meson: wire up static analysis via Coccinelle

Wire up static analysis via Coccinelle via a new test target
"coccicheck". This target can be executed via `meson compile coccicheck`
and generates the semantic patch for us.

Note that we don't hardcode the list of source and header files that
shall be analyzed, and instead use git-ls-files(1) to find them for us.
This is because we also want to analyze files that may not get built on
the current platform, so finding all sources at configure time is easier
than introducing a new variable that tracks all sources, including those
which aren't being built.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/coccinelle/meson.build

@@ -0,0 +1,89 @@
+spatch = find_program('spatch', required: get_option('coccinelle'))
+if not spatch.found()
+  subdir_done()
+endif
+
+third_party_sources = [
+  ':!contrib',
+  ':!compat/inet_ntop.c',
+  ':!compat/inet_pton.c',
+  ':!compat/nedmalloc',
+  ':!compat/obstack.*',
+  ':!compat/poll',
+  ':!compat/regex',
+  ':!sha1collisiondetection',
+  ':!sha1dc',
+  ':!t/unit-tests/clar',
+  ':!t/unit-tests/clar',
+  ':!t/t[0-9][0-9][0-9][0-9]*',
+]
+
+rules = [
+  'array.cocci',
+  'commit.cocci',
+  'config_fn_ctx.pending.cocci',
+  'equals-null.cocci',
+  'flex_alloc.cocci',
+  'free.cocci',
+  'git_config_number.cocci',
+  'hashmap.cocci',
+  'index-compatibility.cocci',
+  'object_id.cocci',
+  'preincr.cocci',
+  'qsort.cocci',
+  'refs.cocci',
+  'strbuf.cocci',
+  'swap.cocci',
+  'the_repository.cocci',
+  'xcalloc.cocci',
+  'xopen.cocci',
+  'xstrdup_or_null.cocci',
+  'xstrncmpz.cocci',
+]
+
+concatenated_rules = custom_target(
+  command: [
+    'cat', '@INPUT@',
+  ],
+  input: rules,
+  output: 'rules.cocci',
+  capture: true,
+)
+
+sources = [ ]
+foreach source : run_command(git, '-C', meson.project_source_root(), 'ls-files', '--deduplicate', '*.c', third_party_sources, check: true).stdout().split()
+  sources += source
+endforeach
+
+headers = [ ]
+foreach header : run_command(git, '-C', meson.project_source_root(), 'ls-files', '--deduplicate', '*.h', third_party_sources, check: true).stdout().split()
+  headers += meson.project_source_root() / header
+endforeach
+
+patches = [ ]
+foreach source : sources
+  patches += custom_target(
+    command: [
+      spatch,
+      '--all-includes',
+      '--sp-file', concatenated_rules,
+      '--patch', meson.project_source_root(),
+      '@INPUT@',
+    ],
+    input: meson.project_source_root() / source,
+    output: source.underscorify() + '.patch',
+    capture: true,
+    depend_files: headers,
+  )
+endforeach
+
+concatenated_patch = custom_target(
+  command: [
+    'cat', '@INPUT@',
+  ],
+  input: patches,
+  output: 'cocci.patch',
+  capture: true,
+)
+
+alias_target('coccicheck', concatenated_patch)

contrib/meson.build

@@ -2,4 +2,5 @@ foreach feature : get_option('contrib')
   subdir(feature)
 endforeach
 
+subdir('coccinelle')
 subdir('credential')

meson_options.txt

@@ -101,6 +101,8 @@ option('docs_backend', type: 'combo', choices: ['asciidoc', 'asciidoctor', 'auto
   description: 'Which backend to use to generate documentation.')
 
 # Testing.
+option('coccinelle', type: 'feature', value: 'auto',
+  description: 'Provide a coccicheck target that generates a Coccinelle patch.')
 option('tests', type: 'boolean', value: true,
   description: 'Enable building tests. This requires Perl, but is separate from the "perl" option such that you can build tests without Perl features enabled.')
 option('test_output_directory', type: 'string',