Added global-cache argument to build system + removed extra args.

* Field global_cache_root was added to Builder struct along with
mandatory argument for build_runner.zig. Logic for using the custom
global cache was also added.

* The arguments --cache-dir and --global-cache-dir are no longer passed
directly through to build_runner.zig and are instead only passed through the
mandatory cache_root and global_cache_root arguments.

lib/std/build.zig

@@ -61,6 +61,7 @@ pub const Builder = struct {
     installed_files: ArrayList(InstalledFile),
     build_root: []const u8,
     cache_root: []const u8,
+    global_cache_root: []const u8,
     release_mode: ?builtin.Mode,
     is_release: bool,
     override_lib_dir: ?[]const u8,
@@ -126,6 +127,7 @@ pub const Builder = struct {
         zig_exe: []const u8,
         build_root: []const u8,
         cache_root: []const u8,
+        global_cache_root: []const u8,
     ) !*Builder {
         const env_map = try allocator.create(BufMap);
         env_map.* = try process.getEnvMap(allocator);
@@ -135,6 +137,7 @@ pub const Builder = struct {
             .zig_exe = zig_exe,
             .build_root = build_root,
             .cache_root = try fs.path.relative(allocator, build_root, cache_root),
+            .global_cache_root = global_cache_root,
             .verbose = false,
             .verbose_tokenize = false,
             .verbose_ast = false,
@@ -1128,7 +1131,13 @@ test "builder.findProgram compiles" {
     var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
     defer arena.deinit();
 
-    const builder = try Builder.create(&arena.allocator, "zig", "zig-cache", "zig-cache");
+    const builder = try Builder.create(
+        &arena.allocator,
+        "zig",
+        "zig-cache",
+        "zig-cache",
+        "zig-cache",
+    );
     defer builder.destroy();
     _ = builder.findProgram(&[_][]const u8{}, &[_][]const u8{}) catch null;
 }
@@ -2124,6 +2133,9 @@ pub const LibExeObjStep = struct {
         try zig_args.append("--cache-dir");
         try zig_args.append(builder.pathFromRoot(builder.cache_root));
 
+        try zig_args.append("--global-cache-dir");
+        try zig_args.append(builder.pathFromRoot(builder.global_cache_root));
+
         zig_args.append("--name") catch unreachable;
         zig_args.append(self.name) catch unreachable;
 
@@ -2735,6 +2747,7 @@ test "Builder.dupePkg()" {
         "test",
         "test",
         "test",
+        "test",
     );
     defer builder.destroy();
 
@@ -2778,6 +2791,7 @@ test "LibExeObjStep.addBuildOption" {
         "test",
         "test",
         "test",
+        "test",
     );
     defer builder.destroy();
 
@@ -2815,6 +2829,7 @@ test "LibExeObjStep.addPackage" {
         "test",
         "test",
         "test",
+        "test",
     );
     defer builder.destroy();
 

lib/std/special/build_runner.zig

@@ -41,8 +41,18 @@ pub fn main() !void {
         warn("Expected third argument to be cache root directory path\n", .{});
         return error.InvalidArgs;
     };
+    const global_cache_root = nextArg(args, &arg_idx) orelse {
+        warn("Expected third argument to be global cache root directory path\n", .{});
+        return error.InvalidArgs;
+    };
 
-    const builder = try Builder.create(allocator, zig_exe, build_root, cache_root);
+    const builder = try Builder.create(
+        allocator,
+        zig_exe,
+        build_root,
+        cache_root,
+        global_cache_root,
+    );
     defer builder.destroy();
 
     var targets = ArrayList([]const u8).init(allocator);

src/main.zig

@@ -2228,6 +2228,9 @@ pub fn cmdBuild(gpa: *Allocator, arena: *Allocator, args: []const []const u8) !v
         const argv_index_cache_dir = child_argv.items.len;
         _ = try child_argv.addOne();
 
+        const argv_index_global_cache_dir = child_argv.items.len;
+        _ = try child_argv.addOne();
+
         {
             var i: usize = 0;
             while (i < args.len) : (i += 1) {
@@ -2248,13 +2251,11 @@ pub fn cmdBuild(gpa: *Allocator, arena: *Allocator, args: []const []const u8) !v
                         if (i + 1 >= args.len) fatal("expected argument after '{}'", .{arg});
                         i += 1;
                         override_local_cache_dir = args[i];
-                        try child_argv.appendSlice(&[_][]const u8{ arg, args[i] });
                         continue;
                     } else if (mem.eql(u8, arg, "--global-cache-dir")) {
                         if (i + 1 >= args.len) fatal("expected argument after '{}'", .{arg});
                         i += 1;
                         override_global_cache_dir = args[i];
-                        try child_argv.appendSlice(&[_][]const u8{ arg, args[i] });
                         continue;
                     }
                 }
@@ -2339,6 +2340,8 @@ pub fn cmdBuild(gpa: *Allocator, arena: *Allocator, args: []const []const u8) !v
         };
         defer global_cache_directory.handle.close();
 
+        child_argv.items[argv_index_global_cache_dir] = global_cache_directory.path orelse cwd_path;
+
         var local_cache_directory: Compilation.Directory = l: {
             if (override_local_cache_dir) |local_cache_dir_path| {
                 break :l .{