func merge()

in unix/internal/mkmerge/mkmerge.go [424:492]
55 lines of code
13 McCabe index (conditional complexity)

func merge(mergedFile string, archFiles ...string) error {
	// extract and validate the GOOS part of the merged filename
	goos, ok := getValidGOOS(mergedFile)
	if !ok {
		return fmt.Errorf("invalid GOOS in merged file name %s", mergedFile)
	}

	// Read architecture files
	var inSrc []srcFile
	for _, file := range archFiles {
		src, err := ioutil.ReadFile(file)
		if err != nil {
			return fmt.Errorf("cannot read archfile %s: %w", file, err)
		}

		inSrc = append(inSrc, srcFile{file, src})
	}

	// 1. Construct the set of top-level declarations common for all files
	commonSet, err := getCommonSet(inSrc)
	if err != nil {
		return err
	}
	if commonSet.isEmpty() {
		// No common code => do not modify any files
		return nil
	}

	// 2. Write the merged file
	mergedSrc, err := filter(inSrc[0].src, commonSet.keepCommon)
	if err != nil {
		return err
	}

	f, err := os.Create(mergedFile)
	if err != nil {
		return err
	}

	buf := bufio.NewWriter(f)
	fmt.Fprintln(buf, "// Code generated by mkmerge; DO NOT EDIT.")
	fmt.Fprintln(buf)
	fmt.Fprintf(buf, "//go:build %s\n", goos)
	fmt.Fprintf(buf, "// +build %s\n", goos)
	fmt.Fprintln(buf)
	buf.Write(mergedSrc)

	err = buf.Flush()
	if err != nil {
		return err
	}
	err = f.Close()
	if err != nil {
		return err
	}

	// 3. Remove duplicate declarations from the architecture files
	for _, inFile := range inSrc {
		src, err := filter(inFile.src, commonSet.keepArchSpecific)
		if err != nil {
			return err
		}
		err = ioutil.WriteFile(inFile.name, src, 0644)
		if err != nil {
			return err
		}
	}
	return nil
}