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add technical documentation about ref iteration
Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Documentation/technical/api-ref-iteration.txt
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Documentation/technical/api-ref-iteration.txt
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ref iteration API
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=================
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Iteration of refs is done by using an iterate function which will call a
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callback function for every ref. The callback function has this
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signature:
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int handle_one_ref(const char *refname, const unsigned char *sha1,
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int flags, void *cb_data);
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There are different kinds of iterate functions which all take a
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callback of this type. The callback is then called for each found ref
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until the callback returns nonzero. The returned value is then also
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returned by the iterate function.
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Iteration functions
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-------------------
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* `head_ref()` just iterates the head ref.
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* `for_each_ref()` iterates all refs.
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* `for_each_ref_in()` iterates all refs which have a defined prefix and
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strips that prefix from the passed variable refname.
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* `for_each_tag_ref()`, `for_each_branch_ref()`, `for_each_remote_ref()`,
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`for_each_replace_ref()` iterate refs from the respective area.
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* `for_each_glob_ref()` iterates all refs that match the specified glob
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pattern.
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* `for_each_glob_ref_in()` the previous and `for_each_ref_in()` combined.
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* `head_ref_submodule()`, `for_each_ref_submodule()`,
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`for_each_ref_in_submodule()`, `for_each_tag_ref_submodule()`,
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`for_each_branch_ref_submodule()`, `for_each_remote_ref_submodule()`
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do the same as the functions descibed above but for a specified
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submodule.
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* `for_each_rawref()` can be used to learn about broken ref and symref.
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* `for_each_reflog()` iterates each reflog file.
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Submodules
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----------
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If you want to iterate the refs of a submodule you first need to add the
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submodules object database. You can do this by a code-snippet like
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this:
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const char *path = "path/to/submodule"
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if (!add_submodule_odb(path))
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die("Error submodule '%s' not populated.", path);
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`add_submodule_odb()` will return an non-zero value on success. If you
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do not do this you will get an error for each ref that it does not point
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to a valid object.
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Note: As a side-effect of this you can not safely assume that all
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objects you lookup are available in superproject. All submodule objects
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will be available the same way as the superprojects objects.
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Example:
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--------
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----
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static int handle_remote_ref(const char *refname,
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const unsigned char *sha1, int flags, void *cb_data)
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{
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struct strbuf *output = cb_data;
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strbuf_addf(output, "%s\n", refname);
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return 0;
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}
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...
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struct strbuf output = STRBUF_INIT;
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for_each_remote_ref(handle_remote_ref, &output);
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printf("%s", output.buf);
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----
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