[#3731] Add version check and fallback to meson.sh

meson.sh

@@ -6,13 +6,46 @@
 # Usage: just like meson
 # Example: ./meson.sh setup build
 
+# Check if ${1} < ${2}.
+lt() {
+    # Sort numerically and check the first item.
+    lesser=$(printf '%s\n%s\n' "${1}" "${2}" | sort -V | head -n 1)
+    if test "${lesser}" = "${2}"; then
+        # ${1} >= ${2}
+        return 1
+    fi
+
+    # ${1} < ${2}
+    return 0
+}
+
 if test ! -d venv; then
-  python3 -m venv ./venv
-  ./venv/bin/pip install --upgrade pip
-  # When meson 1.8 will be released, we can pin the versions.
-  ./venv/bin/pip install git+https://github.com/mesonbuild/meson.git
-  ./venv/bin/pip install ninja
+    # Starting with Meson 0.62, Python 3.7 is required.
+    python3=python3
+    v=$(python3 -c 'import platform; print(platform.python_version())')
+    if lt "${v}" 3.7.0; then
+        # Search for a newer Python.
+        if command -V compgen >/dev/null; then
+            # shellcheck disable=SC3044
+            # SC3044 (warning): In POSIX sh, 'compgen' is undefined.
+            newer=$(compgen -c python3 | sort -V | tail -n 1)
+            if test -n "${newer}"; then
+                python3="${newer}"
+            fi
+        fi
+    fi
+
+    v=$("${python3}" -c 'import platform; print(platform.python_version())')
+    printf 'Python version: %s\n' "${v}"
+
+    "${python3}" -m venv ./venv
+    ./venv/bin/pip install --upgrade pip
+
+    # When meson 1.8 will be released, we can pin the versions.
+    ./venv/bin/pip install git+https://github.com/mesonbuild/meson.git
+    ./venv/bin/pip install ninja
 fi
+
 # shellcheck disable=SC1091
 # SC1091: Not following: ... was not specified as input (see shellcheck -x).
 . ./venv/bin/activate