Genex: Add policy to handle empty list items in $<IN_LIST:...>

The old behavior of $<IN_LIST:...> is inconsistent with that of
if(IN_LIST), in that it does not find an empty search item even if
the list contains empty items. This change adds a new policy to
correctly handle empty items and make the behavior more consistent
with if(IN_LIST).

Fixes: #18556

8 files changed, 73 insertions, 0 deletions

diff --git a/Tests/RunCMake/GeneratorExpression/CMP0085-NEW-check.cmake b/Tests/RunCMake/GeneratorExpression/CMP0085-NEW-check.cmake
new file mode 100644
index 0000000..520bf3d
--- /dev/null
+++ b/Tests/RunCMake/GeneratorExpression/CMP0085-NEW-check.cmake
@@ -0,0 +1,6 @@
+file(READ "${RunCMake_TEST_BINARY_DIR}/CMP0085-NEW-generated.txt" content)
+
+set(expected "101011")
+if(NOT content STREQUAL expected)
+  set(RunCMake_TEST_FAILED "actual content:\n [[${content}]]\nbut expected:\n [[${expected}]]")
+endif()
diff --git a/Tests/RunCMake/GeneratorExpression/CMP0085-NEW.cmake b/Tests/RunCMake/GeneratorExpression/CMP0085-NEW.cmake
new file mode 100644
index 0000000..ee85c0d
--- /dev/null
+++ b/Tests/RunCMake/GeneratorExpression/CMP0085-NEW.cmake
@@ -0,0 +1,4 @@
+cmake_policy(SET CMP0070 NEW)
+file(GENERATE OUTPUT CMP0085-NEW-generated.txt CONTENT
+  "$<IN_LIST:,>$<IN_LIST:,a>$<IN_LIST:,;a>$<IN_LIST:a,>$<IN_LIST:a,a>$<IN_LIST:a,;a>"
+  )
diff --git a/Tests/RunCMake/GeneratorExpression/CMP0085-OLD-check.cmake b/Tests/RunCMake/GeneratorExpression/CMP0085-OLD-check.cmake
new file mode 100644
index 0000000..c387db7
--- /dev/null
+++ b/Tests/RunCMake/GeneratorExpression/CMP0085-OLD-check.cmake
@@ -0,0 +1,6 @@
+file(READ "${RunCMake_TEST_BINARY_DIR}/CMP0085-OLD-generated.txt" content)
+
+set(expected "000011")
+if(NOT content STREQUAL expected)
+  set(RunCMake_TEST_FAILED "actual content:\n [[${content}]]\nbut expected:\n [[${expected}]]")
+endif()
diff --git a/Tests/RunCMake/GeneratorExpression/CMP0085-OLD.cmake b/Tests/RunCMake/GeneratorExpression/CMP0085-OLD.cmake
new file mode 100644
index 0000000..31b6a51
--- /dev/null
+++ b/Tests/RunCMake/GeneratorExpression/CMP0085-OLD.cmake
@@ -0,0 +1,4 @@
+cmake_policy(SET CMP0070 NEW)
+file(GENERATE OUTPUT CMP0085-OLD-generated.txt CONTENT
+  "$<IN_LIST:,>$<IN_LIST:,a>$<IN_LIST:,;a>$<IN_LIST:a,>$<IN_LIST:a,a>$<IN_LIST:a,;a>"
+  )
diff --git a/Tests/RunCMake/GeneratorExpression/CMP0085-WARN-check.cmake b/Tests/RunCMake/GeneratorExpression/CMP0085-WARN-check.cmake
new file mode 100644
index 0000000..f7bcf0f
--- /dev/null
+++ b/Tests/RunCMake/GeneratorExpression/CMP0085-WARN-check.cmake
@@ -0,0 +1,6 @@
+file(READ "${RunCMake_TEST_BINARY_DIR}/CMP0085-WARN-generated.txt" content)
+
+set(expected "000011")
+if(NOT content STREQUAL expected)
+  set(RunCMake_TEST_FAILED "actual content:\n [[${content}]]\nbut expected:\n [[${expected}]]")
+endif()
diff --git a/Tests/RunCMake/GeneratorExpression/CMP0085-WARN-stderr.txt b/Tests/RunCMake/GeneratorExpression/CMP0085-WARN-stderr.txt
new file mode 100644
index 0000000..81bd450
--- /dev/null
+++ b/Tests/RunCMake/GeneratorExpression/CMP0085-WARN-stderr.txt
@@ -0,0 +1,33 @@
+CMake Warning \(dev\) at CMP0085-WARN\.cmake:[0-9]+ \(file\):
+  Policy CMP0085 is not set: \$<IN_LIST:\.\.\.> handles empty list items\.  Run
+  "cmake --help-policy CMP0085" for policy details\.  Use the cmake_policy
+  command to set the policy and suppress this warning\.
+
+  Search Item:
+
+    ""
+
+  List:
+
+    ""
+
+Call Stack \(most recent call first\):
+  CMakeLists\.txt:[0-9]+ \(include\)
+This warning is for project developers\.  Use -Wno-dev to suppress it\.
+
+CMake Warning \(dev\) at CMP0085-WARN\.cmake:[0-9]+ \(file\):
+  Policy CMP0085 is not set: \$<IN_LIST:\.\.\.> handles empty list items\.  Run
+  "cmake --help-policy CMP0085" for policy details\.  Use the cmake_policy
+  command to set the policy and suppress this warning\.
+
+  Search Item:
+
+    ""
+
+  List:
+
+    ";a"
+
+Call Stack \(most recent call first\):
+  CMakeLists\.txt:[0-9]+ \(include\)
+This warning is for project developers\.  Use -Wno-dev to suppress it\.
diff --git a/Tests/RunCMake/GeneratorExpression/CMP0085-WARN.cmake b/Tests/RunCMake/GeneratorExpression/CMP0085-WARN.cmake
new file mode 100644
index 0000000..59c7826
--- /dev/null
+++ b/Tests/RunCMake/GeneratorExpression/CMP0085-WARN.cmake
@@ -0,0 +1,4 @@
+cmake_policy(SET CMP0070 NEW)
+file(GENERATE OUTPUT CMP0085-WARN-generated.txt CONTENT
+  "$<IN_LIST:,>$<IN_LIST:,a>$<IN_LIST:,;a>$<IN_LIST:a,>$<IN_LIST:a,a>$<IN_LIST:a,;a>"
+  )
diff --git a/Tests/RunCMake/GeneratorExpression/RunCMakeTest.cmake b/Tests/RunCMake/GeneratorExpression/RunCMakeTest.cmake
index 3905c5f..013117e 100644
--- a/Tests/RunCMake/GeneratorExpression/RunCMakeTest.cmake
+++ b/Tests/RunCMake/GeneratorExpression/RunCMakeTest.cmake
@@ -61,3 +61,13 @@ if(LINKER_SUPPORTS_PDB)
 else()
   run_cmake(NonValidCompiler-TARGET_PDB_FILE)
 endif()
+
+set(RunCMake_TEST_OPTIONS -DCMAKE_POLICY_DEFAULT_CMP0085:STRING=OLD)
+run_cmake(CMP0085-OLD)
+unset(RunCMake_TEST_OPTIONS)
+
+run_cmake(CMP0085-WARN)
+
+set(RunCMake_TEST_OPTIONS -DCMAKE_POLICY_DEFAULT_CMP0085:STRING=NEW)
+run_cmake(CMP0085-NEW)
+unset(RunCMake_TEST_OPTIONS)