[flang] Fix crash with USE of hermetic module file

[klausler]

When one hermetic module file uses another, a later compilation may crash in semantics when it itself is used, since the module file reader sets the "current hermetic module file scope" to null after reading one rather than saving and restoring that pointer.

[llvmbot]

@llvm/pr-subscribers-flang-semantics

Author: Peter Klausler (klausler)

Changes

When one hermetic module file uses another, a later compilation may crash in semantics when it itself is used, since the module file reader sets the "current hermetic module file scope" to null after reading one rather than saving and restoring that pointer.

---

Full diff: https://github.com/llvm/llvm-project/pull/138785.diff

2 Files Affected:

• (modified) flang/lib/Semantics/mod-file.cpp (+2-1)
• (added) flang/test/Semantics/modfile75.F90 (+17)

diff --git a/flang/lib/Semantics/mod-file.cpp b/flang/lib/Semantics/mod-file.cpp
index ee356e56e4458..3df229cc85587 100644
--- a/flang/lib/Semantics/mod-file.cpp
+++ b/flang/lib/Semantics/mod-file.cpp
@@ -1537,6 +1537,7 @@ Scope *ModFileReader::Read(SourceName name, std::optional<bool> isIntrinsic,
   // created under -fhermetic-module-files?  If so, process them first in
   // their own nested scope that will be visible only to USE statements
   // within the module file.
+  Scope *previousHermetic{context_.currentHermeticModuleFileScope()};
   if (parseTree.v.size() > 1) {
     parser::Program hermeticModules{std::move(parseTree.v)};
     parseTree.v.emplace_back(std::move(hermeticModules.v.front()));
@@ -1552,7 +1553,7 @@ Scope *ModFileReader::Read(SourceName name, std::optional<bool> isIntrinsic,
   GetModuleDependences(context_.moduleDependences(), sourceFile->content());
   ResolveNames(context_, parseTree, topScope);
   context_.foldingContext().set_moduleFileName(wasModuleFileName);
-  context_.set_currentHermeticModuleFileScope(nullptr);
+  context_.set_currentHermeticModuleFileScope(previousHermetic);
   if (!moduleSymbol) {
     // Submodule symbols' storage are owned by their parents' scopes,
     // but their names are not in their parents' dictionaries -- we
diff --git a/flang/test/Semantics/modfile75.F90 b/flang/test/Semantics/modfile75.F90
new file mode 100644
index 0000000000000..e8cfb13552437
--- /dev/null
+++ b/flang/test/Semantics/modfile75.F90
@@ -0,0 +1,17 @@
+!RUN: (%flang -c -DWHICH=1 %s && %flang -c -DWHICH=2 %s && %flang_fc1 -fdebug-unparse %s) | FileCheck %s
+
+#if WHICH == 1
+module m1
+  use iso_c_binding
+end
+#elif WHICH == 2
+module m2
+  use m1
+end
+#else
+program test
+  use m2
+!CHECK: INTEGER(KIND=4_4) n
+  integer(c_int) n
+end
+#endif

[jeanPerier]

Something is broken here. See buildbots "flang/test/Semantics/modfile75.F90:15:11: error: Must be a constant value".

I am thinking this could be a lit "race" with module file (I am not sure, but I think all the tests are ran in the same directory in parallel, which would cause the issue since m1 are common names and could be overridden before the final part of the test).

[akuhlens]

LGTM