add Makefile targets for fix-whitespace

`make whitespace` now runs `fix-whitespace --check --verbose` and
`make fix-whitespace` runs `fix-whitespace --verbose`.

.github/workflows/whitespace.yml

@@ -7,8 +7,21 @@ on:
 
 jobs:
   whitespace:
+    defaults:
+      run:
+        shell: bash
     runs-on: ubuntu-latest
 
     steps:
+
     - uses: actions/checkout@v4
-    - uses: andreasabel/fix-whitespace-action@v1
+
+    - run: |
+        # no longer using the action because apparently we're supposed to use the Makefile here
+        wget -q https://github.com/agda/fix-whitespace/releases/download/v0.1/fix-whitespace-0.1-linux.binary
+        mkdir -p "$HOME/.local/bin"
+        mv fix-whitespace-0.1-linux.binary "$HOME/.local/bin/fix-whitespace"
+        chmod +x "$HOME/.local/bin/fix-whitespace"
+        echo "$HOME/.local/bin" >> $GITHUB_PATH
+
+    - run: make whitespace

CONTRIBUTING.md

@@ -191,7 +191,9 @@ Whitespace Conventions
 
 We use automated whitespace convention checking. Violations can be fixed by
 running [fix-whitespace](https://hackage.haskell.org/package/fix-whitespace). If
-you push a fix of a whitespace violation, please do so in a _separate commit_.
+you push a fix of a whitespace violation, please do so in a _separate commit_. For convenience,
+`make whitespace` will show violations and `make fix-whitespace` will fix them, if the
+`fix-whitespace` utility is installed.
 
 Other Conventions
 -----------------

Makefile

@@ -41,6 +41,14 @@ style-commit: ## Run the code styler on the previous commit
 	@git diff --name-only HEAD $(COMMIT) Cabal Cabal-syntax cabal-install \
 		| grep '.hs$$' | xargs -P $(PROCS) -I {} fourmolu -q -i {}
 
+.PHONY: whitespace
+whitespace: ## Run fix-whitespace in check mode
+	fix-whitespace --check --verbose
+
+.PHONY: fix-whitespace
+fix-whitespace: ## Run fix-whitespace in fix mode
+	fix-whitespace --verbose
+
 # source generation: SPDX
 
 SPDX_LICENSE_HS:=Cabal-syntax/src/Distribution/SPDX/LicenseId.hs