| Message ID | xmqq4jdxmx2e.fsf@gitster.g (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | doc: clarify the wording on <git-compat-util.h> requirement | expand |
On Sat, Feb 24, 2024 at 12:22 PM Junio C Hamano <gitster@pobox.com> wrote: > > The reason why we insist including the compat-util header as the > very first thing is because it is our mechanism to absorb the > differences across platforms, like the order in which system header > files must be included, and C preprocessor feature macros that are > needed to trigger certain features we want out of the systems, and > insulate other headers and sources from such minutiae. > > Earlier we tried to clarify the rule in the coding guidelines > document, but the wording was a bit fuzzy that can lead to > misinterpretations like you can include xdiff/xinclude.h only to > avoid having to include git-compat-util.h file even if you have > nothing to do with xdiff implementation, for example. "You do not > have to include more than one of these" were also misleading and > would have been puzzling if you _needed_ to depend on more than one > of these approved headers (answer: you are allowed to include them > all if you need the declarations in them for reasons other than that > you want to avoid including compat-util yourself). > > Instead of using the phrase "approved headers", enumerate them as > exceptions, each labeled with intended audiences, to avoid such > misinterpretations. The structure also makes it easier to add new > exceptions, so add the description of "t/unit-tests/test-lib.h" > being an exception only for the unit tests implementation as an > example. > > Signed-off-by: Junio C Hamano <gitster@pobox.com> > --- > > * git-std-lib folks CC'ed to show them where to put their exception > when things start to stabilize; Elijah CC'ed for his 8bff5ca0 > (treewide: ensure one of the appropriate headers is sourced > first, 2023-02-24) and bc5c5ec0 (cache.h: remove this > no-longer-used header, 2023-05-16). > > Documentation/CodingGuidelines | 30 ++++++++++++++++++++++++------ > 1 file changed, 24 insertions(+), 6 deletions(-) > > diff --git c/Documentation/CodingGuidelines w/Documentation/CodingGuidelines > index 578587a471..b3443dd773 100644 > --- c/Documentation/CodingGuidelines > +++ w/Documentation/CodingGuidelines > @@ -446,12 +446,30 @@ For C programs: > detail. > > - The first #include in C files, except in platform specific compat/ > - implementations and sha1dc/, must be either "git-compat-util.h" or > - one of the approved headers that includes it first for you. (The > - approved headers currently include "builtin.h", > - "t/helper/test-tool.h", "xdiff/xinclude.h", or > - "reftable/system.h".) You do not have to include more than one of > - these. > + implementations and sha1dc/, must be "git-compat-util.h". In > + addition: This "In addition" ties to the "are allowed to" 19 lines below, which was confusing for me until I intentionally ignored the "In addition", continued reading, and finally caught the other piece of it. Perhaps either `Exceptions:`, or something like `The following cases are allowed to assume that their header file includes "git-compat-util.h", and they do not have to include "git-compat-util.h" themselves:` -- I have a slight preference for the latter form, but I worry that the "These headers must be the first header file to be "#include"d in them" bit will be missed. So maybe if we went with the latter version, we change each bullet point to include that qualification. Example: - the implementation of the built-in commands in the "builtin/" directory that include "builtin.h" as the first header". I don't know if we need the reasoning why you'd #include these files in the bullets below, which is why I didn't include it here. I'm assuming there's a concern about implying that builtin/foo.c should include builtin.h instead of git-compat-util.h (even if foo.c doesn't use cmd_foo()?). > + > + - the implementation of the built-in commands in the "builtin/" > + directory that include "builtin.h" for the cmd_foo() prototype > + definition > + > + - the test helper programs in the "t/helper/" directory that include > + "t/helper/test-tool.h" for the cmd__foo() prototype definition > + > + - the xdiff implementation in the "xdiff/" directory that includes > + "xdiff/xinclude.h" for the xdiff machinery internals > + > + - the unit test programs in "t/unit-tests/" directory that include > + "test-lib.h" that gives them the unit-tests framework > + > + - the source files that implement reftable in the "reftable/" > + directory that include "reftable/system.h" for the reftable > + internals > + > + are allowed to assume that their header file includes > + "git-compat-util.h", and they do not have to include > + "git-compat-util.h" themselves. These headers must be the first > + header file to be "#include"d in them, though. > > - A C file must directly include the header files that declare the > functions and the types it uses, except for the functions and types
Kyle Lippincott <spectral@google.com> writes: > This "In addition" ties to the "are allowed to" 19 lines below, which > was confusing for me until I intentionally ignored the "In addition", > continued reading, and finally caught the other piece of it. Perhaps > either `Exceptions:`, or something like `The following cases are > allowed to assume that their header file includes "git-compat-util.h", > and they do not have to include "git-compat-util.h" themselves:` -- I > have a slight preference for the latter form, but I worry that the > "These headers must be the first header file to be "#include"d in > them" bit will be missed. I'd appreciate people to help figuring out what the preamble should read like to make it easier to follow. > ... I don't know > if we need the reasoning why you'd #include these files in the bullets > below, which is why I didn't include it here. I'm assuming there's a > concern about implying that builtin/foo.c should include builtin.h > instead of git-compat-util.h (even if foo.c doesn't use cmd_foo()?). It is more about helping folks new to the codebase understand the reasoning behind the convention. As whoever implements "git foo" as a built-in command is supposed to - declare cmd_foo() in builtin.h - add builtin/foo.c, define cmd_foo() there, and include builtin.h - add "foo" and "cmd_foo" to git.c:commands[]. it is natural to expect any and all builtin/foo.c to include builtin.h (hence it makes it convenient to allow an exception by including compat-util in builtin.h to give everybody in builtin/ indirect access to compat-util). But those who are not yet familar with the structure of the system may not understand why it is natural. So, addition of "why is this header allowed to be a substitute for which source files? Because these source files are supposed to be including that header anyway" is an important part of this patch. Thanks.
diff --git c/Documentation/CodingGuidelines w/Documentation/CodingGuidelines index 578587a471..b3443dd773 100644 --- c/Documentation/CodingGuidelines +++ w/Documentation/CodingGuidelines @@ -446,12 +446,30 @@ For C programs: detail. - The first #include in C files, except in platform specific compat/ - implementations and sha1dc/, must be either "git-compat-util.h" or - one of the approved headers that includes it first for you. (The - approved headers currently include "builtin.h", - "t/helper/test-tool.h", "xdiff/xinclude.h", or - "reftable/system.h".) You do not have to include more than one of - these. + implementations and sha1dc/, must be "git-compat-util.h". In + addition: + + - the implementation of the built-in commands in the "builtin/" + directory that include "builtin.h" for the cmd_foo() prototype + definition + + - the test helper programs in the "t/helper/" directory that include + "t/helper/test-tool.h" for the cmd__foo() prototype definition + + - the xdiff implementation in the "xdiff/" directory that includes + "xdiff/xinclude.h" for the xdiff machinery internals + + - the unit test programs in "t/unit-tests/" directory that include + "test-lib.h" that gives them the unit-tests framework + + - the source files that implement reftable in the "reftable/" + directory that include "reftable/system.h" for the reftable + internals + + are allowed to assume that their header file includes + "git-compat-util.h", and they do not have to include + "git-compat-util.h" themselves. These headers must be the first + header file to be "#include"d in them, though. - A C file must directly include the header files that declare the functions and the types it uses, except for the functions and types
The reason why we insist including the compat-util header as the very first thing is because it is our mechanism to absorb the differences across platforms, like the order in which system header files must be included, and C preprocessor feature macros that are needed to trigger certain features we want out of the systems, and insulate other headers and sources from such minutiae. Earlier we tried to clarify the rule in the coding guidelines document, but the wording was a bit fuzzy that can lead to misinterpretations like you can include xdiff/xinclude.h only to avoid having to include git-compat-util.h file even if you have nothing to do with xdiff implementation, for example. "You do not have to include more than one of these" were also misleading and would have been puzzling if you _needed_ to depend on more than one of these approved headers (answer: you are allowed to include them all if you need the declarations in them for reasons other than that you want to avoid including compat-util yourself). Instead of using the phrase "approved headers", enumerate them as exceptions, each labeled with intended audiences, to avoid such misinterpretations. The structure also makes it easier to add new exceptions, so add the description of "t/unit-tests/test-lib.h" being an exception only for the unit tests implementation as an example. Signed-off-by: Junio C Hamano <gitster@pobox.com> --- * git-std-lib folks CC'ed to show them where to put their exception when things start to stabilize; Elijah CC'ed for his 8bff5ca0 (treewide: ensure one of the appropriate headers is sourced first, 2023-02-24) and bc5c5ec0 (cache.h: remove this no-longer-used header, 2023-05-16). Documentation/CodingGuidelines | 30 ++++++++++++++++++++++++------ 1 file changed, 24 insertions(+), 6 deletions(-)