build: Enforce gofmt on all Go sources

Gofmt returns with an exit code of 0 even when it's not happy with the
formatting of the source files. The recommendation is to check the
emptyness of the output [1].

[1] https://github.com/golang/go/issues/24230

https://github.com/containers/toolbox/pull/983

src/meson.build

@@ -1,6 +1,8 @@
 go_build_wrapper_file = files('go-build-wrapper')
 go_build_wrapper_program = find_program('go-build-wrapper')
 
+meson_go_fmt_program = find_program('meson_go_fmt.py')
+
 sources = files(
   'toolbox.go',
   'cmd/create.go',
@@ -66,4 +68,5 @@ if shellcheck.found()
   test('shellcheck go-build-wrapper', shellcheck, args: [go_build_wrapper_file])
 endif
 
+test('go fmt', meson_go_fmt_program, args: [meson.current_source_dir()])
 test('toolbox go unit tests', go, args: ['test', '-v', './...'], workdir: meson.current_source_dir())

src/meson_go_fmt.py

@@ -0,0 +1,39 @@
+#!/usr/bin/env python3
+#
+# Copyright © 2022 Red Hat Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import subprocess
+import sys
+
+if len(sys.argv) != 2:
+    print('{}: wrong arguments'.format(sys.argv[0]), file=sys.stderr)
+    print('Usage: {} [SOURCE DIR]'.format(sys.argv[0]), file=sys.stderr)
+    sys.exit(1)
+
+source_dir = sys.argv[1]
+
+try:
+    gofmt = subprocess.run(['gofmt', '-d', source_dir], capture_output=True, check=True)
+except subprocess.CalledProcessError as e:
+    print('{}: gofmt returned non-zero exit status {}'.format(sys.argv[0], e.returncode), file=sys.stderr)
+    sys.exit(e.returncode)
+
+if gofmt.stdout:
+   diff = gofmt.stdout.decode()
+   print(diff)
+   sys.exit(1)
+
+sys.exit(0)