CLI: introduce global -I args for C include paths

This isn't technically needed since per-module -I args can suffice, but
this can produce very long CLI invocations when several --mod args are
combined with --search-prefix args since the -I args have to be repeated
for each module.

This is a partial revert of ecbe8bbf2df2ed4d473efbc32e0b6d7091fba76f.

2 files changed, 14 insertions, 3 deletions

diff --git a/src/Compilation.zig b/src/Compilation.zig
index 11b3328e0e..98f4012a26 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -165,6 +165,7 @@ last_update_was_cache_hit: bool = false,
 
 c_source_files: []const CSourceFile,
 rc_source_files: []const RcSourceFile,
+global_cc_argv: []const []const u8,
 cache_parent: *Cache,
 /// Path to own executable for invoking `zig clang`.
 self_exe_path: ?[]const u8,
@@ -1120,6 +1121,7 @@ pub const CreateOptions = struct {
     /// (Windows) PDB output path
     pdb_out_path: ?[]const u8 = null,
     error_limit: ?Compilation.Module.ErrorInt = null,
+    global_cc_argv: []const []const u8 = &.{},
 
     pub const Entry = link.File.OpenOptions.Entry;
 };
@@ -1515,6 +1517,7 @@ pub fn create(gpa: Allocator, arena: Allocator, options: CreateOptions) !*Compil
             .wasi_emulated_libs = options.wasi_emulated_libs,
             .force_undefined_symbols = options.force_undefined_symbols,
             .link_eh_frame_hdr = link_eh_frame_hdr,
+            .global_cc_argv = options.global_cc_argv,
         };
 
         // Prevent some footguns by making the "any" fields of config reflect
@@ -2527,6 +2530,8 @@ fn addNonIncrementalStuffToCacheManifest(
     cache_helpers.addOptionalEmitLoc(&man.hash, comp.emit_llvm_ir);
     cache_helpers.addOptionalEmitLoc(&man.hash, comp.emit_llvm_bc);
 
+    man.hash.addListOfBytes(comp.global_cc_argv);
+
     const opts = comp.cache_use.whole.lf_open_opts;
 
     try man.addOptionalFile(opts.linker_script);
@@ -3941,6 +3946,7 @@ pub fn obtainCObjectCacheManifest(
     // that apply both to @cImport and compiling C objects. No linking stuff here!
     // Also nothing that applies only to compiling .zig code.
     cache_helpers.addModule(&man.hash, owner_mod);
+    man.hash.addListOfBytes(comp.global_cc_argv);
     man.hash.add(comp.config.link_libcpp);
 
     // When libc_installation is null it means that Zig generated this dir list
@@ -5411,6 +5417,7 @@ pub fn addCCArgs(
         }
     }
 
+    try argv.appendSlice(comp.global_cc_argv);
     try argv.appendSlice(mod.cc_argv);
 }
 
diff --git a/src/main.zig b/src/main.zig
index 091e4b2668..4442234bd2 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -3244,6 +3244,10 @@ fn buildOutputType(
         .pdb_out_path = pdb_out_path,
         .error_limit = error_limit,
         .native_system_include_paths = create_module.native_system_include_paths,
+        // Any leftover C compilation args (such as -I) apply globally rather
+        // than to any particular module. This feature can greatly reduce CLI
+        // noise when --search-prefix and --mod are combined.
+        .global_cc_argv = try cc_argv.toOwnedSlice(arena),
     }) catch |err| switch (err) {
         error.LibCUnavailable => {
             const triple_name = try target.zigTriple(arena);
@@ -3421,9 +3425,9 @@ const CreateModule = struct {
     c_source_files: std.ArrayListUnmanaged(Compilation.CSourceFile),
     rc_source_files: std.ArrayListUnmanaged(Compilation.RcSourceFile),
 
-    // e.g. -m3dnow or -mno-outline-atomics. They correspond to std.Target llvm cpu feature names.
-    // This array is populated by zig cc frontend and then has to be converted to zig-style
-    // CPU features.
+    /// e.g. -m3dnow or -mno-outline-atomics. They correspond to std.Target llvm cpu feature names.
+    /// This array is populated by zig cc frontend and then has to be converted to zig-style
+    /// CPU features.
     llvm_m_args: std.ArrayListUnmanaged([]const u8),
     sysroot: ?[]const u8,
     lib_dirs: std.ArrayListUnmanaged([]const u8),