parametrise swift format binary (#285)

It can be useful to be able to control which binary is used for the
formatting soundness checks. This is particularly useful if someone
wanted to use this script locally to reproduce the formatting
check before committing and where they may have more than one binary
available.

Author: rnro

.github/workflows/scripts/check-swift-format.sh

@@ -17,23 +17,25 @@ log() { printf -- "** %s\n" "$*" >&2; }
 error() { printf -- "** ERROR: %s\n" "$*" >&2; }
 fatal() { error "$@"; exit 1; }
 
+SWIFT_FORMAT_BIN="${SWIFT_FORMAT_BIN:-$(which swift-format 2> /dev/null)}"; test -n "$SWIFT_FORMAT_BIN" || fatal "SWIFT_FORMAT_BIN unset and no swift-format on PATH"
+
 
 if [[ -f .swiftformatignore ]]; then
     log "Found swiftformatignore file..."
 
     log "Running swift-format format..."
-    tr '\n' '\0' < .swiftformatignore| xargs -0 -I% printf '":(exclude)%" '| xargs git ls-files -z '*.swift' | xargs -0 swift-format format --parallel --in-place
+    tr '\n' '\0' < .swiftformatignore| xargs -0 -I% printf '":(exclude)%" '| xargs git ls-files -z '*.swift' | xargs -0 "$SWIFT_FORMAT_BIN" format --parallel --in-place
 
     log "Running swift-format lint..."
 
-    tr '\n' '\0' < .swiftformatignore | xargs -0 -I% printf '":(exclude)%" '| xargs git ls-files -z '*.swift' | xargs -0 swift-format lint --strict --parallel
+    tr '\n' '\0' < .swiftformatignore | xargs -0 -I% printf '":(exclude)%" '| xargs git ls-files -z '*.swift' | xargs -0 "$SWIFT_FORMAT_BIN" lint --strict --parallel
 else
     log "Running swift-format format..."
-    git ls-files -z '*.swift' | xargs -0 swift-format format --parallel --in-place
+    git ls-files -z '*.swift' | xargs -0 "$SWIFT_FORMAT_BIN" format --parallel --in-place
 
     log "Running swift-format lint..."
 
-    git ls-files -z '*.swift' | xargs -0 swift-format lint --strict --parallel
+    git ls-files -z '*.swift' | xargs -0 "$SWIFT_FORMAT_BIN" lint --strict --parallel
 fi