From 308ba80597864ab12b77cff1ce28f001ad551fdf Mon Sep 17 00:00:00 2001
From: zhylmzr <zhylmzr@gmail.com>
Date: Tue, 23 Jul 2024 01:53:51 +0800
Subject: [PATCH] fix(cc): make link and preprocessor logic to be more
 consistent with clang's behavior.

1. `zig cc main.c -o /dev/null` shouldn't emit a.out
2. `zig cc -E main.c` and `zig cc -E main -o -` should output to stdout
---
 src/main.zig | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/main.zig b/src/main.zig
index 1177a0baab..34d610bdd1 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -2718,7 +2718,9 @@ fn buildOutputType(
             switch (c_out_mode orelse .link) {
                 .link => {
                     create_module.opts.output_mode = if (is_shared_lib) .Lib else .Exe;
-                    emit_bin = if (out_path) |p| .{ .yes = p } else EmitBin.yes_a_out;
+                    if (emit_bin != .no) {
+                        emit_bin = if (out_path) |p| .{ .yes = p } else EmitBin.yes_a_out;
+                    }
                     if (emit_llvm) {
                         fatal("-emit-llvm cannot be used when linking", .{});
                     }
@@ -2768,10 +2770,13 @@ fn buildOutputType(
                         emit_bin = if (out_path) |p| .{ .yes = p } else .yes_default_path;
                         clang_preprocessor_mode = .pch;
                     } else {
-                        if (out_path) |p| {
-                            emit_bin = .{ .yes = p };
+                        // If the output path is "-" (stdout), then we need to emit the preprocessed output to stdout
+                        // like "clang -E main.c -o -" does.
+                        if (out_path != null and !mem.eql(u8, out_path.?, "-")) {
+                            emit_bin = .{ .yes = out_path.? };
                             clang_preprocessor_mode = .yes;
                         } else {
+                            emit_bin = .no;
                             clang_preprocessor_mode = .stdout;
                         }
                     }