[clang] [Sema] Warn about omitting deprecated enumerator in switch (PR #138562)

[Hans Wennborg via cfe-commits]

https://github.com/zmodem updated https://github.com/llvm/llvm-project/pull/138562

>From e221ba3b0f7b08bcfc56bf75f7505265c332637d Mon Sep 17 00:00:00 2001
From: Hans Wennborg <hans at chromium.org>
Date: Mon, 5 May 2025 20:24:15 +0200
Subject: [PATCH 1/2] [Sema] Warn about omitting deprecated enumerator in
 switch

This undoes part of 3e4e3b17c14c15c23c0ed18ca9165b42b1b13ae3 which
added the "Omitting a deprecated constant is ok; it should never
materialize." logic.

That seems wrong: deprecated means the enumerator is likely to be
removed in future versions, not that it canot materialize.
---
 clang/lib/Sema/SemaStmt.cpp           | 6 +++++-
 clang/test/Sema/switch-availability.c | 2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index e8c1f8490342a..990d2fadaf5aa 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -1667,8 +1667,12 @@ Sema::ActOnFinishSwitchStmt(SourceLocation SwitchLoc, Stmt *Switch,
         // Don't warn about omitted unavailable EnumConstantDecls.
         switch (EI->second->getAvailability()) {
         case AR_Deprecated:
-          // Omitting a deprecated constant is ok; it should never materialize.
+          // Deprecated enumerators still need to be handled: they may be
+          // deprecated, but can still occur.
+          break;
+
         case AR_Unavailable:
+          // Omitting an unavailable enumerator is ok; it should never occur.
           continue;
 
         case AR_NotYetIntroduced:
diff --git a/clang/test/Sema/switch-availability.c b/clang/test/Sema/switch-availability.c
index 888edddac463d..b4f8726addc0b 100644
--- a/clang/test/Sema/switch-availability.c
+++ b/clang/test/Sema/switch-availability.c
@@ -15,7 +15,7 @@ enum SwitchTwo {
 };
 
 void testSwitchTwo(enum SwitchTwo st) {
-  switch (st) {} // expected-warning{{enumeration values 'Vim' and 'Emacs' not handled in switch}}
+  switch (st) {} // expected-warning{{enumeration values 'Ed', 'Vim' and 'Emacs' not handled in switch}}
 }
 
 enum SwitchThree {

>From 6bc923d27d77009b37de12c9e33d2e83835d6a4d Mon Sep 17 00:00:00 2001
From: Hans Wennborg <hans at chromium.org>
Date: Tue, 6 May 2025 09:31:50 +0200
Subject: [PATCH 2/2] check for -Wreturn-type

---
 clang/test/Sema/switch-availability.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/clang/test/Sema/switch-availability.c b/clang/test/Sema/switch-availability.c
index b4f8726addc0b..137cdc976ec2d 100644
--- a/clang/test/Sema/switch-availability.c
+++ b/clang/test/Sema/switch-availability.c
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -verify -Wswitch -triple x86_64-apple-macosx10.12 %s
+// RUN: %clang_cc1 -verify -Wswitch -Wreturn-type -triple x86_64-apple-macosx10.12 %s
 
 enum SwitchOne {
   Unavail __attribute__((availability(macos, unavailable))),
@@ -25,3 +25,16 @@ enum SwitchThree {
 void testSwitchThree(enum SwitchThree st) {
   switch (st) {} // expected-warning{{enumeration value 'New' not handled in switch}}
 }
+
+enum SwitchFour {
+  Red,
+  Green,
+  Blue [[deprecated]]
+};
+
+int testSwitchFour(enum SwitchFour e) {
+  switch (e) { // expected-warning{{enumeration value 'Blue' not handled in switch}}
+  case Red:   return 1;
+  case Green: return 2;
+  }
+} // expected-warning{{non-void function does not return a value in all control paths}}