On 2009-09-07 08:43-0400 Brad King wrote:
I know however that my proposal does not solve the other problem
regarding ignoring "<path-to-existing-build>" raised in this thread.
That use case will not be dropped. I think the two-path auto-magic
command line interpretation approach will work well if implemented
correctly, and will happily review a patch. However, see my other
suggestion below.
In the current one arg cmake invocation we should have a way to
detect/avoid an unvoluntary in-source build.
Currently we cannot.
This is the key idea. I've thought about possible solutions to this
in the past but never found time to implement any. My idea is to
have an optional "InSource.cmake" file written by the project in the
source tree. If CMake sees an attempt to build in-source, it can
load this file before touching the source tree at all. The file
could do one of the following:
1.) Simply error-out and tell the user to build out-of-source.
The source tree will remain clean.
2.) Compute the path to a build tree for CMake to auto-magically
substitute for an in-source build. Likely it would be just
"<source-tree>/build" or some convention the project prefers.
3.) Other ideas?
One gotcha with action #2 is that CMake knows nothing about the
target platform at the point the file is loaded, so projects
would be unable to compute a path like "build-x86_64".
Projects can obviously do (1) already by the appropriate IF(CMAKE_BINARY_DIR
STREQUAL "${CMAKE_SOURCE_DIR}") logic. However, I suspect most projects
prefer to give their users the flexibility to choose in-source builds.
Instead of (2) which requires users of a particular project that adopts it
to never have access to in-source builds, I far prefer the idea of giving
build systems access to the path where cmake was invoked as a CMake variable
(say CMAKE_INVOCATION_DIR). That allows projects to demand (if they like) to
error out IF(NOT CMAKE_BINARY_DIR STREQUAL "${CMAKE_INVOCATION_DIR}" AND
CMAKE_BINARY_DIR STREQUAL "${CMAKE_SOURCE_DIR}") which would disallow _just_
the problematic case where users try an in-source build, then attempt to
invoke cmake from a different location other than the top of the existing
build == source tree.
Alan
That would allow users to use
"cmake ."
or to error out when users
are attempting to follow an in-source build with a possible out-of-source
build.
detect the problematic case
(invocation path != build-tree path AND build-tree path == source-tree path)
where an attempt is made to do an in-source build from some other location
using the <path-to-existing-build> interpretation. It's this problematic
case (which can only occur if there is an in-source build followed by an
out-of-source build attempt) that I believe most projects want to avoid
rather than precluding in-source builds altogether as in (1).
Alan
__________________________
Alan W. Irwin
Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).
Programming affiliations with the FreeEOS equation-of-state implementation
for stellar interiors (freeeos.sf.net); PLplot scientific plotting software
package (plplot.org); the libLASi project (unifont.org/lasi); the Loads of
Linux Links project (loll.sf.net); and the Linux Brochure Project
(lbproject.sf.net).
__________________________
Linux-powered Science
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