[clang-repl] Extend the C support. (#89804)

The IdResolver chain is the main way for C to implement lookup rules.
Every new partial translation unit caused clang to exit the top-most
scope which in turn cleaned up the IdResolver chain. That was not an
issue for C++ because its lookup is implemented on the level of
declaration contexts.

This patch keeps the IdResolver chain across partial translation units
maintaining proper C-style lookup infrastructure.

1 files changed, 7 insertions, 3 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 6764a97..7f6921e 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2282,9 +2282,13 @@ void Sema::ActOnPopScope(SourceLocation Loc, Scope *S) {
     if (LabelDecl *LD = dyn_cast<LabelDecl>(D))
       CheckPoppedLabel(LD, *this, addDiag);
 
-    // Remove this name from our lexical scope, and warn on it if we haven't
-    // already.
-    IdResolver.RemoveDecl(D);
+    // Partial translation units that are created in incremental processing must
+    // not clean up the IdResolver because PTUs should take into account the
+    // declarations that came from previous PTUs.
+    if (!PP.isIncrementalProcessingEnabled())
+      IdResolver.RemoveDecl(D);
+
+    // Warn on it if we are shadowing a declaration.
     auto ShadowI = ShadowingDecls.find(D);
     if (ShadowI != ShadowingDecls.end()) {
       if (const auto *FD = dyn_cast<FieldDecl>(ShadowI->second)) {