tools/bump: run the pre-commit hooks before opening the pull request

make fmt does not cover nixpkgs-fmt, trailing whitespace, end-of-file or
the YAML checks, and the bot rewrites workflow files and Dockerfiles.

tools/bump/area.go

@@ -90,14 +90,13 @@ func allAreas() []area {
 		Message: func(change) string { return "all: regenerate generated files" },
 	})
 
-	// Last, so it also covers whatever the generators emitted. nixpkgs decides
-	// which prettier and gofumpt the tree is formatted with, so a lock bump can
-	// reformat files no other area went near.
+	// Last, so it also covers whatever the generators emitted, and so the
+	// pre-commit hooks judge the finished tree rather than an intermediate one.
 	return append(areas, area{
 		Name:    "fmt",
 		Needs:   []string{"flake"},
 		Apply:   applyFormat,
-		Message: func(change) string { return "all: apply the formatters from the new toolchain" },
+		Message: func(change) string { return "all: satisfy the formatters and pre-commit hooks" },
 	})
 }
 

tools/bump/generate.go

@@ -130,15 +130,26 @@ func gateGenerate(ctx context.Context, r *repo) error {
 	return nil
 }
 
-// applyFormat re-runs the repository formatters. A toolchain bump can change
-// what "formatted" means: a newer prettier out of nixpkgs reformats files no
-// bump touched, and the formatting check then fails on a tree the bot never
-// edited. Running last means it also tidies whatever the generators emitted.
+// applyFormat re-runs everything that decides whether the tree is acceptable to
+// CI, and commits whatever it rewrites. Two reasons it cannot be skipped:
+// nixpkgs picks which prettier and gofumpt the tree is formatted with, so a
+// lock bump reformats files no area touched; and the bot rewrites workflow YAML
+// and Dockerfiles, where a stray trailing space or an unformatted .nix fails a
+// hook rather than the compiler.
+//
+// The first hook pass is expected to fail, because a hook that rewrites a file
+// reports failure. The second pass is the real verdict.
 func applyFormat(ctx context.Context, r *repo) (change, error) {
 	if _, err := r.nixRun(ctx, "make", "fmt"); err != nil { //nolint:noinlineerr
 		return change{}, err
 	}
 
+	_, _ = r.nixRun(ctx, "prek", "run", "--all-files")
+
+	if _, err := r.nixRun(ctx, "prek", "run", "--all-files"); err != nil { //nolint:noinlineerr
+		return change{}, err
+	}
+
 	touched, err := changedFiles(ctx, r)
 	if err != nil {
 		return change{}, err