[clang] [clang-repl] Suppress [[nodiscard]] warnings for REPL printed express (PR #178661)

[via cfe-commits]

https://github.com/bala-bhargav updated https://github.com/llvm/llvm-project/pull/178661

>From e0a73df5b689ba2a22d1bb866817976d9f1da528 Mon Sep 17 00:00:00 2001
From: bhargav <penugondabalabharghav at gmail.com>
Date: Thu, 12 Feb 2026 15:38:32 +0530
Subject: [PATCH] [clang-repl] Suppress [[nodiscard]] warnings for REPL printed
 expressions

In clang-repl, expressions typed without a semicolon have their values
printed by the value printing mechanism. Since the result is used (for
printing), we should not emit [[nodiscard]] warnings for these
expressions.

This suppresses warn_unused_result alongside the existing
warn_unused_expr suppression in Interpreter::Parse(), following the
same pattern already established for unused expression warnings.

Fixes #178595
---
 clang/lib/Interpreter/Interpreter.cpp |  6 ++++++
 clang/test/Interpreter/nodiscard.cpp  | 20 ++++++++++++++++++++
 2 files changed, 26 insertions(+)
 create mode 100644 clang/test/Interpreter/nodiscard.cpp

diff --git a/clang/lib/Interpreter/Interpreter.cpp b/clang/lib/Interpreter/Interpreter.cpp
index 9c94cfa5ee381..3eef722541eb8 100644
--- a/clang/lib/Interpreter/Interpreter.cpp
+++ b/clang/lib/Interpreter/Interpreter.cpp
@@ -469,6 +469,12 @@ Interpreter::Parse(llvm::StringRef Code) {
   // printing could cause it.
   getCompilerInstance()->getDiagnostics().setSeverity(
       clang::diag::warn_unused_expr, diag::Severity::Ignored, SourceLocation());
+  // Suppress [[nodiscard]] warnings during parsing since we don't know yet
+  // if the expression has a missing semicolon (value printed) or not.
+  // If the value is printed, it's considered "used" so no warning is needed.
+  getCompilerInstance()->getDiagnostics().setSeverity(
+      clang::diag::warn_unused_result, diag::Severity::Ignored,
+      SourceLocation());
 
   llvm::Expected<TranslationUnitDecl *> TuOrErr = IncrParser->Parse(Code);
   if (!TuOrErr)
diff --git a/clang/test/Interpreter/nodiscard.cpp b/clang/test/Interpreter/nodiscard.cpp
new file mode 100644
index 0000000000000..bf307ee81835e
--- /dev/null
+++ b/clang/test/Interpreter/nodiscard.cpp
@@ -0,0 +1,20 @@
+// REQUIRES: host-supports-jit
+// RUN: cat %s | clang-repl 2>&1 | FileCheck %s
+
+// Test that [[nodiscard]] warnings are suppressed for REPL top-level
+// expressions that will have their values printed (no semicolon).
+
+extern "C" int printf(const char*,...);
+
+[[nodiscard]] int getValue() { return 42; }
+
+// No warning when expression value is printed (no semicolon)
+getValue()
+// CHECK: (int) 42
+
+// Verify assignment doesn't warn
+int x = getValue();
+printf("x = %d\n", x);
+// CHECK: x = 42
+
+%quit