[C++20][Modules] Improve handing of Private Module Fragment diagnostics.

This adds a check for exported inline functions, that there is a definition in
the definition domain (which, in practice, can only be the module purview but
before any PMF starts) since the PMF definition domain cannot contain exports.

This is:
[dcl.inline]/7
If an inline function or variable that is attached to a named module is declared in
a definition domain, it shall be defined in that domain.

The patch also amends diagnostic output by excluding the PMF sub-module from the
set considered as sources of missing decls.  There is no point in telling the user
that the import of a PMF object is missing - since such objects are never reachable
to an importer.  We still show the definition (as unreachable), to help point out
this.

Differential Revision: https://reviews.llvm.org/D128328

1 files changed, 11 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaModule.cpp b/clang/lib/Sema/SemaModule.cpp
index 757c611..b205fd9 100644
--- a/clang/lib/Sema/SemaModule.cpp
+++ b/clang/lib/Sema/SemaModule.cpp
@@ -910,6 +910,17 @@ Decl *Sema::ActOnFinishExportDecl(Scope *S, Decl *D, SourceLocation RBraceLoc) {
         diagExportedUnnamedDecl(*this, UnnamedDeclKind::Context, Child,
                                 BlockStart);
       }
+      if (auto *FD = dyn_cast<FunctionDecl>(Child)) {
+        // [dcl.inline]/7
+        // If an inline function or variable that is attached to a named module
+        // is declared in a definition domain, it shall be defined in that
+        // domain.
+        // So, if the current declaration does not have a definition, we must
+        // check at the end of the TU (or when the PMF starts) to see that we
+        // have a definition at that point.
+        if (FD->isInlineSpecified() && !FD->isDefined())
+          PendingInlineFuncDecls.insert(FD);
+      }
     }
   }