ExternalData: Allow local stores without any URL templates

Allow ExternalData_URL_TEMPLATES to be empty if a value for
ExternalData_OBJECT_STORES is provided.  Assume in this use case that
the object stores will already contain all needed objects.  Extend the
Module.ExternalData test to cover this case (all objects in stores).
Extend the RunCMake.ExternalData test to cover the non-failure message
case when stores are provided without URL templates.

Modules/ExternalData.cmake

@@ -58,7 +58,7 @@
 #
 # It creates custom commands in the target as necessary to make data
 # files available for each ``DATA{}`` reference previously evaluated by
-# other functions provided by this module.  A list of URL templates must
+# other functions provided by this module.  A list of URL templates may
 # be provided in the variable ``ExternalData_URL_TEMPLATES`` using the
 # placeholders ``%(algo)`` and ``%(hash)`` in each template.  Data fetch
 # rules try each URL template in order by substituting the hash
@@ -202,8 +202,9 @@ function(ExternalData_add_test target)
 endfunction()
 
 function(ExternalData_add_target target)
-  if(NOT ExternalData_URL_TEMPLATES)
-    message(FATAL_ERROR "ExternalData_URL_TEMPLATES is not set!")
+  if(NOT ExternalData_URL_TEMPLATES AND NOT ExternalData_OBJECT_STORES)
+    message(FATAL_ERROR
+      "Neither ExternalData_URL_TEMPLATES nor ExternalData_OBJECT_STORES is set!")
   endif()
   if(NOT ExternalData_OBJECT_STORES)
     set(ExternalData_OBJECT_STORES ${CMAKE_BINARY_DIR}/ExternalData/Objects)
@@ -625,8 +626,9 @@ endif()
 if(ExternalData_CONFIG)
   include(${ExternalData_CONFIG})
 endif()
-if(NOT ExternalData_URL_TEMPLATES)
-  message(FATAL_ERROR "No ExternalData_URL_TEMPLATES set!")
+if(NOT ExternalData_URL_TEMPLATES AND NOT ExternalData_OBJECT_STORES)
+  message(FATAL_ERROR
+    "Neither ExternalData_URL_TEMPLATES nor ExternalData_OBJECT_STORES is set!")
 endif()
 
 function(_ExternalData_link_or_copy src dst)
@@ -754,6 +756,9 @@ function(_ExternalData_download_object name hash algo var_obj)
     set(obj "${staged}")
     message(STATUS "Staged object: \"${obj}\"")
   else()
+    if(NOT tried)
+      set(tried "\n  (No ExternalData_URL_TEMPLATES given)")
+    endif()
     message(FATAL_ERROR "Object ${algo}=${hash} not found at:${tried}")
   endif()
 

Tests/Module/ExternalData/CMakeLists.txt

@@ -42,3 +42,4 @@ ExternalData_Add_Target(Data1)
 
 add_subdirectory(Data2)
 add_subdirectory(Data3)
+add_subdirectory(Data4)

Tests/Module/ExternalData/Data4/CMakeLists.txt

@@ -0,0 +1,15 @@
+set(Store0 ${CMAKE_BINARY_DIR}/ExternalData/Other)
+set(Store1 ${CMAKE_BINARY_DIR}/ExternalData/Objects)
+set(ExternalData_OBJECT_STORES ${Store0} ${Store1})
+unset(ExternalData_URL_TEMPLATES) # All objects already in stores!
+ExternalData_Add_Test(Data4
+  NAME Data4Check
+  COMMAND ${CMAKE_COMMAND}
+    -D Data=DATA{Data.dat}
+    -D Other=DATA{Other.dat}
+    -D Store0=${Store0}
+    -D Store1=${Store1}
+    -P ${CMAKE_CURRENT_SOURCE_DIR}/Data4Check.cmake
+  )
+ExternalData_Add_Target(Data4)
+add_dependencies(Data4 Data3)

Tests/Module/ExternalData/Data4/Data.dat.md5

@@ -0,0 +1 @@
+8c018830e3efa5caf3c7415028335a57

Tests/Module/ExternalData/Data4/Data4Check.cmake

@@ -0,0 +1,26 @@
+if(NOT EXISTS "${Data}")
+  message(SEND_ERROR "Input file:\n  ${Data}\ndoes not exist!")
+endif()
+if(NOT EXISTS "${Other}")
+  message(SEND_ERROR "Input file:\n  ${Other}\ndoes not exist!")
+endif()
+# Verify that the 'Data' object was found in the second store location left
+# from Data1 target downloads and that the 'Other' object was found in the
+# first store location left from Data3 target downloads.  Neither object
+# should exist in the opposite store.
+foreach(should_exist
+    "${Store0}/MD5/aaad162b85f60d1eb57ca71a23e8efd7"
+    "${Store1}/MD5/8c018830e3efa5caf3c7415028335a57"
+    )
+  if(NOT EXISTS ${should_exist})
+    message(SEND_ERROR "Store file:\n  ${should_exist}\nshould exist!")
+  endif()
+endforeach()
+foreach(should_not_exist
+    "${Store0}/MD5/8c018830e3efa5caf3c7415028335a57"
+    "${Store1}/MD5/aaad162b85f60d1eb57ca71a23e8efd7"
+    )
+  if(EXISTS ${should_not_exist})
+    message(SEND_ERROR "Store file:\n  ${should_not_exist}\nshould not exist!")
+  endif()
+endforeach()

Tests/Module/ExternalData/Data4/Other.dat.md5

@@ -0,0 +1 @@
+aaad162b85f60d1eb57ca71a23e8efd7

Tests/RunCMake/ExternalData/NoURLTemplates-stderr.txt

@@ -1,5 +1,5 @@
 CMake Error at .*/Modules/ExternalData.cmake:[0-9]+ \(message\):
-  ExternalData_URL_TEMPLATES is not set!
+  Neither ExternalData_URL_TEMPLATES nor ExternalData_OBJECT_STORES is set!
 Call Stack \(most recent call first\):
   NoURLTemplates.cmake:2 \(ExternalData_Add_Target\)
   CMakeLists.txt:3 \(include\)

Tests/RunCMake/ExternalData/ObjectStoreOnly.cmake

@@ -0,0 +1,3 @@
+include(ExternalData)
+set(ExternalData_OBJECT_STORES "${CMAKE_CURRENT_BINARY_DIR}")
+ExternalData_Add_Target(Data)

Tests/RunCMake/ExternalData/RunCMakeTest.cmake

@@ -22,6 +22,7 @@ run_cmake(NormalData2)
 run_cmake(NormalData3)
 run_cmake(NormalDataSub1)
 run_cmake(NotUnderRoot)
+run_cmake(ObjectStoreOnly)
 run_cmake(Semicolon1)
 run_cmake(Semicolon2)
 run_cmake(Semicolon3)