From 041212a41cfaf029dc3eb9740467b721c76f406c Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Thu, 4 Mar 2021 18:14:00 -0700
Subject: [PATCH] zig cc: fix handling of -MM flag

Clang docs say:
> Like -MMD, but also implies -E and writes to stdout by default.

Previously, Zig handled this option by forwarding it directly to Clang,
and disabling depfiles. However this did not adhere to Clang's documented
behavior of these flags.

Now, in addition to being forwarded directly to Clang, `-MM` also
sets c_out_mode = .preprocessor, just like `-E`.

Another issue I noticed is that Zig did not recognize the aliases for
-MG, -MM, or -MMD. The aliases are now recognized.
---
 src/clang_options_data.zig     | 10 +++++-----
 src/main.zig                   |  7 +++++++
 tools/update_clang_options.zig | 18 +++++++++++++++++-
 3 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/src/clang_options_data.zig b/src/clang_options_data.zig
index 0293a5327e..b1cb6c258c 100644
--- a/src/clang_options_data.zig
+++ b/src/clang_options_data.zig
@@ -46,7 +46,7 @@ flagpd1("M"),
 .{
     .name = "MM",
     .syntax = .flag,
-    .zig_equivalent = .dep_file,
+    .zig_equivalent = .dep_file_mm,
     .pd1 = true,
     .pd2 = false,
     .psl = false,
@@ -1878,7 +1878,7 @@ flagpsl("MT"),
 .{
     .name = "print-missing-file-dependencies",
     .syntax = .flag,
-    .zig_equivalent = .other,
+    .zig_equivalent = .dep_file,
     .pd1 = false,
     .pd2 = true,
     .psl = false,
@@ -1998,7 +1998,7 @@ flagpsl("MT"),
 .{
     .name = "user-dependencies",
     .syntax = .flag,
-    .zig_equivalent = .other,
+    .zig_equivalent = .dep_file_mm,
     .pd1 = false,
     .pd2 = true,
     .psl = false,
@@ -2022,7 +2022,7 @@ flagpsl("MT"),
 .{
     .name = "write-dependencies",
     .syntax = .flag,
-    .zig_equivalent = .other,
+    .zig_equivalent = .dep_file,
     .pd1 = false,
     .pd2 = true,
     .psl = false,
@@ -2030,7 +2030,7 @@ flagpsl("MT"),
 .{
     .name = "write-user-dependencies",
     .syntax = .flag,
-    .zig_equivalent = .other,
+    .zig_equivalent = .dep_file,
     .pd1 = false,
     .pd2 = true,
     .psl = false,
diff --git a/src/main.zig b/src/main.zig
index 3b71379cb0..011b9edf76 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -1192,6 +1192,12 @@ fn buildOutputType(
                         disable_c_depfile = true;
                         try clang_argv.appendSlice(it.other_args);
                     },
+                    .dep_file_mm => { // -MM
+                        // "Like -MMD, but also implies -E and writes to stdout by default"
+                        c_out_mode = .preprocessor;
+                        disable_c_depfile = true;
+                        try clang_argv.appendSlice(it.other_args);
+                    },
                     .framework_dir => try framework_dirs.append(it.only_arg),
                     .framework => try frameworks.append(it.only_arg),
                     .nostdlibinc => want_native_include_dirs = false,
@@ -3055,6 +3061,7 @@ pub const ClangArgIterator = struct {
         lib_dir,
         mcpu,
         dep_file,
+        dep_file_mm,
         framework_dir,
         framework,
         nostdlibinc,
diff --git a/tools/update_clang_options.zig b/tools/update_clang_options.zig
index 1cb134a731..f0dfe1639d 100644
--- a/tools/update_clang_options.zig
+++ b/tools/update_clang_options.zig
@@ -268,6 +268,10 @@ const known_options = [_]KnownOpt{
         .name = "MD",
         .ident = "dep_file",
     },
+    .{
+        .name = "write-dependencies",
+        .ident = "dep_file",
+    },
     .{
         .name = "MV",
         .ident = "dep_file",
@@ -284,18 +288,30 @@ const known_options = [_]KnownOpt{
         .name = "MG",
         .ident = "dep_file",
     },
+    .{
+        .name = "print-missing-file-dependencies",
+        .ident = "dep_file",
+    },
     .{
         .name = "MJ",
         .ident = "dep_file",
     },
     .{
         .name = "MM",
-        .ident = "dep_file",
+        .ident = "dep_file_mm",
+    },
+    .{
+        .name = "user-dependencies",
+        .ident = "dep_file_mm",
     },
     .{
         .name = "MMD",
         .ident = "dep_file",
     },
+    .{
+        .name = "write-user-dependencies",
+        .ident = "dep_file",
+    },
     .{
         .name = "MP",
         .ident = "dep_file",