The external project's build process may generate byproducts on which
other rules in the driving project's build later depend. Provide a way
for the driving project to specify what byproducts it expects to be made
available by the custom commands that drive the external project.
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.
Use an explicit "$TARGET_FILE" variable instead of "$out" so that
we can have multiple output files while still only referencing the
main one in command lines.
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.
Format the reStructuredText markup manually. Organize the command
options into a definition list. Use inline markup to cross-reference
related documents.
32b91b9e Features: Run GNU feature tests with std=c++14 when available.
82c283f9 Features: Use the correct dialect flag when recording features.
b18155b7 Features: Reorder the GNU C dialect feature tests
e68d5c60 Features: Split the Clang testable features to a separate file.
1abd7cd9 Use containers of labeled search paths instead of individual members
2a9ac4bd Encapsulate search path manipulation functions into a seperate class.
32922840 Refactor and seperate search path construction for find commands
3c497f11 Help: Add notes for topic 'ExternalProject_UPDATE_DISCONNECTED'
aba5cec6 ExternalProject: Add unit tests for UPDATE_DISCONNECTED
3f606fa7 ExternalProject: Add UPDATE_DISCONNECTED option
c0b749cf ExternalProject: Always add a command to a step
The CPackComponentsForAll-*, GeneratorExpression, and
TestsWorkingDirectory tests all build binaries that they later
need to run or package for the tested configuration. Tell the
'ctest --build-and-test' call to use the same configuration
for driving the build process.
The special case added by commit v2.4.0~3051 (When building CMake
itself, use the new cmake to install so that the current cmake can be
overwritten, 2004-06-09) does not make sense when cross-compiling.
Features are currently recorded accidentally for all versions of
AppleClang > 3.4 (I have no idea how that relates to upstream
Clang). Presumably that version has the features which are
accidentally recorded, but in the future features will be
recorded initially for only AppleClang >= 5.1, which would
appear as a feature regression.
Commit v3.1.0-rc1~635^2~11 (Don't load Clang-CXX from
AppleClang-CXX., 2013-11-11) ajusted the logic for the CXX
language. Make a similar change for the C language.
The evaluation files must be known before cmTargetTraceDependencies
attempts to find them, but we must actually generate the files after
cmTargetTraceDependencies, as that can add to target SOURCES. The
limitation is that the generated output name must not depend on the
SOURCES of a target if the generated file is used by that target.
Mark the output files as GENERATED so that trace dependencies does
not expect them to already exist in the filesystem.
Move the invokation of ForceLinkerLanguage in the Generate logic
to after the generated file names are known. ForceLinkerLanguage
tries to determine the sources of a target (in order to determine
an already-known language) and otherwise fails to get information
about the generated file.
Test that the output of file(GENERATE) can be used as a target source
file and that accessing the target SOURCES in the name of the output
file is an error. Accessing the TARGET_OBJECTS would be a similar
error if it was legal to use that generator expression in this
context. That is not currently possible and is a different error
condition, so test the current error output as a reminder to change
the expected output if that becomes possible in the future. Test
that generated rule files resulting from cmTargetTraceDependencies
appear in the SOURCES generated in the output file.
Brad King
Peter Collingbourne
Kitware Robot
Dmitry Polyanitsa
Stephen Kelly