Add the ALIAS target concept for libraries and executables.

* The ALIAS name must match a validity regex.
* Executables and libraries may be aliased.
* An ALIAS acts immutable. It can not be used as the lhs
  of target_link_libraries or other commands.
* An ALIAS can be used with add_custom_command, add_custom_target,
  and add_test in the same way regular targets can.
* The target of an ALIAS can be retrieved with the ALIASED_TARGET
  target property.
* An ALIAS does not appear in the generated buildsystem. It
  is kept separate from cmMakefile::Targets for that reason.
* A target may have multiple aliases.
* An ALIAS target may not itself have an alias.
* An IMPORTED target may not have an alias.
* An ALIAS may not be exported or imported.

1 files changed, 13 insertions, 0 deletions

diff --git a/Source/cmAddLibraryCommand.h b/Source/cmAddLibraryCommand.h
index e5f27cb..59354b0 100644
--- a/Source/cmAddLibraryCommand.h
+++ b/Source/cmAddLibraryCommand.h
@@ -138,6 +138,19 @@ public:
       "Some native build systems may not like targets that have only "
       "object files, so consider adding at least one real source file "
       "to any target that references $<TARGET_OBJECTS:objlib>."
+      "\n"
+      "The signature\n"
+      "  add_library(<name> ALIAS <target>)\n"
+      "creates an alias, such that <name> can be used to refer to <target> "
+      "in subsequent commands.  The <name> does not appear in the generated "
+      "buildsystem as a make target.  The <target> may not be an IMPORTED "
+      "target or an ALIAS.  Alias targets can be used as linkable targets, "
+      "targets to read properties from.  They can also be tested for "
+      "existance with the "
+      "regular if(TARGET) subcommand.  The <name> may not be used to modify "
+      "properties of <target>, that is, it may not be used as the operand of "
+      "set_property, set_target_properties, target_link_libraries etc.  An "
+      "ALIAS target may not be installed of exported."
       ;
     }