cmCxxModuleMapper: Fix transitive requirements computation

Previously CMake may generate incomplete transitive requirements in
CMakeFiles/<target>.dir/CXXModules.json and therefore in module mapper
for compiler, when source files were listed in CMakeList.txt in a
certain order.

This commit fixes the problem by correctly tracking unfinished
transitive requirements computation of module units.

There have been a simple circular test case whose circular dependency
was reported by build system. Now with this correct implementation it's
reported by CMake generating module mappers.

Add two test cases for transitive requirements computation, one with
adding source files in hardcoded order, and the other in randomized
order.

Fixes: #25465

1 files changed, 8 insertions, 0 deletions

diff --git a/Tests/RunCMake/CXXModules/examples/non-trivial-collation-order/partition_level/intf4.cxx b/Tests/RunCMake/CXXModules/examples/non-trivial-collation-order/partition_level/intf4.cxx
new file mode 100644
index 0000000..2826717
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/non-trivial-collation-order/partition_level/intf4.cxx
@@ -0,0 +1,8 @@
+export module partition_level:intf4;
+export import :intf3;
+namespace partition_level {
+int intf4()
+{
+  return intf3();
+}
+}