makefile: Sanitize date output from git log

Problem

Running make on a fresh checkout of this repository will fail if your global Git configuration has signature verification enabled for git log. It prints a confusing error message like the following from my PC:

$ make
sed 's#^RUNTIME=.*$#RUNTIME='"'/usr/local/share/nvimpager/runtime'"'#;s#version=.*$#version=v0.9-7-g458ca0d#' < nvimpager > nvimpager.configured
chmod +x nvimpager.configured
echo "---" > metadata.yaml
echo "footer: Version v0.9-7-g458ca0d" >> metadata.yaml
echo "date: gpg: Signature made Sat 10 Apr 2021 06:15:09 AM CDT gpg:                using RSA key 4AEE18F83AFDEB23 gpg: Good signature from "GitHub (web-flow commit signing) <noreply@github.com>" [full] 2021-04-10" >> metadata.yaml
/bin/sh: 1: Syntax error: "(" unexpected
make: *** [makefile:31: metadata.yaml] Error 2

The problem seems to be either the embedded quotes or embedded parentheses in substring "GitHub (web-flow commit signing) <noreply@github.com>", and the unescaped string at makefile:31:

    echo "date: $(DATE)" >> $@

Change

This change simply suppresses signature verification with git log --no-show-signature when building the $(DATE) string.

Verification

Now make runs to completion:

$ make
sed 's#^RUNTIME=.*$#RUNTIME='"'/usr/local/share/nvimpager/runtime'"'#;s#version=.*$#version=v0.9-7-g458ca0d#' < nvimpager > nvimpager.configured
chmod +x nvimpager.configured
echo "---" > metadata.yaml
echo "footer: Version v0.9-7-g458ca0d" >> metadata.yaml
echo "date: 2021-04-10" >> metadata.yaml
echo "..." >> metadata.yaml
pandoc --standalone --to man --output nvimpager.1 nvimpager.md metadata.yaml
mkdir -p /usr/local/bin /usr/local/share/nvimpager/runtime/lua \
  /usr/local/share/man/man1 \
  /usr/local/share/zsh/site-functions
install nvimpager.configured /usr/local/bin/nvimpager
install lua/nvimpager.lua /usr/local/share/nvimpager/runtime/lua
install nvimpager.1 /usr/local/share/man/man1
install _nvimpager /usr/local/share/zsh/site-functions

With metadata.yaml containing the following:

$ cat metadata.yaml
---
footer: Version v0.9-7-g458ca0d
date: 2021-04-10
...

Notes

It may be better (safer) to escape all of the strings constructed via $(shell ...) function, as there are probably other configurations that can produce similar errors.

lucc / nvimpager