Dead code elimination partially disabled

[seanamos]

urfave/cli directly uses text/template, and unfortunately this partially disables dead code elimination. However, "partial" in this context can result in significantly larger binaries depending on how many other dependencies you have. Full DCE can result in significant binary size reductions (50%+-).

Cobra recently added a fix/workaround for a similar issue:
spf13/cobra#1956

I appreciate there may not be a non-breaking way to solve this in v3.

[seanamos]

See also the relevant discussion here: golang/go#72895

[seanamos]

I did a quick experiment (really hacked together) to demonstrate how significant this is.

In the empty hello world example, the binary size dropped to 1.3mb from 2.0mb

Usin my local fork in a more real world project with a binary size of 33mb, the size dropped to 8mb.

The approach I used? Swap out the usage of text/template for Datadog's fork: https://github.com/DataDog/datadog-agent/tree/main/pkg/template/text

The Datadog fork is a drop in replacement for stdlib, with one major difference, it does not use reflect.MethodByName to avoid disabling DCE. Datadog have run into the exact same problem: https://www.datadoghq.com/blog/engineering/agent-go-binaries/

This means you cannot call methods from within templates, FullName(), VisibleFlags() etc. .
I copied the necessary data from the Command into another struct, with no methods, and pass that as the template data.

	tdata = templateCommand{
		ArgsUsage:              cmd.ArgsUsage,
		Authors:                cmd.Authors,
		Category:               cmd.Category,
		Copyright:              cmd.Copyright,
		Description:            cmd.Description,
		Flags:                  cmd.Flags,
		FullName:               cmd.FullName(),
		HideVersion:            cmd.HideVersion,
		Name:                   cmd.Name,
		Names:                  cmd.Names(),
		Usage:                  cmd.Usage,
		UsageText:              cmd.UsageText,
		Version:                cmd.Version,
		VisibleCategories:      tvcats,
		VisibleCommands:        tvcmds,
		VisibleFlags:           cmd.VisibleFlags(),
		VisibleFlagCategories:  tvflagcats,
		VisiblePersistentFlags: cmd.VisiblePersistentFlags(),
		Arguments:              targs,

	tracef("executing template")
	handleTemplateError(t.Execute(w, tdata))

There are some other changes, but that was the general idea.

[abitrolly]

It looks like this should be in Go stdlib.

[abitrolly]

Could this help with eliminating completions code that is not used? #2291