Alias: Fix access at generate-time (#15832)

Commit c389f8bb (cmLocalGenerator: Port Find method away from
GetGeneratorTarget, 2015-10-25) ported the implementation of
FindGeneratorTargetToUse away from the FindTargetToUse method,
but neglected to handle alias targets.

The latter method has a parameter to determine whether to
include alias targets in the search, but as that is only
needed at configure time, this generate-time equivalent does
not need the condition.

Source/cmGlobalGenerator.cxx

@@ -2274,6 +2274,12 @@ cmGlobalGenerator::FindTarget(const std::string& name,
 cmGeneratorTarget*
 cmGlobalGenerator::FindGeneratorTarget(const std::string& name) const
 {
+  std::map<std::string, std::string>::const_iterator ai =
+      this->AliasTargets.find(name);
+  if (ai != this->AliasTargets.end())
+    {
+    return this->FindGeneratorTargetImpl(ai->second);
+    }
   if (cmGeneratorTarget* tgt = this->FindGeneratorTargetImpl(name))
     {
     return tgt;

Tests/AliasTarget/CMakeLists.txt

@@ -37,7 +37,9 @@ target_include_directories(bat PRIVATE "${CMAKE_CURRENT_BINARY_DIR}")
 add_executable(targetgenerator targetgenerator.cpp)
 add_executable(Generator::Target ALIAS targetgenerator)
 
-add_custom_target(usealias Generator::Target)
+add_subdirectory(subdir)
+
+add_custom_target(usealias Generator::Target $<TARGET_FILE:Sub::tgt>)
 add_dependencies(bat usealias)
 
 if (NOT TARGET Another::Alias)

Tests/AliasTarget/subdir/CMakeLists.txt

@@ -0,0 +1,3 @@
+
+add_library(tgt STATIC empty.cpp)
+add_library(Sub::tgt ALIAS tgt)

Tests/AliasTarget/subdir/empty.cpp

@@ -0,0 +1,7 @@
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+int main(void)
+{
+  return 0;
+}