Wiring up coccinelle in the build, depends on running git commands to
get the list of files to operate on. Reasonable, for a feature mainly
used by people developing on git. If building git itself from a tarball
distribution of git's own source code, one likely does not need to run
coccinelle.

But running those git commands failed, and caused the build to error
out, if `spatch` was installed -- because the build assumed that its
presence indicated a desire to use it on this source tree. Instead, we
can expand the conditional to check for both `spatch` and the `.git`
file or directory.

Meson's `opt.require()` method allows us to add a prerequisite for the
feature option. If the prerequisite fails, then the option either:

- converts autodetection to disabled

- emits an informative error if the feature was set to enabled:

  ERROR: Feature coccinelle cannot be enabled: coccinelle can only be run from a git checkout

Signed-off-by: Eli Schwartz <redacted>
---

v2: accidentally chopped off part of the commit message, sorry...

 contrib/coccinelle/meson.build | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/contrib/coccinelle/meson.build b/contrib/coccinelle/meson.build
index 5d76a7fee6..ea054c924f 100644
--- a/contrib/coccinelle/meson.build
+++ b/contrib/coccinelle/meson.build

@@ -1,4 +1,9 @@
-spatch = find_program('spatch', required: get_option('coccinelle'))
+coccinelle_opt = get_option('coccinelle').require(
+  fs.exists(meson.project_source_root() / '.git'),
+  error_message: 'coccinelle can only be run from a git checkout',
+)
+
+spatch = find_program('spatch', required: coccinelle_opt)
 if not spatch.found()
   subdir_done()
 endif

base-commit: c1d6628c9433c09ff62f916f2b933ee12995e9d8
-- 
2.48.1