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>

Source/cmLocalGenerator.cxx

@@ -488,16 +488,6 @@ private:
 cmGeneratorTarget* cmLocalGenerator::FindGeneratorTarget(
     const std::string& name) const
 {
-  std::map<std::string, std::string>::const_iterator i =
-      this->AliasTargets.find(name);
-  if (i != this->AliasTargets.end())
-    {
-    std::vector<cmGeneratorTarget*>::const_iterator ai =
-        std::find_if(this->GeneratorTargets.begin(),
-                     this->GeneratorTargets.end(),
-                     NamedGeneratorTargetFinder(i->second));
-    return *ai;
-    }
   std::vector<cmGeneratorTarget*>::const_iterator ti =
       std::find_if(this->GeneratorTargets.begin(),
                    this->GeneratorTargets.end(),
@@ -506,7 +496,6 @@ cmGeneratorTarget* cmLocalGenerator::FindGeneratorTarget(
     {
     return *ti;
     }
-
   return 0;
 }
 

Source/cmMakefile.cxx

@@ -4058,25 +4058,13 @@ std::vector<std::string> cmMakefile::GetPropertyKeys() const
   return this->StateSnapshot.GetDirectory().GetPropertyKeys();
 }
 
-cmTarget* cmMakefile::FindTarget(const std::string& name,
-                                 bool excludeAliases) const
+cmTarget* cmMakefile::FindTarget(const std::string& name) const
 {
-  if (!excludeAliases)
-    {
-    std::map<std::string, std::string>::const_iterator i =
-        this->AliasTargets.find(name);
-    if (i != this->AliasTargets.end())
-      {
-      cmTargets::iterator ai = this->Targets.find(i->second);
-      return &ai->second;
-      }
-    }
   cmTargets::iterator i = this->Targets.find( name );
   if ( i != this->Targets.end() )
     {
     return &i->second;
     }
-
   return 0;
 }
 
@@ -4247,7 +4235,7 @@ cmTarget* cmMakefile::FindTargetToUse(const std::string& name,
     }
 
   // Look for a target built in this directory.
-  if(cmTarget* t = this->FindTarget(name, excludeAliases))
+  if(cmTarget* t = this->FindTarget(name))
     {
     return t;
     }

Source/cmMakefile.h

@@ -388,8 +388,7 @@ public:
     }
   std::vector<cmTarget*> GetImportedTargets() const;
 
-  cmTarget* FindTarget(const std::string& name,
-                       bool excludeAliases = false) const;
+  cmTarget* FindTarget(const std::string& name) const;
 
   /** Find a target to use in place of the given name.  The target
       returned may be imported or built within the project.  */

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)