Each source compilation generates a dependencies file. These dependencies
files are consolidated in one file per target. This consolidation is done
as part of command 'cmake -E cmake_depends` launched before evaluation of
makefile dependency graph.
The consolidation uses the same approach as `CMake` dependencies management.
Fixes: #21321
Do not attach a custom command to a target if it is already attached to one of
the target's dependencies. The command's output will be available by the time
the target needs it because the dependency containing the command will have
already been built.
This may break existing projects that do not properly mark non-created
outputs with the `SYMBOLIC` property. Previously a chain of two custom
commands whose intermediate dependency is not created would put both
commands in a dependent project's Makefile even if the first command is
also in its dependency's Makefile. The first command would run twice
but the build would work. Now the second command needs an explicit
`SYMBOLIC` mark on its input to tell CMake that it is not expected to
exist. To maintain compatibility with projects that left out the mark,
add a policy activating the behavior.
Refactoring in commit v3.4.0-rc1~321^2 (cmMakefile: Remove special
handling of INCLUDE_REGULAR_EXPRESSION, 2015-04-04) accidentally broke
propagation of the include regex to subdirectories. Refactoring in
commit v3.5.0-rc1~319^2~1 (cmState: Initialize properties immediately,
2015-10-07) moved maintenance of this value from `cmMakefile` to
`cmStateSnapshot`.
Restore propagation of the `INCLUDE_REGULAR_EXPRESSION` to
subdirectories and add a test to cover it.
Fixes: #17676
Provide a way for custom commands to inform the ninja build tool about
their implicit dependencies. For now simply make use of the option an
error on other generators.
Closes: #15479
