Honor a cache-restored build when a versioned extension mismatches (#1108)

* fix: honor a cache-restored build when a versioned extension mismatches

When a PHP package install bundles its own default build of a versioned
extension (e.g. redis ships with its own recent version pre-enabled),
add_pecl_extension correctly detects the version mismatch against the
pinned version and falls back to pecl_install - but it does this even
when a matching build has already been restored from a CI cache into a
separate directory, since shared_extension only checks that *some* file
exists at ext_dir, not which version it is.

This adds an opt-in CACHED_EXTENSIONS_DIR: when set and a mismatch is
detected, look for extension.so there, and if found, copy it into
ext_dir and re-check before falling back to a full pecl_install. When
CACHED_EXTENSIONS_DIR is unset, behavior is unchanged.

Related to shivammathur/cache-extensions#21 and #37, where a cached
build of a versioned PECL extension is silently ignored and
recompiled on every run regardless of caching.

* fix: preserve versioned builds in ext_dir instead of a separate cache dir

Per @shivammathur's review on the PR: drop the opt-in
CACHED_EXTENSIONS_DIR env var. Instead, after installing a versioned
extension, keep a second copy of the built .so in ext_dir itself under
a name with no .so suffix (e.g. redis-5.3.7), so it can't be mistaken
for the active extension and rides along in the same ext_dir that
cache-extensions already caches wholesale - no separate cache
directory, key, or workflow step required. On a version mismatch,
restore that preserved build over the active binary and re-check
before falling back to a full pecl_install.

src/scripts/extensions/add_extensions.sh

@@ -214,12 +214,36 @@ add_pecl_extension() {
     pecl_version=$(get_pecl_version "$extension" "$pecl_version")
   fi
   ext_version=$(php -r "echo phpversion('$extension');")
+  # The PHP package install itself can bundle its own default build of a
+  # versioned extension (e.g. redis ships with its own recent version),
+  # which overwrites ext_dir/$extension.so before this function ever runs.
+  # shared_extension only checks that *a* file exists, not which version, so
+  # a build matching the pinned version - even one cache-extensions already
+  # restored into ext_dir - never gets a chance: this always fell straight
+  # through to pecl_install regardless of caching. Preserve built versions
+  # in ext_dir itself under a name with no .so suffix, so cache-extensions
+  # (which caches all of ext_dir) picks them up automatically, and the PHP
+  # package install's own file can't collide with or overwrite them. On a
+  # mismatch, restore the matching preserved build before falling back to a
+  # full pecl_install.
+  if [ -n "$pecl_version" ] && check_extension "$extension" && [ "${ext_version/-/}" != "$pecl_version" ]; then
+    preserved="${ext_dir:?}/$extension-$pecl_version"
+    if [ -e "$preserved" ]; then
+      disable_extension_helper "$extension" >/dev/null 2>&1
+      sudo cp "$preserved" "${ext_dir:?}/$extension.so"
+      enable_extension "$extension" "$prefix"
+      ext_version=$(php -r "echo phpversion('$extension');")
+    fi
+  fi
   if check_extension "$extension" && [[ -z "$pecl_version" || (-n "$pecl_version" && "${ext_version/-/}" == "$pecl_version") ]]; then
     add_log "${tick:?}" "$extension" "Enabled"
   else
     [ -n "$pecl_version" ] && pecl_version="-$pecl_version"
     pecl_install "$extension$pecl_version" || ( [ "${fail_fast:?}" = "false" ] && add_extension "$extension" "$(get_extension_prefix "$extension")" >/dev/null 2>&1)
     extension_version="$(php -r "echo phpversion('$extension');")"
+    if check_extension "$extension" && [ -n "$extension_version" ]; then
+      sudo cp "${ext_dir:?}/$extension.so" "${ext_dir:?}/$extension-$extension_version" 2>/dev/null || true
+    fi
     [ -n "$extension_version" ] && extension_version="-$extension_version"
     add_extension_log "$extension$extension_version" "Installed and enabled"
   fi