README
1This directory provides examples of Coccinelle (http://coccinelle.lip6.fr/)
2semantic patches that might be useful to developers.
3
4There are two types of semantic patches:
5
6 * Using the semantic transformation to check for bad patterns in the code;
7 The target 'make coccicheck' is designed to check for these patterns and
8 it is expected that any resulting patch indicates a regression.
9 The patches resulting from 'make coccicheck' are small and infrequent,
10 so once they are found, they can be sent to the mailing list as per usual.
11
12 Example for introducing new patterns:
13 67947c34ae (convert "hashcmp() != 0" to "!hasheq()", 2018-08-28)
14 b84c783882 (fsck: s/++i > 1/i++/, 2018-10-24)
15
16 Example of fixes using this approach:
17 248f66ed8e (run-command: use strbuf_addstr() for adding a string to
18 a strbuf, 2018-03-25)
19 f919ffebed (Use MOVE_ARRAY, 2018-01-22)
20
21 These types of semantic patches are usually part of testing, c.f.
22 0860a7641b (travis-ci: fail if Coccinelle static analysis found something
23 to transform, 2018-07-23)
24
25 * Using semantic transformations in large scale refactorings throughout
26 the code base.
27
28 When applying the semantic patch into a real patch, sending it to the
29 mailing list in the usual way, such a patch would be expected to have a
30 lot of textual and semantic conflicts as such large scale refactorings
31 change function signatures that are used widely in the code base.
32 A textual conflict would arise if surrounding code near any call of such
33 function changes. A semantic conflict arises when other patch series in
34 flight introduce calls to such functions.
35
36 So to aid these large scale refactorings, semantic patches can be used.
37 However we do not want to store them in the same place as the checks for
38 bad patterns, as then automated builds would fail.
39 That is why semantic patches 'contrib/coccinelle/*.pending.cocci'
40 are ignored for checks, and can be applied using 'make coccicheck-pending'.
41
42 This allows to expose plans of pending large scale refactorings without
43 impacting the bad pattern checks.
44