Blocking echo messages on startup result in blank screen

首先使用 mvim --clean 重现该命令，并将空白启动屏幕与 plain vim 的消息显示进行比较。跟踪 MacVim 如何处理启动 echo 消息和 diff-editor 启动，然后验证警告会在编辑器可用之前出现，且不需要额外按一次 Enter。

Steps to reproduce

With the latest prerelease, I run the following command (from a draft default diff tool config similar to https://github.com/jj-vcs/jj/pull/6205, sorry for extraneous quotes):

Update: I changed this line to remove irrelevant backticks. They mess up the result in bash or zsh; I didn't notice because I use fish.

"gvim" "-f" "-d" "-u" "/dev/null" mkdocs-offline.yml mkdocs.yml "-c" "echohl WarningMsg" "-c" "echomsg \"Warning: using plain vimdiff as a diff editor is not recommended. See https://github.com/jj-vcs/jj/wiki/Vim for alternatives.\"" "-c" "echohl None"

(It doesn't matter which two files you'd be comparing, or if they even exist)

This results in a confusing blank screen instead of the expected message:

After pressing Enter, everything works.

Expected behaviour

In plain vim, I get:

"mkdocs-offline.yml" 19 lines, 724 bytes
"mkdocs.yml" 154 lines, 4992 bytes
Warning: using plain `vimdiff` as a diff editor is not recommended. See https://github.com/jj-vcs/jj/wiki/Vim for alternatives.
Press ENTER or type command to continue

Then, vim loads after I press ENTER.

Version of Vim and architecture

1-1251

Environment

VIM - Vi IMproved 9.1 (2024 Jan 02, compiled Mar 28 2025 09:26:05)
macOS version - arm64
Included patches: 1-1251
Compiled by GitHub Actions

How MacVim was installed

Downloaded from GitHub

Logs and stack traces

Vim configuration where issue is reproducable

No response

Issue has been tested with given configuration

• by running MacVim.app from GUI macOS interface
• by running vim/gvim/etc installed by MacVim
• by running other versions of vim (e.g. /usr/bin/vim)

Issue has been tested with no configuration

• by running mvim --clean (or gvim, supplied by MacVim distribution)
• by running vim --clean (in terminal, supplied by MacVim distribution)
• by running vim --clean (in terminal, other suppliers, e.g. /usr/bin/vim)

Other conditions

• The both Homebrew packages "vim" and "macvim" are installed