ci-fairy: add a --verify command to generate-template

A number of projects have a job that runs generate-template followed by a diff
to make sure the generated file is the one checked in. Let's remove the manual
diff step from that and provide it as built-in functionality from ci-fairy.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
[re-run generate_templates.py after rebase]
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>

.gitlab-ci.yml

@@ -206,7 +206,7 @@ test published images:
   script:
     - skopeo inspect docker://quay.io/freedesktop.org/ci-templates:buildah-aarch64-2020-10-30.1
     - skopeo inspect docker://quay.io/freedesktop.org/ci-templates:buildah-x86_64-2020-10-30.1
-    - skopeo inspect docker://quay.io/freedesktop.org/ci-templates:ci-fairy-sha256-8dfd966d36784771d67cdfca46bfe23ae7a320cbed3fb5c6f883508bd8d157c0
+    - skopeo inspect docker://quay.io/freedesktop.org/ci-templates:ci-fairy-sha256-f35ed97d970ffc3c1447bf388756ed6d54cc8e662f01718cb71aef2f650acece
     - skopeo inspect docker://quay.io/freedesktop.org/ci-templates:qemu-base-x86_64-2020-10-30.1
     - skopeo inspect docker://quay.io/freedesktop.org/ci-templates:qemu-mkosi-base-x86_64-2020-10-30.1
   rules:

.gitlab-ci/ci-fairy-ci.yml

@@ -14,7 +14,7 @@ ci-fairy-base-image:
 
 .ci-fairy-tag:
   variables:
-    FDO_DISTRIBUTION_TAG: sha256-8dfd966d36784771d67cdfca46bfe23ae7a320cbed3fb5c6f883508bd8d157c0
+    FDO_DISTRIBUTION_TAG: sha256-f35ed97d970ffc3c1447bf388756ed6d54cc8e662f01718cb71aef2f650acece
 
 # The actual ci-fairy image with ci-fairy installed
 # This image uses the sha of the ci-fairy script itself as tag.

templates/ci-fairy.yml

@@ -31,6 +31,6 @@
 # Variables provided by this template should be considered read-only.
 #
 .fdo.ci-fairy:
-  image: quay.io/freedesktop.org/ci-templates:ci-fairy-sha256-8dfd966d36784771d67cdfca46bfe23ae7a320cbed3fb5c6f883508bd8d157c0
+  image: quay.io/freedesktop.org/ci-templates:ci-fairy-sha256-f35ed97d970ffc3c1447bf388756ed6d54cc8e662f01718cb71aef2f650acece
   variables:
-    FDO_DISTRIBUTION_IMAGE: quay.io/freedesktop.org/ci-templates:ci-fairy-sha256-8dfd966d36784771d67cdfca46bfe23ae7a320cbed3fb5c6f883508bd8d157c0
\ No newline at end of file
+    FDO_DISTRIBUTION_IMAGE: quay.io/freedesktop.org/ci-templates:ci-fairy-sha256-f35ed97d970ffc3c1447bf388756ed6d54cc8e662f01718cb71aef2f650acece
\ No newline at end of file

tools/ci_fairy.py

@@ -9,6 +9,7 @@ import git
 import gitdb
 import gitlab
 from gitlab import Gitlab
+import io
 import jinja2
 import json
 import fnmatch
@@ -855,9 +856,10 @@ def lint(ctx, filename):
 @click.option('--config', help='YAML configuration file', required=False)
 @click.option('--root', help='YAML node to use as root node', type=str)
 @click.option('--output-file', '-o', help='output file to write to (default: stdout)')
+@click.option('--verify', is_flag=True, help='Compare the generated file against the existing one and fail if they differ')
 @click.argument('template', required=False)
 @click.pass_context
-def generate_template(ctx, config, root, template, output_file):
+def generate_template(ctx, config, root, template, output_file, verify):
     '''
     Generate a file based on the given Jinja2 template and the YAML
     configuration file.
@@ -872,6 +874,10 @@ def generate_template(ctx, config, root, template, output_file):
     Where the --root option is specified, the children of that root node are
     the data to be used in the template. For nested root nodes, use
     /path/to/node.
+
+    Where the --verify option is given, the output file is not overwritten.
+    Instead, ci-fairy compares the newly generated to the existing output
+    file and exits with an error if the two differs.
     '''
 
     if template is None:
@@ -898,9 +904,10 @@ def generate_template(ctx, config, root, template, output_file):
         sys.exit(1)
 
     if output_file is None:
-        output_file = sys.stdout
+        outfile = sys.stdout
+        output_file = 'stdout'
     else:
-        output_file = open(Path(output_file), 'w')
+        outfile = open(Path(output_file), 'r' if verify else 'w')
 
     if configfile == '-':
         fd = sys.stdin
@@ -925,7 +932,41 @@ def generate_template(ctx, config, root, template, output_file):
                              extensions=['jinja2.ext.do'])
     env.globals["ci_fairy"] = _env_ci_fairy
     template = env.get_template(templatefile.name)
-    template.stream(data).dump(output_file)
+    if verify:
+        import difflib
+        # both need to be in format [ 'line1\n', 'line2\n', ...]
+        newfile = [f'{l}\n' for l in template.render(data).split('\n')]
+        oldfile = outfile.readlines()
+        diff = difflib.unified_diff(oldfile,
+                                    newfile,
+                                    tofile=f'{output_file} (generated)',
+                                    fromfile=output_file)
+
+        red = ''
+        green = ''
+        reset = ''
+        try:
+            if os.isatty(sys.stdout.fileno()):
+                red = colored.fg('red')
+                green = colored.fg('green')
+                reset = colored.attr('reset')
+        # pytest replaces sys.stdout and throws an exception on fileno()
+        except io.UnsupportedOperation:
+            pass
+
+        for l in diff:
+            if l[0] == '-':
+                prefix = red
+            elif l[0] == '+':
+                prefix = green
+            else:
+                prefix = ''
+            print(f'{prefix}{l}{reset}', end='')
+
+        if diff:
+            sys.exit(1)
+    else:
+        template.stream(data).dump(outfile)
 
 
 @ci_fairy.command()

tools/test_ci_fairy.py

@@ -534,6 +534,31 @@ def test_template_ci_fairy_hashfiles():
                                 'file7: dbc23bd9d9e6d52829aefdca4da566620337c2136b7942af85b6e21f664f7684'
 
 
+def test_template_verify():
+    runner = CliRunner()
+    with runner.isolated_filesystem():
+        with open('test.yml', 'w') as fd:
+            fd.write(DEFAULT_YAML)
+        with open('test.tmpl', 'w') as fd:
+            fd.write('three is {{numbers.three}}\n')
+            fd.write('line to be removed\n')
+
+        # generate the first file
+        args = ['generate-template', '--config', 'test.yml', '--output-file', 'outfile', 'test.tmpl']
+        result = runner.invoke(ci_fairy.ci_fairy, args)
+
+        with open('test.tmpl', 'w') as fd:
+            fd.write('three is {{numbers.three}}\n')
+            fd.write('added line\n')
+
+        args.append('--verify')
+        result = runner.invoke(ci_fairy.ci_fairy, args)
+        assert result.exit_code == 1
+        print(result.stdout)
+        assert '-line to be removed' in result.stdout
+        assert '+added line' in result.stdout
+
+
 def test_commits_needs_git_repo(caplog):
     runner = CliRunner()
     with runner.isolated_filesystem():