CI: Enable the verbose mode in the mkmf.rb.

Enable the verbose option in mkmf.rb to print the compiling commands in the
process of the `rake compile`. Because it's helpful to see what compiler
warnings are checked.

The script only runs in Linux and macOS. Not Windows. Because the sh script
doesn't work in Windows. For the syntax, see the reference.[1]

Right now there is a way to configure Ruby with `--enable-mkmf-verbose` in this
purpose. But there is no formal way to enable the verbose mode in runtime of
Ruby. My intention is that this commit is a workaround for this purpose.

[1] https://docs.github.com/en/actions/learn-github-actions/variables
  * Default environment variables - RUNNER_OS
  * Detecting the operating system

.github/workflows/test.yml

@@ -42,6 +42,11 @@ jobs:
       - name: depends
         run:  bundle install
 
+      # Enable the verbose option in mkmf.rb to print the compiling commands.
+      - name: enable mkmf verbose
+        run:  tool/enable-mkmf-verbose
+        if: runner.os == 'Linux' || runner.os == 'macOS'
+
       - name: compile
         run:  rake compile -- --enable-debug
 
@@ -129,6 +134,10 @@ jobs:
       - name: depends
         run:  bundle install
 
+      - name: enable mkmf verbose
+        run:  tool/enable-mkmf-verbose
+        if: runner.os == 'Linux' || runner.os == 'macOS'
+
       - name: compile
         run:  rake compile -- --enable-debug --with-openssl-dir=$HOME/.openssl/${{ matrix.openssl }}
 

tool/enable-mkmf-verbose

@@ -0,0 +1,24 @@
+#!/bin/sh
+
+set -eux
+
+gem_home="$(gem environment home)"
+mkmf_rb_path="$(find "${gem_home}"/../.. -name mkmf.rb)"
+
+# Backup the original file.
+cp -p "${mkmf_rb_path}" "${mkmf_rb_path}.orig"
+
+# Replace the target line to set the verbose option.
+sed -i -e 's/^V = .*/V = 1/' "${mkmf_rb_path}"
+
+# Print the difference between the original and modified file. This is useful
+# to debug when the `mkmf.rb` may change in the future. And check if the
+#`mkmf.rb` was modified. Because the `sed` command returns the exit status 0 no
+# matter it replaces successfully or not.
+if diff "${mkmf_rb_path}.orig" "${mkmf_rb_path}"; then
+  echo "error: ${mkmf_rb_path} was not modified." 1>&2
+  exit 1
+elif [ "${?}" != 1 ]; then
+  echo "error: diff was failed." 1>&2
+  exit 1
+fi