLD(self: *Coff, comp: *Compilation) !void {
         man.hash.add(self.base.options.dynamicbase);
         man.hash.addOptional(self.base.options.major_subsystem_version);
         man.hash.addOptional(self.base.options.minor_subsystem_version);
+        man.hash.addOptionalBytes(self.base.options.out_implib);
 
         // We don't actually care whether it's a cache hit or miss; we just need the digest and the lock.
         _ = try man.hit();
@@ -1094,6 +1095,10 @@ fn linkWithLLD(self: *Coff, comp: *Compilation) !void {
             try argv.append(p);
         }
 
+        if (self.base.options.out_implib != null) {
+            try argv.append(try allocPrint(arena, "-IMPLIB:{s}.lib", .{full_out_path}));
+        }
+
         const resolved_subsystem: ?std.Target.SubSystem = blk: {
             if (self.base.options.subsystem) |explicit| break :blk explicit;
             switch (target.os.tag) {

src/main.zig

@@ -654,6 +654,7 @@ fn buildOutputType(
     var main_pkg_path: ?[]const u8 = null;
     var clang_preprocessor_mode: Compilation.ClangPreprocessorMode = .no;
     var subsystem: ?std.Target.SubSystem = null;
+    var out_implib: ?[]const u8 = null;
     var major_subsystem_version: ?u32 = null;
     var minor_subsystem_version: ?u32 = null;
     var wasi_exec_model: ?std.builtin.WasiExecModel = null;
@@ -1637,6 +1638,14 @@ fn buildOutputType(
                         fatal("unable to parse -current_version '{s}': {s}", .{ linker_args.items[i], @errorName(err) });
                     };
                     have_version = true;
+                } else if (mem.eql(u8, arg, "--out-implib") or
+                    mem.eql(u8, arg, "-implib"))
+                {
+                    i += 1;
+                    if (i >= linker_args.items.len) {
+                        fatal("expected linker arg after '{s}'", .{arg});
+                    }
+                    out_implib = linker_args.items[i];
                 } else {
                     warn("unsupported linker arg: {s}", .{arg});
                 }
@@ -2154,6 +2163,16 @@ fn buildOutputType(
         else => false,
     };
 
+    // Always output import libraries (.lib) when building for msvc to replicate
+    // `link` behavior. lld does not always output import libraries so on the
+    // gnu abi users must set out_implib.
+    if (output_mode == .Lib and emit_bin == .yes and target_info.target.abi == .msvc and out_implib == null) {
+        const emit_bin_ext = fs.path.extension(emit_bin.yes);
+        out_implib = try std.fmt.allocPrint(gpa, "{s}.lib", .{
+            emit_bin.yes[0 .. emit_bin.yes.len - emit_bin_ext.len],
+        });
+    }
+
     gimmeMoreOfThoseSweetSweetFileDescriptors();
 
     const comp = Compilation.create(gpa, .{
@@ -2263,6 +2282,7 @@ fn buildOutputType(
         .test_name_prefix = test_name_prefix,
         .disable_lld_caching = !have_enable_cache,
         .subsystem = subsystem,
+        .out_implib = out_implib,
         .wasi_exec_model = wasi_exec_model,
         .debug_compile_errors = debug_compile_errors,
         .enable_link_snapshots = enable_link_snapshots,
@@ -2661,6 +2681,15 @@ fn updateModule(gpa: *Allocator, comp: *Compilation, hook: AfterUpdateHook) !voi
 
                 _ = try cache_dir.updateFile(src_pdb_path, cwd, dst_pdb_path, .{});
             }
+
+            if (comp.bin_file.options.out_implib) |out_implib| {
+                const src_implib_path = try std.fmt.allocPrint(gpa, "{s}.lib", .{bin_sub_path});
+                defer gpa.free(src_implib_path);
+                if (std.fs.path.dirname(out_implib)) |implib_dir| {
+                    try cwd.makePath(implib_dir);
+                }
+                _ = try cache_dir.updateFile(src_implib_path, cwd, out_implib, .{});
+            }
         },
     }
 }