Add INTERFACE libraries to generated buildsystem if they have SOURCES

INTERFACE libraries were created with the intention of collecting usage
requirements for use by other targets via `target_link_libraries`.
Therefore they were not allowed to have SOURCES and were not included in
the generated buildsystem.  In practice, this has become limiting:

* Header-only libraries do have sources, they just do not compile.
  Developers should be able to edit those sources (the header files)
  in their IDE.

* Header-only libraries may need to generate some of their header
  files via custom commands.

Some projects work around these limitations by pairing each interface
library with an `add_custom_target` that makes the header files and
custom commands appear in the generated buildsystem and in IDEs.

Lift such limitations by allowing INTERFACE libraries to have SOURCES.
For those with sources, add a corresponding build target to the
generated buildsystem.

Fixes: #19145

34 files changed, 192 insertions, 21 deletions

diff --git a/Tests/ExportImport/Export/Interface/CMakeLists.txt b/Tests/ExportImport/Export/Interface/CMakeLists.txt
index 43b7217788..ba2164bc30 100644
--- a/Tests/ExportImport/Export/Interface/CMakeLists.txt
+++ b/Tests/ExportImport/Export/Interface/CMakeLists.txt
@@ -1,11 +1,26 @@
-
-add_library(headeronly INTERFACE)
+set(headeronly_headers headeronly/headeronly.h)
+add_library(headeronly INTERFACE ${headeronly_headers})
 set_property(TARGET headeronly PROPERTY INTERFACE_INCLUDE_DIRECTORIES
   "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/headeronly>"
   "$<INSTALL_INTERFACE:${CMAKE_INSTALL_PREFIX}/include/headeronly>"
 )
 set_property(TARGET headeronly PROPERTY INTERFACE_COMPILE_DEFINITIONS "HEADERONLY_DEFINE")
 
+add_custom_command(OUTPUT headergen/headergen.h
+  COMMAND ${CMAKE_COMMAND} -E copy
+    ${CMAKE_CURRENT_SOURCE_DIR}/headergen.h.in
+    ${CMAKE_CURRENT_BINARY_DIR}/headergen/headergen.h
+  DEPENDS
+    ${CMAKE_CURRENT_SOURCE_DIR}/headergen.h.in
+  VERBATIM)
+
+add_library(headergen INTERFACE headergen/headergen.h)
+set_property(TARGET headergen PROPERTY INTERFACE_INCLUDE_DIRECTORIES
+  "$<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}/headergen>"
+)
+set_property(TARGET headergen PROPERTY PUBLIC_HEADER
+  ${CMAKE_CURRENT_BINARY_DIR}/headergen/headergen.h)
+
 add_library(pch_iface INTERFACE)
 target_precompile_headers(pch_iface INTERFACE
   "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/pch/pch.h>"
@@ -54,6 +69,11 @@ install(TARGETS headeronly sharediface use_auto_type use_c_restrict source_targe
                 pch_iface cmakeonly
   EXPORT expInterface
 )
+install(TARGETS headergen
+  EXPORT expInterface
+  PUBLIC_HEADER DESTINATION include/headergen
+  INCLUDES DESTINATION include/headergen
+)
 install(TARGETS sharedlib
   EXPORT expInterface
   RUNTIME DESTINATION bin
@@ -63,7 +83,7 @@ install(TARGETS sharedlib
   BUNDLE DESTINATION Applications
 )
 install(FILES
-  headeronly/headeronly.h
+  ${headeronly_headers}
   DESTINATION include/headeronly
 )
 install(FILES
diff --git a/Tests/ExportImport/Export/Interface/headergen.h.in b/Tests/ExportImport/Export/Interface/headergen.h.in
new file mode 100644
index 0000000000..bda2b816f4
--- /dev/null
+++ b/Tests/ExportImport/Export/Interface/headergen.h.in
@@ -0,0 +1 @@
+#define HEADERGEN_H
diff --git a/Tests/ExportImport/Import/Interface/CMakeLists.txt b/Tests/ExportImport/Import/Interface/CMakeLists.txt
index ef666b1a77..202c23e211 100644
--- a/Tests/ExportImport/Import/Interface/CMakeLists.txt
+++ b/Tests/ExportImport/Import/Interface/CMakeLists.txt
@@ -12,6 +12,9 @@ set_property(TARGET define_iface PROPERTY
 add_executable(headeronlytest_bld headeronlytest.cpp)
 target_link_libraries(headeronlytest_bld bld::headeronly)
 
+add_executable(headergentest_bld headergentest.cpp)
+target_link_libraries(headergentest_bld bld::headergen)
+
 set_property(TARGET bld::sharediface APPEND PROPERTY INTERFACE_LINK_LIBRARIES define_iface)
 
 add_executable(interfacetest_bld interfacetest.cpp)
@@ -93,6 +96,9 @@ target_compile_definitions(source_target_test_exp PRIVATE USE_FROM_INSTALL_DIR)
 add_executable(headeronlytest_exp headeronlytest.cpp)
 target_link_libraries(headeronlytest_exp exp::headeronly)
 
+add_executable(headergentest_exp headergentest.cpp)
+target_link_libraries(headergentest_exp exp::headergen)
+
 set_property(TARGET exp::sharediface APPEND PROPERTY INTERFACE_LINK_LIBRARIES define_iface)
 
 add_executable(interfacetest_exp interfacetest.cpp)
diff --git a/Tests/ExportImport/Import/Interface/headergentest.cpp b/Tests/ExportImport/Import/Interface/headergentest.cpp
new file mode 100644
index 0000000000..88ff7f1b73
--- /dev/null
+++ b/Tests/ExportImport/Import/Interface/headergentest.cpp
@@ -0,0 +1,11 @@
+
+#include "headergen.h"
+
+#ifndef HEADERGEN_H
+#  error Expected HEADERGEN_H
+#endif
+
+int main()
+{
+  return 0;
+}
diff --git a/Tests/InterfaceLibrary/CMakeLists.txt b/Tests/InterfaceLibrary/CMakeLists.txt
index 311ca2a4e7..ec0a604050 100644
--- a/Tests/InterfaceLibrary/CMakeLists.txt
+++ b/Tests/InterfaceLibrary/CMakeLists.txt
@@ -44,6 +44,7 @@ add_executable(InterfaceLibrary definetestexe.cpp)
 target_link_libraries(InterfaceLibrary
   iface_nodepends
   headeriface
+  iface_genheader
   subiface
   intermediate
 
diff --git a/Tests/InterfaceLibrary/definetestexe.cpp b/Tests/InterfaceLibrary/definetestexe.cpp
index 9156426cdb..6c538405e3 100644
--- a/Tests/InterfaceLibrary/definetestexe.cpp
+++ b/Tests/InterfaceLibrary/definetestexe.cpp
@@ -15,6 +15,12 @@
 #  error Expected IFACE_HEADER_BUILDDIR
 #endif
 
+#include "iface_genheader.h"
+
+#ifndef IFACE_GENHEADER
+#  error Expected IFACE_GENHEADER
+#endif
+
 extern int obj();
 extern int sub();
 extern int item();
diff --git a/Tests/InterfaceLibrary/headerdir/CMakeLists.txt b/Tests/InterfaceLibrary/headerdir/CMakeLists.txt
index 826a9ed9c0..ae030d7516 100644
--- a/Tests/InterfaceLibrary/headerdir/CMakeLists.txt
+++ b/Tests/InterfaceLibrary/headerdir/CMakeLists.txt
@@ -11,3 +11,12 @@ add_custom_target(headeriface_gen
   VERBATIM
   )
 add_dependencies(headeriface headeriface_gen)
+
+add_custom_command(OUTPUT iface_genheader.h
+  COMMAND ${CMAKE_COMMAND} -E copy
+    ${CMAKE_CURRENT_SOURCE_DIR}/iface_genheader.h.in
+    ${CMAKE_CURRENT_BINARY_DIR}/iface_genheader.h
+  DEPENDS
+    ${CMAKE_CURRENT_SOURCE_DIR}/iface_genheader.h.in
+  VERBATIM)
+add_library(iface_genheader INTERFACE iface_genheader.h)
diff --git a/Tests/InterfaceLibrary/headerdir/iface_genheader.h.in b/Tests/InterfaceLibrary/headerdir/iface_genheader.h.in
new file mode 100644
index 0000000000..0a21b62688
--- /dev/null
+++ b/Tests/InterfaceLibrary/headerdir/iface_genheader.h.in
@@ -0,0 +1 @@
+#define IFACE_GENHEADER
diff --git a/Tests/RunCMake/InterfaceLibrary/ConfigSources.cmake b/Tests/RunCMake/InterfaceLibrary/ConfigSources.cmake
new file mode 100644
index 0000000000..631a845587
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/ConfigSources.cmake
@@ -0,0 +1,2 @@
+# Test an interface library added to the build system by a per-config source.
+add_library(iface INTERFACE $<$<CONFIG:NotAConfig>:${CMAKE_CURRENT_SOURCE_DIR}/iface.c>)
diff --git a/Tests/RunCMake/InterfaceLibrary/EmptySources-build2-result.txt b/Tests/RunCMake/InterfaceLibrary/EmptySources-build2-result.txt
new file mode 100644
index 0000000000..d197c913c2
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/EmptySources-build2-result.txt
@@ -0,0 +1 @@
+[^0]
diff --git a/Tests/RunCMake/InterfaceLibrary/EmptySources-build2-stdout.txt b/Tests/RunCMake/InterfaceLibrary/EmptySources-build2-stdout.txt
new file mode 100644
index 0000000000..aac9172329
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/EmptySources-build2-stdout.txt
@@ -0,0 +1 @@
+iface2|Invalid project
diff --git a/Tests/RunCMake/InterfaceLibrary/EmptySources.cmake b/Tests/RunCMake/InterfaceLibrary/EmptySources.cmake
new file mode 100644
index 0000000000..f452394181
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/EmptySources.cmake
@@ -0,0 +1,8 @@
+# Test an interface library added to the build system by empty SOURCES.
+add_library(iface INTERFACE)
+set_property(TARGET iface PROPERTY SOURCES "")
+
+# ...but not added by unset SOURCES.
+add_library(iface2 INTERFACE)
+set_property(TARGET iface2 PROPERTY SOURCES "")
+set_property(TARGET iface2 PROPERTY SOURCES)
diff --git a/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll-build1-check.cmake b/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll-build1-check.cmake
new file mode 100644
index 0000000000..6500e48525
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll-build1-check.cmake
@@ -0,0 +1,4 @@
+if(EXISTS "${RunCMake_TEST_BINARY_DIR}/iface.txt")
+  set(RunCMake_TEST_FAILED "iface target built as part of 'all'")
+  return()
+endif()
diff --git a/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll-build2-check.cmake b/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll-build2-check.cmake
new file mode 100644
index 0000000000..0977c242bf
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll-build2-check.cmake
@@ -0,0 +1,4 @@
+if(NOT EXISTS "${RunCMake_TEST_BINARY_DIR}/iface.txt")
+  set(RunCMake_TEST_FAILED "iface target not built")
+  return()
+endif()
diff --git a/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll-build3-result.txt b/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll-build3-result.txt
new file mode 100644
index 0000000000..d197c913c2
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll-build3-result.txt
@@ -0,0 +1 @@
+[^0]
diff --git a/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll-build3-stdout.txt b/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll-build3-stdout.txt
new file mode 100644
index 0000000000..aac9172329
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll-build3-stdout.txt
@@ -0,0 +1 @@
+iface2|Invalid project
diff --git a/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll.cmake b/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll.cmake
new file mode 100644
index 0000000000..714161df76
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/ExcludeFromAll.cmake
@@ -0,0 +1,7 @@
+# Test an interface library with a custom command, but excluded from all.
+add_custom_command(OUTPUT iface.txt COMMAND ${CMAKE_COMMAND} -E touch iface.txt)
+add_library(iface INTERFACE EXCLUDE_FROM_ALL iface.txt)
+
+# Test that EXCLUDE_FROM_ALL is allowed even if the interface library has
+# no sources, and does not cause it to appear in the build system.
+add_library(iface2 INTERFACE EXCLUDE_FROM_ALL)
diff --git a/Tests/RunCMake/InterfaceLibrary/PublicSources-build3-result.txt b/Tests/RunCMake/InterfaceLibrary/PublicSources-build3-result.txt
new file mode 100644
index 0000000000..d197c913c2
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/PublicSources-build3-result.txt
@@ -0,0 +1 @@
+[^0]
diff --git a/Tests/RunCMake/InterfaceLibrary/PublicSources-build3-stdout.txt b/Tests/RunCMake/InterfaceLibrary/PublicSources-build3-stdout.txt
new file mode 100644
index 0000000000..aac9172329
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/PublicSources-build3-stdout.txt
@@ -0,0 +1 @@
+iface2|Invalid project
diff --git a/Tests/RunCMake/InterfaceLibrary/PublicSources.cmake b/Tests/RunCMake/InterfaceLibrary/PublicSources.cmake
new file mode 100644
index 0000000000..24785bb218
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/PublicSources.cmake
@@ -0,0 +1,20 @@
+cmake_policy(SET CMP0076 NEW)
+enable_language(C)
+
+# Test that an interface library can have PUBLIC sources.
+# This causes the target to appear in the build system
+# *and* causes consumers to use the source.
+add_library(iface INTERFACE)
+target_sources(iface
+  PUBLIC iface.c
+  # Private sources do not compile here or propagate.
+  PRIVATE iface_broken.c
+  )
+
+# Test that an intermediate interface library does not get the
+# sources and does not appear in the build system.
+add_library(iface2 INTERFACE)
+target_link_libraries(iface2 INTERFACE iface)
+
+add_executable(use_iface use_iface.c)
+target_link_libraries(use_iface PRIVATE iface2)
diff --git a/Tests/RunCMake/InterfaceLibrary/RunCMakeTest.cmake b/Tests/RunCMake/InterfaceLibrary/RunCMakeTest.cmake
index b84bc33a07..834b3c8fe5 100644
--- a/Tests/RunCMake/InterfaceLibrary/RunCMakeTest.cmake
+++ b/Tests/RunCMake/InterfaceLibrary/RunCMakeTest.cmake
@@ -10,3 +10,27 @@ run_cmake(add_custom_command-TARGET)
 run_cmake(IMPORTED_LIBNAME-bad-value)
 run_cmake(IMPORTED_LIBNAME-non-iface)
 run_cmake(IMPORTED_LIBNAME-non-imported)
+
+function(run_WithSources CASE)
+  if(NOT RunCMake_GENERATOR_IS_MULTI_CONFIG)
+    set(RunCMake_TEST_OPTIONS -DCMAKE_BUILD_TYPE=Debug)
+  endif()
+  set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/${CASE}-build)
+  run_cmake(${CASE})
+  set(RunCMake_TEST_NO_CLEAN 1)
+  foreach(build IN LISTS ARGN)
+    if(build MATCHES "^([^:]+)$")
+      run_cmake_command(${CASE}-${CMAKE_MATCH_1} ${CMAKE_COMMAND} --build . --config Debug)
+    elseif(build MATCHES "^([^:]+):([^:,]+)(,merge)?$")
+      if(CMAKE_MATCH_3 STREQUAL ",merge")
+        set(RunCMake_TEST_OUTPUT_MERGE 1)
+      endif()
+      run_cmake_command(${CASE}-${CMAKE_MATCH_1} ${CMAKE_COMMAND} --build . --config Debug --target ${CMAKE_MATCH_2})
+    endif()
+  endforeach()
+endfunction()
+
+run_WithSources(ConfigSources "build1:iface")
+run_WithSources(EmptySources "build1:iface" "build2:iface2,merge")
+run_WithSources(ExcludeFromAll "build1" "build2:iface" "build3:iface2,merge")
+run_WithSources(PublicSources "build1" "build2:iface" "build3:iface2,merge")
diff --git a/Tests/RunCMake/InterfaceLibrary/iface.c b/Tests/RunCMake/InterfaceLibrary/iface.c
new file mode 100644
index 0000000000..c7e7372ef3
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/iface.c
@@ -0,0 +1,4 @@
+int iface(void)
+{
+  return 0;
+}
diff --git a/Tests/RunCMake/InterfaceLibrary/iface_broken.c b/Tests/RunCMake/InterfaceLibrary/iface_broken.c
new file mode 100644
index 0000000000..4ff7f31919
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/iface_broken.c
@@ -0,0 +1 @@
+#error This file should not compile
diff --git a/Tests/RunCMake/InterfaceLibrary/invalid_signature-stderr.txt b/Tests/RunCMake/InterfaceLibrary/invalid_signature-stderr.txt
index 6374b3392b..763f9f8e2f 100644
--- a/Tests/RunCMake/InterfaceLibrary/invalid_signature-stderr.txt
+++ b/Tests/RunCMake/InterfaceLibrary/invalid_signature-stderr.txt
@@ -1,8 +1,3 @@
-CMake Error at invalid_signature.cmake:2 \(add_library\):
-  add_library INTERFACE library requires no source arguments.
-Call Stack \(most recent call first\):
-  CMakeLists.txt:3 \(include\)
-+
 CMake Error at invalid_signature.cmake:3 \(add_library\):
   add_library INTERFACE library specified with conflicting/multiple types.
 Call Stack \(most recent call first\):
@@ -73,16 +68,6 @@ CMake Error at invalid_signature.cmake:16 \(add_library\):
 Call Stack \(most recent call first\):
   CMakeLists.txt:3 \(include\)
 +
-CMake Error at invalid_signature.cmake:17 \(add_library\):
-  add_library INTERFACE library may not be used with EXCLUDE_FROM_ALL.
-Call Stack \(most recent call first\):
-  CMakeLists.txt:3 \(include\)
-+
-CMake Error at invalid_signature.cmake:18 \(add_library\):
-  add_library INTERFACE library may not be used with EXCLUDE_FROM_ALL.
-Call Stack \(most recent call first\):
-  CMakeLists.txt:3 \(include\)
-+
 CMake Error at invalid_signature.cmake:20 \(add_library\):
   add_library GLOBAL option may only be used with IMPORTED libraries.
 Call Stack \(most recent call first\):
diff --git a/Tests/RunCMake/InterfaceLibrary/invalid_signature.cmake b/Tests/RunCMake/InterfaceLibrary/invalid_signature.cmake
index 4e53534b28..2a575b5047 100644
--- a/Tests/RunCMake/InterfaceLibrary/invalid_signature.cmake
+++ b/Tests/RunCMake/InterfaceLibrary/invalid_signature.cmake
@@ -1,5 +1,5 @@
 
-add_library(iface1 INTERFACE empty.cpp)
+
 add_library(iface3 STATIC INTERFACE)
 add_library(iface4 STATIC INTERFACE empty.cpp)
 add_library(iface5 SHARED INTERFACE)
@@ -14,7 +14,7 @@ add_library(iface13 INTERFACE UNKNOWN)
 add_library(iface14 INTERFACE ALIAS)
 add_library(iface15 ALIAS INTERFACE)
 add_library(iface16 INTERFACE INTERFACE)
-add_library(iface17 INTERFACE EXCLUDE_FROM_ALL)
-add_library(iface18 EXCLUDE_FROM_ALL INTERFACE)
+
+
 # add_library(iface19 GLOBAL INTERFACE) Tested separately
 add_library(iface20 INTERFACE GLOBAL)
diff --git a/Tests/RunCMake/InterfaceLibrary/use_iface.c b/Tests/RunCMake/InterfaceLibrary/use_iface.c
new file mode 100644
index 0000000000..66293e4615
--- /dev/null
+++ b/Tests/RunCMake/InterfaceLibrary/use_iface.c
@@ -0,0 +1,6 @@
+extern int iface(void);
+
+int main(void)
+{
+  return iface();
+}
diff --git a/Tests/RunCMake/VS10Project/InterfaceLibSources-check.cmake b/Tests/RunCMake/VS10Project/InterfaceLibSources-check.cmake
new file mode 100644
index 0000000000..bcdc10105d
--- /dev/null
+++ b/Tests/RunCMake/VS10Project/InterfaceLibSources-check.cmake
@@ -0,0 +1,25 @@
+set(vcProjectFile "${RunCMake_TEST_BINARY_DIR}/iface.vcxproj")
+if(NOT EXISTS "${vcProjectFile}")
+  set(RunCMake_TEST_FAILED "Project file ${vcProjectFile} does not exist.")
+  return()
+endif()
+
+set(found_iface_h 0)
+file(STRINGS "${vcProjectFile}" lines)
+foreach(line IN LISTS lines)
+  if(line MATCHES "<([A-Za-z0-9_]+) +Include=.*iface\\.h")
+    set(rule "${CMAKE_MATCH_1}")
+    if(NOT rule STREQUAL "None")
+      set(RunCMake_TEST_FAILED "iface.h referenced as ${rule} instead of None in\n  ${vcProjectFile}")
+      return()
+    endif()
+    if(found_iface_h)
+      set(RunCMake_TEST_FAILED "iface.h referenced multiple times in\n  ${vcProjectFile}")
+      return()
+    endif()
+    set(found_iface_h 1)
+  endif()
+endforeach()
+if(NOT found_iface_h)
+  set(RunCMake_TEST_FAILED "iface.h not referenced in\n  ${vcProjectFile}")
+endif()
diff --git a/Tests/RunCMake/VS10Project/InterfaceLibSources.cmake b/Tests/RunCMake/VS10Project/InterfaceLibSources.cmake
new file mode 100644
index 0000000000..3672be18c0
--- /dev/null
+++ b/Tests/RunCMake/VS10Project/InterfaceLibSources.cmake
@@ -0,0 +1 @@
+add_library(iface INTERFACE iface.h)
diff --git a/Tests/RunCMake/VS10Project/RunCMakeTest.cmake b/Tests/RunCMake/VS10Project/RunCMakeTest.cmake
index 93ef60343b..e9f251ab3c 100644
--- a/Tests/RunCMake/VS10Project/RunCMakeTest.cmake
+++ b/Tests/RunCMake/VS10Project/RunCMakeTest.cmake
@@ -6,6 +6,7 @@ cmake_policy(SET CMP0054 NEW)
 run_cmake(VsCsharpSourceGroup)
 run_cmake(VsCSharpCompilerOpts)
 run_cmake(ExplicitCMakeLists)
+run_cmake(InterfaceLibSources)
 run_cmake(RuntimeLibrary)
 run_cmake(SourceGroupCMakeLists)
 run_cmake(SourceGroupTreeCMakeLists)
diff --git a/Tests/RunCMake/VS10Project/iface.h b/Tests/RunCMake/VS10Project/iface.h
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/Tests/RunCMake/VS10Project/iface.h
diff --git a/Tests/RunCMake/XcodeProject/InterfaceLibSources-check.cmake b/Tests/RunCMake/XcodeProject/InterfaceLibSources-check.cmake
new file mode 100644
index 0000000000..613951a465
--- /dev/null
+++ b/Tests/RunCMake/XcodeProject/InterfaceLibSources-check.cmake
@@ -0,0 +1,16 @@
+set(xcProjectFile "${RunCMake_TEST_BINARY_DIR}/InterfaceLibSources.xcodeproj/project.pbxproj")
+if(NOT EXISTS "${xcProjectFile}")
+  set(RunCMake_TEST_FAILED "Project file ${xcProjectFile} does not exist.")
+  return()
+endif()
+
+set(found_iface_h 0)
+file(STRINGS "${xcProjectFile}" lines)
+foreach(line IN LISTS lines)
+  if(line MATCHES "PBXFileReference.*explicitFileType.*sourcecode\\.c\\.h.*iface\\.h")
+    set(found_iface_h 1)
+  endif()
+endforeach()
+if(NOT found_iface_h)
+  set(RunCMake_TEST_FAILED "iface.h not referenced in\n  ${xcProjectFile}")
+endif()
diff --git a/Tests/RunCMake/XcodeProject/InterfaceLibSources.cmake b/Tests/RunCMake/XcodeProject/InterfaceLibSources.cmake
new file mode 100644
index 0000000000..3672be18c0
--- /dev/null
+++ b/Tests/RunCMake/XcodeProject/InterfaceLibSources.cmake
@@ -0,0 +1 @@
+add_library(iface INTERFACE iface.h)
diff --git a/Tests/RunCMake/XcodeProject/RunCMakeTest.cmake b/Tests/RunCMake/XcodeProject/RunCMakeTest.cmake
index 342dbbcdcc..cd6fd06d58 100644
--- a/Tests/RunCMake/XcodeProject/RunCMakeTest.cmake
+++ b/Tests/RunCMake/XcodeProject/RunCMakeTest.cmake
@@ -2,6 +2,7 @@ include(RunCMake)
 
 run_cmake(ExplicitCMakeLists)
 run_cmake(ImplicitCMakeLists)
+run_cmake(InterfaceLibSources)
 
 run_cmake(XcodeFileType)
 run_cmake(XcodeAttributeLocation)
diff --git a/Tests/RunCMake/XcodeProject/iface.h b/Tests/RunCMake/XcodeProject/iface.h
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/Tests/RunCMake/XcodeProject/iface.h