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authorHeiko Voigt <hvoigt@hvoigt.net>2015-08-18 00:21:57 (GMT)
committerJunio C Hamano <gitster@pobox.com>2015-08-19 18:43:09 (GMT)
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submodule: implement a config API for lookup of .gitmodules values
In a superproject some commands need to interact with submodules. They need to query values from the .gitmodules file either from the worktree of from certain revisions. At the moment this is quite hard since a caller would need to read the .gitmodules file from the history and then parse the values. We want to provide an API for this so we have one place to get values from .gitmodules from any revision (including the worktree). The API is realized as a cache which allows us to lazily read .gitmodules configurations by commit into a runtime cache which can then be used to easily lookup values from it. Currently only the values for path or name are stored but it can be extended for any value needed. It is expected that .gitmodules files do not change often between commits. Thats why we lookup the .gitmodules sha1 from a commit and then either lookup an already parsed configuration or parse and cache an unknown one for each sha1. The cache is lazily build on demand for each requested commit. This cache can be used for all purposes which need knowledge about submodule configurations. Example use cases are: * Recursive submodule checkout needs to lookup a submodule name from its path when a submodule first appears. This needs be done before this configuration exists in the worktree. * The implementation of submodule support for 'git archive' needs to lookup the submodule name to generate the archive when given a revision that is not checked out. * 'git fetch' when given the --recurse-submodules=on-demand option (or configuration) needs to lookup submodule names by path from the database rather than reading from the worktree. For new submodule it needs to lookup the name from its path to allow cloning new submodules into the .git folder so they can be checked out without any network interaction when the user does a checkout of that revision. Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net> Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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+submodule config cache API
+==========================
+
+The submodule config cache API allows to read submodule
+configurations/information from specified revisions. Internally
+information is lazily read into a cache that is used to avoid
+unnecessary parsing of the same .gitmodule files. Lookups can be done by
+submodule path or name.
+
+Usage
+-----
+
+The caller can look up information about submodules by using the
+`submodule_from_path()` or `submodule_from_name()` functions. They return
+a `struct submodule` which contains the values. The API automatically
+initializes and allocates the needed infrastructure on-demand.
+
+If the internal cache might grow too big or when the caller is done with
+the API, all internally cached values can be freed with submodule_free().
+
+Data Structures
+---------------
+
+`struct submodule`::
+
+ This structure is used to return the information about one
+ submodule for a certain revision. It is returned by the lookup
+ functions.
+
+Functions
+---------
+
+`void submodule_free()`::
+
+ Use these to free the internally cached values.
+
+`const struct submodule *submodule_from_path(const unsigned char *commit_sha1, const char *path)`::
+
+ Lookup values for one submodule by its commit_sha1 and path.
+
+`const struct submodule *submodule_from_name(const unsigned char *commit_sha1, const char *name)`::
+
+ The same as above but lookup by name.
+
+For an example usage see test-submodule-config.c.