WhitespacePreservation.md

Whitespace Preservation

Someone requested that code blocks preserve their indentation level when expanded. It seems like a reasonable request, that should make it possible to do things like use Python.

To do that, we'll have to group the whitespace token in the Replace Regex so that we know the indentation level to preserve.

replaceRe = regexp.MustCompile(`^([\s]*)<<<(.+)>>>[\s]*$`)

Then update the reference to it when looking up the replacement, since the index will have changed. We'll also want to pass the whitespace token we just found to Replace() to use as a prefix (in addition to the current prefix.)

(We probably should have used a named grouping, but for now we'll just change the index to keep our changes simple.)

bname := BlockName(matches[2])
if val, ok := blocks[bname]; ok {
	ret += val.Replace(prefix + matches[1])
} else {
	fmt.Fprintf(os.Stderr, "Warning: Block named %s referenced but not defined.\n", bname)
	ret += CodeBlock(line)
}

We'll have to update our function signature too.

// Replace expands all macros in a CodeBlock and returns a CodeBlock with no
// references to macros.
func (c CodeBlock) Replace(prefix string) (ret CodeBlock) {
	<<<Replace codeblock implementation>>>
}

and make sure we pass the empty string as the starting prefix when outputting a new file.

for filename, codeblock := range files {
	f, err := os.Create(string(filename))
	if err != nil {
		fmt.Fprintf(os.Stderr, "%v\n", err)
		continue
	}
	fmt.Fprintf(f, "%s", codeblock.Replace(""))
	// We don't defer this so that it'll get closed before the loop finishes.
	f.Close()

}

Then all that's left is, when replacing lines, we'll have to include the prefix that we just passed, so that the lines get indented. But only if the line isn't empty.

matches := replaceRe.FindStringSubmatch(line)
if matches == nil {
	if line != "\n" {
		ret += CodeBlock(prefix)
	}
	ret += CodeBlock(line)
	continue
}
<<<Lookup replacement and add to ret>>>

And now our generated code looks prettier without needing an autoformatter like go fmt.