From 34f88722cd6c206cbbc312377563340f3c3ab2b2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Fri, 5 Dec 2025 07:25:51 +0100
Subject: [PATCH] compiler: support --dependency-file linker option

closes https://github.com/ziglang/zig/issues/22213
---
 src/Compilation.zig | 50 +++++++++++++++++++++++++++++++++++++++++++++
 src/main.zig        |  4 ++++
 2 files changed, 54 insertions(+)

diff --git a/src/Compilation.zig b/src/Compilation.zig
index 687525cbf3..01ab281c14 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -173,6 +173,7 @@ verbose_llvm_bc: ?[]const u8,
 verbose_cimport: bool,
 verbose_llvm_cpu_features: bool,
 verbose_link: bool,
+link_depfile: ?[]const u8,
 disable_c_depfile: bool,
 stack_report: bool,
 debug_compiler_runtime_libs: bool,
@@ -1403,6 +1404,7 @@ pub const MiscTask = enum {
     compiler_rt,
     libzigc,
     analyze_mod,
+    link_depfile,
     docs_copy,
     docs_wasm,
 
@@ -1732,6 +1734,7 @@ pub const CreateOptions = struct {
     verbose_generic_instances: bool = false,
     verbose_llvm_ir: ?[]const u8 = null,
     verbose_llvm_bc: ?[]const u8 = null,
+    link_depfile: ?[]const u8 = null,
     verbose_cimport: bool = false,
     verbose_llvm_cpu_features: bool = false,
     debug_compiler_runtime_libs: bool = false,
@@ -2247,6 +2250,7 @@ pub fn create(gpa: Allocator, arena: Allocator, io: Io, diag: *CreateDiagnostic,
             .verbose_generic_instances = options.verbose_generic_instances,
             .verbose_llvm_ir = options.verbose_llvm_ir,
             .verbose_llvm_bc = options.verbose_llvm_bc,
+            .link_depfile = options.link_depfile,
             .verbose_cimport = options.verbose_cimport,
             .verbose_llvm_cpu_features = options.verbose_llvm_cpu_features,
             .verbose_link = options.verbose_link,
@@ -3099,6 +3103,15 @@ pub fn update(comp: *Compilation, main_progress_node: std.Progress.Node) UpdateE
         }
     }
 
+    if (comp.link_depfile) |depfile_path| if (comp.bin_file) |lf| {
+        assert(comp.file_system_inputs != null);
+        comp.createDepFile(depfile_path, lf.emit) catch |err| comp.setMiscFailure(
+            .link_depfile,
+            "unable to write linker dependency file: {t}",
+            .{err},
+        );
+    };
+
     if (anyErrors(comp)) {
         // Skip flushing and keep source files loaded for error reporting.
         return;
@@ -5208,6 +5221,43 @@ pub fn separateCodegenThreadOk(comp: *const Compilation) bool {
     return zcu.backendSupportsFeature(.separate_thread);
 }
 
+fn createDepFile(
+    comp: *Compilation,
+    depfile: []const u8,
+    binfile: Cache.Path,
+) anyerror!void {
+    var buf: [4096]u8 = undefined;
+    var af = try std.fs.cwd().atomicFile(depfile, .{ .write_buffer = &buf });
+    defer af.deinit();
+
+    comp.writeDepFile(binfile, &af.file_writer.interface) catch return af.file_writer.err.?;
+
+    try af.finish();
+}
+
+fn writeDepFile(
+    comp: *Compilation,
+    binfile: Cache.Path,
+    w: *std.Io.Writer,
+) std.Io.Writer.Error!void {
+    const prefixes = comp.cache_parent.prefixes();
+    const fsi = comp.file_system_inputs.?.items;
+
+    try w.print("{f}:", .{binfile});
+
+    {
+        var it = std.mem.splitScalar(u8, fsi, 0);
+        while (it.next()) |input| try w.print(" \\\n {f}{s}", .{ prefixes[input[0] - 1], input[1..] });
+    }
+
+    {
+        var it = std.mem.splitScalar(u8, fsi, 0);
+        while (it.next()) |input| try w.print("\n\n{f}{s}:", .{ prefixes[input[0] - 1], input[1..] });
+    }
+
+    try w.writeByte('\n');
+}
+
 fn workerDocsCopy(comp: *Compilation) void {
     docsCopyFallible(comp) catch |err| return comp.lockAndSetMiscFailure(
         .docs_copy,
diff --git a/src/main.zig b/src/main.zig
index c08e9da449..8112e760df 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -821,6 +821,7 @@ fn buildOutputType(
     var verbose_generic_instances = false;
     var verbose_llvm_ir: ?[]const u8 = null;
     var verbose_llvm_bc: ?[]const u8 = null;
+    var link_depfile: ?[]const u8 = null;
     var verbose_cimport = false;
     var verbose_llvm_cpu_features = false;
     var time_report = false;
@@ -2704,6 +2705,8 @@ fn buildOutputType(
                 {
                     emit_implib = .{ .yes = linker_args_it.nextOrFatal() };
                     emit_implib_arg_provided = true;
+                } else if (mem.eql(u8, arg, "--dependency-file")) {
+                    link_depfile = linker_args_it.nextOrFatal();
                 } else if (mem.eql(u8, arg, "-Brepro") or mem.eql(u8, arg, "/Brepro")) {
                     linker_repro = true;
                 } else if (mem.eql(u8, arg, "-undefined")) {
@@ -3479,6 +3482,7 @@ fn buildOutputType(
         .verbose_generic_instances = verbose_generic_instances,
         .verbose_llvm_ir = verbose_llvm_ir,
         .verbose_llvm_bc = verbose_llvm_bc,
+        .link_depfile = link_depfile,
         .verbose_cimport = verbose_cimport,
         .verbose_llvm_cpu_features = verbose_llvm_cpu_features,
         .time_report = time_report,