add_library: Allow arbitrary non-linked sources in OBJECT libraries

Loosen this restriction on OBJECT libraries to allow source files of any
name to be generated by custom commands or listed for reference in IDE
projects so long as they would not affect linking of a normal library.
Update the rejection message to be more specific about the looser
restriction.

Extend the ObjectLibrary test to cover a ".cmake" file generated by a
custom command in an OBJECT library.

7 files changed, 27 insertions, 9 deletions

diff --git a/Help/command/add_library.rst b/Help/command/add_library.rst
index f19b5c042a..f86f3c5ec3 100644
--- a/Help/command/add_library.rst
+++ b/Help/command/add_library.rst
@@ -94,7 +94,8 @@ object library name.  For example:
 
 will include objlib's object files in a library and an executable
 along with those compiled from their own sources.  Object libraries
-may contain only sources (and headers) that compile to object files.
+may contain only sources that compile, header files, and other files
+that would not affect linking of a normal library (e.g. ``.txt``).
 They may contain custom commands generating such sources, but not
 ``PRE_BUILD``, ``PRE_LINK``, or ``POST_BUILD`` commands.  Object libraries
 cannot be imported, exported, installed, or linked.  Some native build
diff --git a/Help/release/dev/allow-OBJECT-library-extra-sources.rst b/Help/release/dev/allow-OBJECT-library-extra-sources.rst
new file mode 100644
index 0000000000..472fcdc50a
--- /dev/null
+++ b/Help/release/dev/allow-OBJECT-library-extra-sources.rst
@@ -0,0 +1,6 @@
+allow-OBJECT-library-extra-sources
+----------------------------------
+
+* :ref:`Object Libraries` may now have extra sources that do not
+  compile to object files so long as they would not affect linking
+  of a normal library (e.g. ``.dat`` is okay but not ``.def``).
diff --git a/Source/cmGeneratorTarget.cxx b/Source/cmGeneratorTarget.cxx
index eccb06adab..64c5822f8c 100644
--- a/Source/cmGeneratorTarget.cxx
+++ b/Source/cmGeneratorTarget.cxx
@@ -38,7 +38,8 @@ void reportBadObjLib(std::vector<cmSourceFile*> const& badObjLib,
       {
       e << "  " << (*i)->GetLocation().GetName() << "\n";
       }
-    e << "but may contain only headers and sources that compile.";
+    e << "but may contain only sources that compile, header files, and "
+         "other files that would not affect linking of a normal library.";
     cm->IssueMessage(cmake::FATAL_ERROR, e.str(),
                      target->GetBacktrace());
     }
@@ -205,10 +206,6 @@ struct TagVisitor
     else
       {
       DoAccept<IsSameTag<Tag, ExtraSourcesTag>::Result>::Do(this->Data, sf);
-      if(this->IsObjLib && ext != "txt")
-        {
-        this->BadObjLibFiles.push_back(sf);
-        }
       }
   }
 };
diff --git a/Tests/ObjectLibrary/A/CMakeLists.txt b/Tests/ObjectLibrary/A/CMakeLists.txt
index 3fba9f8167..c24c5ed92e 100644
--- a/Tests/ObjectLibrary/A/CMakeLists.txt
+++ b/Tests/ObjectLibrary/A/CMakeLists.txt
@@ -11,5 +11,16 @@ add_custom_command(
                                    ${CMAKE_CURRENT_BINARY_DIR}/a1.c
   )
 
-add_library(A OBJECT a1.c a2.c)
+# Remove the custom command output to be sure it runs in an
+# incremental test.  Skip this on VS 6 because it sometimes
+# re-runs CMake after the custom command runs.
+if(NOT CMAKE_GENERATOR STREQUAL "Visual Studio 6")
+  file(REMOVE ${CMAKE_CURRENT_BINARY_DIR}/a.cmake)
+endif()
+add_custom_command(
+  OUTPUT a.cmake
+  COMMAND ${CMAKE_COMMAND} -E touch ${CMAKE_CURRENT_BINARY_DIR}/a.cmake
+  )
+
+add_library(A OBJECT a1.c a2.c a.cmake)
 target_include_directories(A PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
diff --git a/Tests/ObjectLibrary/CMakeLists.txt b/Tests/ObjectLibrary/CMakeLists.txt
index 75c34d8252..e9f553e2be 100644
--- a/Tests/ObjectLibrary/CMakeLists.txt
+++ b/Tests/ObjectLibrary/CMakeLists.txt
@@ -12,6 +12,7 @@ add_library(Cshared SHARED c.c $<TARGET_OBJECTS:A> $<TARGET_OBJECTS:Bexport>)
 add_executable(UseCshared main.c)
 set_property(TARGET UseCshared PROPERTY COMPILE_DEFINITIONS SHARED_C)
 target_link_libraries(UseCshared Cshared)
+add_custom_command(TARGET UseCshared POST_BUILD COMMAND ${CMAKE_COMMAND} -P ${CMAKE_CURRENT_BINARY_DIR}/A/a.cmake)
 
 add_executable(UseCinternal main.c c.c $<TARGET_OBJECTS:A> $<TARGET_OBJECTS:B>)
 
diff --git a/Tests/RunCMake/ObjectLibrary/BadObjSource1-stderr.txt b/Tests/RunCMake/ObjectLibrary/BadObjSource1-stderr.txt
index b31225b488..a09552b763 100644
--- a/Tests/RunCMake/ObjectLibrary/BadObjSource1-stderr.txt
+++ b/Tests/RunCMake/ObjectLibrary/BadObjSource1-stderr.txt
@@ -3,6 +3,7 @@ CMake Error at BadObjSource1.cmake:1 \(add_library\):
 
     bad.def
 
-  but may contain only headers and sources that compile.
+  but may contain only sources that compile, header files, and other files
+  that would not affect linking of a normal library.
 Call Stack \(most recent call first\):
   CMakeLists.txt:3 \(include\)
diff --git a/Tests/RunCMake/ObjectLibrary/BadObjSource2-stderr.txt b/Tests/RunCMake/ObjectLibrary/BadObjSource2-stderr.txt
index 906cf0b642..b91ffd0682 100644
--- a/Tests/RunCMake/ObjectLibrary/BadObjSource2-stderr.txt
+++ b/Tests/RunCMake/ObjectLibrary/BadObjSource2-stderr.txt
@@ -3,6 +3,7 @@ CMake Error at BadObjSource2.cmake:1 \(add_library\):
 
     bad.obj
 
-  but may contain only headers and sources that compile.
+  but may contain only sources that compile, header files, and other files
+  that would not affect linking of a normal library.
 Call Stack \(most recent call first\):
   CMakeLists.txt:3 \(include\)