Add minimal as a possible input for gap-version

.github/workflows/CI.yml

@@ -32,6 +32,9 @@ jobs:
           - os: macos-latest
             configflags: '--with-gmp=builtin'
         include:
+          - os: ubuntu-latest
+            gap-version: minimal
+            configflags: ''
           - os: ubuntu-latest
             gap-version: latest
             configflags: ''
@@ -49,15 +52,23 @@ jobs:
             configflags: ''
 
     steps:
+      - name: "Clone the Example package"
+        uses: actions/checkout@v7
+        if: ${{ matrix.gap-version == 'minimal' }}
+        with:
+          repository: gap-packages/example
+
       - name: "Checkout"
         uses: actions/checkout@v7
+        with:
+          path: this-action/
 
       - name: "Setup Cygwin"
         if: ${{ matrix.os == 'windows-latest' }}
         uses: gap-actions/setup-cygwin@v2
 
       - name: "Setup GAP"
-        uses: ./
+        uses: ./this-action/
         with:
           gap-version: ${{ matrix.gap-version }}
           configflags: ${{ matrix.configflags }}

README.md

@@ -22,7 +22,8 @@ Its behaviour can be customized via the inputs below.
 All of the following inputs are optional.
 
 - `gap-version`:
-   - The gap version or branch to build. You may specify "latest" for the latest release, or "devel" for the development version.
+   - The gap version or branch to build. You may specify "latest" for the latest release, "devel" for the development version,
+     or "minimal" for the minimal version supported by the GAP package in the current directory.
      See "Changes to inputs" under "What's new in v3" for more details.
    - default: `latest`
 - `repository`
@@ -40,6 +41,8 @@ you will have to change the inputs accordingly. We also recommend replacing bran
  - The `GAPBRANCH` input has been replaced by `gap-version`, which accepts the following input types:
    - `latest`: this will use the latest release of GAP. This will **not** point to the latest pre-release if it is more recent
      than the latest release.
+   - `minimal`: this will use oldest version of GAP that is supported by both the GAP package in the current directory, and this
+     action (which currently means GAP 4.9).
    - version numbers: e.g. `v4.14.0`, `v4.15.0-beta1`, etc. The leading `v` is optional, the oldest available release is `v4.10.0`.
    - incomplete version numbers: e.g. `v4`, `v4.10`, etc. These will be expanded to the most recent release starting with the incomplete
      version number, e.g. `v4.10` is equivalent to `v4.10.2`. This will **not** expand to pre-releases, and again the leading `v` is

action.yml

@@ -89,6 +89,8 @@ runs:
     - name: "Determine GAP version"
       id: version
       shell: bash
+      env:
+        OLDEST_VER: "4.9"
       run: |
         VERSION=""
         IS_RELEASE=true
@@ -104,8 +106,34 @@ runs:
             GIT_RELS=$(cat $RUNNER_TEMP/gap_releases.json | jq -r '.[].tagName' | sort -V)
             GIT_NPRS=$(cat $RUNNER_TEMP/gap_releases.json | jq -r '.[] | select(.isPrerelease == false) | .tagName' | sort -V)
 
-            # Add "v" in front if missing
             REL=${{ inputs.gap-version }}
+            if [[ "$REL" == "minimal" ]]; then
+              # Attempt to extract the minimal support GAP version from
+              # PackageInfo.g via a regex (while in theory this can not always
+              # work, in practice it does work quite well)
+              REGEX="GAP[[:space:]]*:=[[:space:]]*\"([^\"]*)\""
+
+              if [[ ! -f "PackageInfo.g" ]]; then
+                echo "::error::Could not find PackageInfo.g."
+                exit 1
+              elif [[ $(cat PackageInfo.g) =~ ${REGEX} ]]; then
+                # Get from capture group in regex
+                PKG_VER="${BASH_REMATCH[1]}"
+                echo "Version: PackageInfo.g contains \"${PKG_VER}\""
+
+                # Remove leading stuff if present
+                PKG_VER=${PKG_VER##*[>= ]}
+
+                # Ensure the extracted version is not below the oldest GAP version supported by this GAP acttion
+                REL=$(printf '%s\n' "${PKG_VER}" "${OLDEST_VER}" | sort -V | tail -n1)
+                echo "Version: turned \"${PKG_VER}\" into \"${REL}\""
+              else
+                echo "::error::Could not extract minimal supported version from PackageInfo.g."
+                exit 1
+              fi
+            fi
+
+            # Ensure a "v" is in front
             REL=v${REL#v}
 
             if echo "$GIT_RELS" | grep -qx "$REL" ; then