fix build logic due to state mutations and break the API accordingly

 * remove setName, setFilter, and setTestRunner. Please set these
   options directly when creating the CompileStep.
 * removed unused field
 * remove computeOutFileNames and inline the logic, making clear the
   goal of avoiding state mutations after the build step is created.

2 files changed, 41 insertions, 58 deletions

diff --git a/lib/std/Build.zig b/lib/std/Build.zig
index 5b974bb816..7faa7780b2 100644
--- a/lib/std/Build.zig
+++ b/lib/std/Build.zig
@@ -539,6 +539,8 @@ pub const TestOptions = struct {
     optimize: std.builtin.Mode = .Debug,
     version: ?std.builtin.Version = null,
     max_rss: usize = 0,
+    filter: ?[]const u8 = null,
+    test_runner: ?[]const u8 = null,
 };
 
 pub fn addTest(b: *Build, options: TestOptions) *CompileStep {
@@ -549,6 +551,8 @@ pub fn addTest(b: *Build, options: TestOptions) *CompileStep {
         .target = options.target,
         .optimize = options.optimize,
         .max_rss = options.max_rss,
+        .filter = options.filter,
+        .test_runner = options.test_runner,
     });
 }
 
diff --git a/lib/std/Build/CompileStep.zig b/lib/std/Build/CompileStep.zig
index ceacc87dca..5c3b166282 100644
--- a/lib/std/Build/CompileStep.zig
+++ b/lib/std/Build/CompileStep.zig
@@ -97,8 +97,6 @@ out_lib_filename: []const u8,
 out_pdb_filename: []const u8,
 modules: std.StringArrayHashMap(*Module),
 
-object_src: []const u8,
-
 link_objects: ArrayList(LinkObject),
 include_dirs: ArrayList(IncludeDir),
 c_macros: ArrayList([]const u8),
@@ -287,6 +285,8 @@ pub const Options = struct {
     linkage: ?Linkage = null,
     version: ?std.builtin.Version = null,
     max_rss: usize = 0,
+    filter: ?[]const u8 = null,
+    test_runner: ?[]const u8 = null,
 };
 
 pub const Kind = enum {
@@ -339,6 +339,23 @@ pub fn create(owner: *std.Build, options: Options) *CompileStep {
         options.target.zigTriple(owner.allocator) catch @panic("OOM"),
     });
 
+    const target_info = NativeTargetInfo.detect(options.target) catch @panic("unhandled error");
+
+    const out_filename = std.zig.binNameAlloc(owner.allocator, .{
+        .root_name = name,
+        .target = target_info.target,
+        .output_mode = switch (options.kind) {
+            .lib => .Lib,
+            .obj => .Obj,
+            .exe, .@"test" => .Exe,
+        },
+        .link_mode = if (options.linkage) |some| @as(std.builtin.LinkMode, switch (some) {
+            .dynamic => .Dynamic,
+            .static => .Static,
+        }) else null,
+        .version = options.version,
+    }) catch @panic("OOM");
+
     const self = owner.allocator.create(CompileStep) catch @panic("OOM");
     self.* = CompileStep{
         .strip = null,
@@ -360,7 +377,7 @@ pub fn create(owner: *std.Build, options: Options) *CompileStep {
             .max_rss = options.max_rss,
         }),
         .version = options.version,
-        .out_filename = undefined,
+        .out_filename = out_filename,
         .out_h_filename = owner.fmt("{s}.h", .{name}),
         .out_lib_filename = undefined,
         .out_pdb_filename = owner.fmt("{s}.pdb", .{name}),
@@ -374,13 +391,12 @@ pub fn create(owner: *std.Build, options: Options) *CompileStep {
         .rpaths = ArrayList(FileSource).init(owner.allocator),
         .framework_dirs = ArrayList(FileSource).init(owner.allocator),
         .installed_headers = ArrayList(*Step).init(owner.allocator),
-        .object_src = undefined,
         .c_std = std.Build.CStd.C99,
         .zig_lib_dir = null,
         .main_pkg_path = null,
         .exec_cmd_args = null,
-        .filter = null,
-        .test_runner = null,
+        .filter = options.filter,
+        .test_runner = options.test_runner,
         .disable_stack_probing = false,
         .disable_sanitize_c = false,
         .sanitize_thread = false,
@@ -395,60 +411,41 @@ pub fn create(owner: *std.Build, options: Options) *CompileStep {
         .output_pdb_path_source = GeneratedFile{ .step = &self.step },
         .output_dirname_source = GeneratedFile{ .step = &self.step },
 
-        .target_info = NativeTargetInfo.detect(self.target) catch @panic("unhandled error"),
+        .target_info = target_info,
     };
-    self.computeOutFileNames();
-    if (root_src) |rs| rs.addStepDependencies(&self.step);
-    return self;
-}
-
-fn computeOutFileNames(self: *CompileStep) void {
-    const b = self.step.owner;
-    const target = self.target_info.target;
-
-    self.out_filename = std.zig.binNameAlloc(b.allocator, .{
-        .root_name = self.name,
-        .target = target,
-        .output_mode = switch (self.kind) {
-            .lib => .Lib,
-            .obj => .Obj,
-            .exe, .@"test" => .Exe,
-        },
-        .link_mode = if (self.linkage) |some| @as(std.builtin.LinkMode, switch (some) {
-            .dynamic => .Dynamic,
-            .static => .Static,
-        }) else null,
-        .version = self.version,
-    }) catch @panic("OOM");
 
     if (self.kind == .lib) {
         if (self.linkage != null and self.linkage.? == .static) {
             self.out_lib_filename = self.out_filename;
         } else if (self.version) |version| {
-            if (target.isDarwin()) {
-                self.major_only_filename = b.fmt("lib{s}.{d}.dylib", .{
+            if (target_info.target.isDarwin()) {
+                self.major_only_filename = owner.fmt("lib{s}.{d}.dylib", .{
                     self.name,
                     version.major,
                 });
-                self.name_only_filename = b.fmt("lib{s}.dylib", .{self.name});
+                self.name_only_filename = owner.fmt("lib{s}.dylib", .{self.name});
                 self.out_lib_filename = self.out_filename;
-            } else if (target.os.tag == .windows) {
-                self.out_lib_filename = b.fmt("{s}.lib", .{self.name});
+            } else if (target_info.target.os.tag == .windows) {
+                self.out_lib_filename = owner.fmt("{s}.lib", .{self.name});
             } else {
-                self.major_only_filename = b.fmt("lib{s}.so.{d}", .{ self.name, version.major });
-                self.name_only_filename = b.fmt("lib{s}.so", .{self.name});
+                self.major_only_filename = owner.fmt("lib{s}.so.{d}", .{ self.name, version.major });
+                self.name_only_filename = owner.fmt("lib{s}.so", .{self.name});
                 self.out_lib_filename = self.out_filename;
             }
         } else {
-            if (target.isDarwin()) {
+            if (target_info.target.isDarwin()) {
                 self.out_lib_filename = self.out_filename;
-            } else if (target.os.tag == .windows) {
-                self.out_lib_filename = b.fmt("{s}.lib", .{self.name});
+            } else if (target_info.target.os.tag == .windows) {
+                self.out_lib_filename = owner.fmt("{s}.lib", .{self.name});
             } else {
                 self.out_lib_filename = self.out_filename;
             }
         }
     }
+
+    if (root_src) |rs| rs.addStepDependencies(&self.step);
+
+    return self;
 }
 
 pub fn installHeader(cs: *CompileStep, src_path: []const u8, dest_rel_path: []const u8) void {
@@ -841,24 +838,6 @@ fn linkSystemLibraryInner(self: *CompileStep, name: []const u8, opts: struct {
     }) catch @panic("OOM");
 }
 
-pub fn setName(self: *CompileStep, text: []const u8) void {
-    const b = self.step.owner;
-    assert(self.kind == .@"test");
-    self.name = b.dupe(text);
-}
-
-pub fn setFilter(self: *CompileStep, text: ?[]const u8) void {
-    const b = self.step.owner;
-    assert(self.kind == .@"test");
-    self.filter = if (text) |t| b.dupe(t) else null;
-}
-
-pub fn setTestRunner(self: *CompileStep, path: ?[]const u8) void {
-    const b = self.step.owner;
-    assert(self.kind == .@"test");
-    self.test_runner = if (path) |p| b.dupePath(p) else null;
-}
-
 /// Handy when you have many C/C++ source files and want them all to have the same flags.
 pub fn addCSourceFiles(self: *CompileStep, files: []const []const u8, flags: []const []const u8) void {
     const b = self.step.owner;