tags := map[string]bool{}
			shouldBuild, binaryOnly, err := ctx.shouldBuild([]byte(tt.content), tags)
			if shouldBuild != tt.shouldBuild || binaryOnly != tt.binaryOnly || !reflect.DeepEqual(tags, tt.tags) || err != tt.err {
				t.Errorf("mismatch:\n"+
					"have shouldBuild=%v, binaryOnly=%v, tags=%v, err=%v\n"+
					"want shouldBuild=%v, binaryOnly=%v, tags=%v, err=%v",
					shouldBuild, binaryOnly, tags, err,

	}

	// If //go:build line is present, it controls.
	// Otherwise fall back to +build processing.
	var shouldBuild bool
	switch {
	case goBuild != nil:
		x, err := constraint.Parse(string(goBuild))
		if err != nil {
			return false
		}
		shouldBuild = eval(x, tags, true)

	default:
		shouldBuild = true
		p := content
		for len(p) > 0 {
			line := p
			if i := bytes.IndexByte(line, '\n'); i >= 0 {

			}
		}

		var shouldBuild = true
		if !ctxt.goodOSArchFile(name, allTags) && !ctxt.UseAllFiles {
			shouldBuild = false
		} else if goBuildConstraint := tf.goBuildConstraint(); goBuildConstraint != "" {
			x, err := constraint.Parse(goBuildConstraint)
			if err != nil {
				return p, fmt.Errorf("%s: parsing //go:build line: %v", name, err)
			}
			shouldBuild = ctxt.eval(x, allTags)

		f, err := fsys.Open(filepath.Join(dir, info.Name()))
		if err != nil {
			base.Fatal(err)
		}
		defer f.Close()

		content, err := imports.ReadImports(f, false, nil)
		if err == nil && !imports.ShouldBuild(content, imports.AnyTags()) {
			// The file is explicitly tagged "ignore", so it can't affect the build.
			// Leave it out.
			return false
		}
		return true
	}