ci: Check and confirm Vim feature flags exist before testing

Vim tests for features such as python3 relies on checking the feature
flag exists by doing `has('python3')`. However, if the feature itself is
broken and the flag returns 0, the relevant tests will simply silently
get ignored and CI will passed erroneously. As a preventive measure, as
basic checks to make sure certain feature flags are correct as a basic
smoke test.

Currently only checking two types of feature flags:

1. Features that depend on system packages being installed properly
   (e.g. sodium) and could be erroneously dropped if the CI environment
   changed or a bug exists in the configure script.
2. Scripting languages. When in dynamic mode, these feature flags (e.g.
   "ruby", "python3") will return 0 when the lib cannot be found or the
   code has an initialization bug. This happened in #16964 where CI
   still passed despite Python 3 being broken.

closes: #16998

Signed-off-by: Yee Cheng Chin <ychin.git@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

.github/workflows/ci.yml

@@ -266,6 +266,12 @@ jobs:
           "${SRCDIR}"/vim --version
           "${SRCDIR}"/vim -u NONE -i NONE --not-a-term -esNX -V1 -S ci/if_ver-1.vim -c quit
           "${SRCDIR}"/vim -u NONE -i NONE --not-a-term -esNX -V1 -S ci/if_ver-2.vim -c quit
+          if ${{ matrix.features == 'huge' }}; then
+            # Also check that optional and dynamic features are configured and working
+            "${SRCDIR}"/vim -u NONE -i NONE --not-a-term -esNX -V1 \
+              -c "let g:required=['gettext', 'sodium', 'sound', 'perl', 'python3', 'lua', 'ruby', 'tcl']" \
+              -S ci/if_feat_check.vim -c quit
+          fi
 
       - name: Test
         if: matrix.architecture != 'arm64'
@@ -392,6 +398,12 @@ jobs:
           "${SRCDIR}"/vim --version
           "${SRCDIR}"/vim -u NONE -i NONE --not-a-term -esNX -V1 -S ci/if_ver-1.vim -c quit
           "${SRCDIR}"/vim -u NONE -i NONE --not-a-term -esNX -V1 -S ci/if_ver-2.vim -c quit
+          if ${{ matrix.features == 'huge' }}; then
+            # Also check that optional and dynamic features are configured and working
+            "${SRCDIR}"/vim -u NONE -i NONE --not-a-term -esNX -V1 \
+              -c "let g:required=['sound', 'perl', 'python3', 'lua', 'ruby', 'tcl']" \
+              -S ci/if_feat_check.vim -c quit
+          fi
 
       - name: Install packages for testing
         run: |
@@ -663,6 +675,11 @@ jobs:
             src\vim --version || exit 1
             src\vim -u NONE -i NONE --not-a-term -esNX -V1 -S ci/if_ver-1.vim -c quit
             src\vim -u NONE -i NONE --not-a-term -esNX -V1 -S ci/if_ver-2.vim -c quit
+            if "${{ matrix.features }}"=="HUGE" (
+              src\vim -u NONE -i NONE --not-a-term -esNX -V1 ^
+                -c "let g:required=['gettext', 'sodium', 'sound', 'python3', 'lua']" ^
+                -S ci/if_feat_check.vim -c quit
+            )
           )
 
       #- name: Prepare Artifact