CLI tools don't preserve v:progname, v:progpath

Describe the bug
Vim exposes the name of the binary that was executed in the v:progname variable. Unfortunately, invoking the various vim CLI tools installed by MacVim always reports v:progname as being Vim. This is because they're all symlinks of the embedded mvim script, which ultimately invokes

exec "$binary" $opts …

In particular, it's not providing the -a flag, so the binary is always invoked with the executable name of Vim.

The same issue also affects v:progpath (for obvious reasons), wherein it always points to the absolute path to the MacVim.app/Contents/MacOS/Vim binary.

This is an issue because v:progname and v:progpath are potentially useful to use in my vimrc to customize based on what binary I used to invoke it.

Replacing this with exec -a "$0" "$binary" … should solve the problem.

On a related note, launching MacVim from the Finder also sets v:progname to Vim. I can't decide if this matters.

To Reproduce
Detailed steps to reproduce the behavior:

1. Run ex
2. Type echo v:progname or echo v:progpath

Expected behavior
It should print "ex" as the progname and either "ex" or the absolute path to ex as the progpath.

Observed behavior
It always prints Vim as the progname and the absolute path to MacVim.app/Contents/MacOS/Vim as the progpath.

Environment (please complete the following information):

• Vim version 8.2.1719
• OS: macOS 11.2.3 (20D91)
• Terminal: Apple Terminal.app or GUI

埋め込まれている mvim スクリプトから始め、シンボリックリンクされた CLI ツールに対して Vim バイナリをどのように呼び出しているかを調べます。ex と echo v:progname および v:progpath を使って再現し、その後、他の起動動作を変更せずに呼び出しがツール名またはパスを保持することを確認します。