Commit Graph

12 Commits

Author SHA1 Message Date
Brad King e15a7075b5 Add an option for explicit BYPRODUCTS of custom commands (#14963)
A common idiom in CMake-based build systems is to have custom commands
that generate files not listed explicitly as outputs so that these
files do not have to be newer than the inputs.  The file modification
times of such "byproducts" are updated only when their content changes.
Then other build rules can depend on the byproducts explicitly so that
their dependents rebuild when the content of the original byproducts
really does change.

This "undeclared byproduct" approach is necessary for Makefile, VS, and
Xcode build tools because if a byproduct were listed as an output of a
rule then the rule would always rerun when the input is newer than the
byproduct but the byproduct may never be updated.

Ninja solves this problem by offering a 'restat' feature to check
whether an output was really modified after running a rule and tracking
the fact that it is up to date separately from its timestamp.  However,
Ninja also stats all dependencies up front and will only restat files
that are listed as outputs of rules with the 'restat' option enabled.
Therefore an undeclared byproduct that does not exist at the start of
the build will be considered missing and the build will fail even if
other dependencies would cause the byproduct to be available before its
dependents build.

CMake works around this limitation by adding 'phony' build rules for
custom command dependencies in the build tree that do not have any
explicit specification of what produces them.  This is not optimal
because it prevents Ninja from reporting an error when an input to a
rule really is missing.  A better approach is to allow projects to
explicitly specify the byproducts of their custom commands so that no
phony rules are needed for them.  In order to work with the non-Ninja
generators, the byproducts must be known separately from the outputs.

Add a new "BYPRODUCTS" option to the add_custom_command and
add_custom_target commands to specify byproducts explicitly.  Teach the
Ninja generator to specify byproducts as outputs of the custom commands.
In the case of POST_BUILD, PRE_LINK, and PRE_BUILD events on targets
that link, the byproducts must be specified as outputs of the link rule
that runs the commands.  Activate 'restat' for such rules so that Ninja
knows it needs to check the byproducts, but not for link rules that have
no byproducts.
2014-11-14 16:16:00 -05:00
Peter Collingbourne fe5d6e8c0f Add USES_TERMINAL option for custom commands
Teach the add_custom_command and add_custom_target commands a new
USES_TERMINAL option.  Use it to tell the generator to give the command
direct access to the terminal if possible.
2014-11-14 11:55:09 -05:00
Brad King 0cacf73959 Help: Document add_custom_command marking outputs GENERATED 2014-11-14 10:06:55 -05:00
Brad King 1fdf4ff06a Help: Suggest in add_custom_command how to create a script (#15112) 2014-09-08 14:17:36 -04:00
Brad King 412926d03a Help: Clarify add_custom_command multiple command behavior (#15112)
Explicitly say that the commands are not composed into a stateful
script.
2014-09-02 15:13:50 -04:00
Brad King 5bf1c5cce1 Help: Document add_custom_command PRE_BUILD/PRE_LINK for exe/lib only (#15059)
State explicitly that the PRE_LINK mode is not for targets created by
the add_custom_target command.  The existing wording for PRE_BUILD being
treated as PRE_LINK by non-VS generators will now imply this restriction
for PRE_BUILD too.
2014-08-05 10:14:35 -04:00
Brad King 2a58c872d7 Help: Revise and format 'add_custom_command' docs
Format the reStructuredText markup manually.  Organize the command
options into a definition list.  Use inline markup to cross-reference
related documents.
2014-08-05 10:12:59 -04:00
Brad King cb88742da4 Help: Remove stray content from 'add_custom_command' docs
Remove leftover generator expression documentation that is now in
the cmake-generator-expressions(7) manual.
2014-08-05 09:59:10 -04:00
Stephen Kelly bbffccca42 add_custom_command: Evaluate generator expressions in DEPENDS
Rely on evaluation in cmCustomCommandGenerator for the generators.

When tracing target dependencies, depend on the union of dependencies
for all configurations.
2014-03-20 09:21:56 -04:00
Stephen Kelly 85a4fad78c Help: Use ``inline-literals`` to mark generator expressions. 2014-02-06 16:15:52 -05:00
Brad King e7ca48f226 Help: Factor out cmake-generator-expressions manual page
Generator expressions are supported in many places and are a distinct
concept worthy of their own manual page.  The old builtin documentation
was previously represented by preprocessor macros to generate it into
each place that supports them.  Factor out the duplicate content into a
dedicated cmake-generator-expressions manual page and reference it from
each original location.
2013-10-16 09:22:38 -04:00
Kitware Robot f051814ed0 Convert builtin help to reStructuredText source files
Run the convert-help.bash script to convert documentation:

 ./convert-help.bash "/path/to/CMake-build/bin"

Then remove it.
2013-10-15 14:12:03 -04:00