CommandLine.template accepts NAME+=value as the program name #9862

CommandLine.template rejects a variable assignment in the program position, but only the NAME=value form. The append form NAME+=value, which bash and zsh (and macOS sh) also read as an assignment, is accepted and becomes the program name:

import { CommandLine } from "effect/process"

CommandLine.template`FOO=bar make`
// Failure: UnsupportedSyntax "A variable assignment needs a shell"

CommandLine.template`FOO+=bar make`
// Success: ["FOO+=bar", "make"]

In bash or zsh, FOO+=bar make runs make with FOO set. ChildProcess.make splits its template with CommandLine.template, so ChildProcess.make`FOO+=bar make` tries to run a program named FOO+=bar instead.

On v4/next-minor (unreleased, added in #9752). I have a small fix with a test and will open a PR.