[cmake-developers] [CMake 0015614]: add_custom_target/command: Can't give Target the same name as one of the Outputs

[Mantis Bug Tracker]

The following issue has been SUBMITTED. 
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http://www.cmake.org/Bug/view.php?id=15614 
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Reported By:                FlorianM
Assigned To:                
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Project:                    CMake
Issue ID:                   15614
Category:                   CCMake
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     new
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Date Submitted:             2015-06-12 16:03 EDT
Last Modified:              2015-06-12 16:03 EDT
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Summary:                    add_custom_target/command: Can't give Target  the
same name as one of the Outputs
Description: 
Let's say you want to transfer the following makefile into a CMake equivalent:

foo_in: foo.c
    $(CC) $< -o $@

foo_out: foo_in
    post_process $< > $@   

And you don't want to add the second step as a post-build step. You still want
to be able to build foo_in or foo_out separately.


Steps to Reproduce: 
I'm using the "MSYS Makefiles" generator with the following test script:

---

cmake_minimum_required(VERSION 2.8)
project(MakeTargetTest C)

file(WRITE foo.c "#include <windows.h>\nint main() {}")
file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/post_process "echo Process something")

add_executable(foo_in foo.c)
set_target_properties(foo_in PROPERTIES SUFFIX "")

add_custom_command(
    OUTPUT foo_out 
    COMMAND post_process foo_in > foo_out
    DEPENDS foo_in
)
add_custom_target(foo_out DEPENDS foo_out)

---

$ make foo_out
Built target foo_out

---

[build.make]
...
CMakeFiles/foo_out:

foo_out: CMakeFiles/foo_out
foo_out: CMakeFiles/foo_out.dir/build.make
.PHONY : foo_out

---

If I rename the custom target to something like "foo_out_test" it works
correctly:

$ make foo_out_test
Scanning dependencies of target foo_in
[ 50%] Building C object CMakeFiles/foo_in.dir/foo.c.obj
Linking C executable foo_in.
[ 50%] Built target foo_in
[100%] Generating foo_out
[100%] Built target foo_out_test

---

[build.make]
...
CMakeFiles/foo_out_test: foo_out

foo_out: foo_in.
	$(CMAKE_COMMAND) -E cmake_progress_report CMakeFiles $(CMAKE_PROGRESS_1)
	@$(CMAKE_COMMAND) -E cmake_echo_color --switch=$(COLOR) --blue --bold
"Generating foo_out"
	post_process foo_in > foo_out

foo_out_test: CMakeFiles/foo_out_test
foo_out_test: foo_out
foo_out_test: CMakeFiles/foo_out_test.dir/build.make
.PHONY : foo_out_test


Additional Information: 
I understand that the Makefile generator could get confused by dependency that
could be a file and a target dependency, but why should this be possible for
executables and not for custom commands? And why could I not at least get a
warning or error by CMake during generation (since the rule generated is just
empty, see "Steps to Reproduce")?

I can see 3 possible solutions:

1. The generator detects that there is a file and a target with the same name
and does add a suffix or prefix to its internal build rules for that file.

2. The add_custom_target() command is extended to allow to define its "final"
output which is then handled the same way a and add_executable() command output
file. 

3. Add an GENERIC (linker) language. So you could use files with any extensions
with add_executable() that are directly given to a definable "linker".

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Issue History 
Date Modified    Username       Field                    Change               
====================================================================== 
2015-06-12 16:03 FlorianM       New Issue                                    
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