Fix lookup of an ALIAS target outside aliased target's directory (#16044)

Refactoring in commit v3.5.0-rc1~272^2~11 (cmTarget: Implement ALIAS in
terms of name mapping, 2015-10-25) accidentally introduced logic that
assumes ALIAS targets always reference targets in their own directory.
Fix this and add a test case.

The configure-step fix is that `cmMakefile::FindTarget` should not consider
aliases.  The purpose of this method is just to look up targets local to
a directory.  Since ALIAS and normal targets share a namespace we know a
locally defined target will never collide with an ALIAS target anyway.
The method has 3 call sites, and this change is safe for all of them:

* `cmInstallCommand::HandleTargetsMode`: Rejects aliases before the call.
* `cmFLTKWrapUICommand::FinalPass`: Should never have considered aliases.
* `cmMakefile::FindTargetToUse`: Falls back to a global lookup anyway.

The generate-step fix is that `cmLocalGenerator::FindGeneratorTarget`
should not consider aliases.  This method is the generate-step
equivalent to the above.  The method has 2 call sites, and this change
is safe for both of them:

* `cmInstallTargetGenerator::Compute`: Never uses an alias target name.
* `cmLocalGenerator::FindGeneratorTargetToUse`: Falls back to global lookup.

Reported-by: Matteo Settenvini <matteo@member.fsf.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/Tests/AliasTarget/subdir/CMakeLists.txt b/Tests/AliasTarget/subdir/CMakeLists.txt
index 8c84aea..05a7d86 100644
--- a/Tests/AliasTarget/subdir/CMakeLists.txt
+++ b/Tests/AliasTarget/subdir/CMakeLists.txt
@@ -1,3 +1,8 @@
 
 add_library(tgt STATIC empty.cpp)
 add_library(Sub::tgt ALIAS tgt)
+
+# foo comes from the top-level CMakeLists.txt
+add_library(Top::foo ALIAS foo)
+get_target_property(some_prop Top::foo SOME_PROP)
+target_link_libraries(tgt Top::foo)