[Clang] Do not check if we are in a discared context in non-immediate contexts

[cor3ntin]

Summary

This fixes in a regression introduced by 6eeda06c1.

When deducing the return type of nested function calls, only the
return type of the outermost expression should be ignored.

Instead of assuming all contextes nested in a discared statements
are themselves discarded, only assume that in immediate contexts.

Similarly, only consider contextes immediately in an immediate or
discarded statement as being themselves immediate.

[cor3ntin]

clang-format

[aaron.ballman]

LGTM me, I'll land shortly on your behalf.

[aaron.ballman]

Thanks for the quick fix! I've landed on your behalf in 2334314550724812bb94e36c6b5df7d665bdbd9d

clang/include/clang/Sema/Sema.h

struct ExpressionEvaluationContextRecord {
 
     bool isConstantEvaluated() const {
       return Context == ExpressionEvaluationContext::ConstantEvaluated ||
              Context == ExpressionEvaluationContext::ImmediateFunctionContext;
     }
 
     bool isImmediateFunctionContext() const {
       return Context == ExpressionEvaluationContext::ImmediateFunctionContext ||
-             InImmediateFunctionContext;
+             (Context == ExpressionEvaluationContext::DiscardedStatement &&
+              InImmediateFunctionContext);
     }
 
     bool isDiscardedStatementContext() const {
       return Context == ExpressionEvaluationContext::DiscardedStatement ||
-             InDiscardedStatement;
+             (Context ==
+                  ExpressionEvaluationContext::ImmediateFunctionContext &&
+              InDiscardedStatement);
     }
   };
 
   /// A stack of expression evaluation contexts.
   SmallVector<ExpressionEvaluationContextRecord, 8> ExprEvalContexts;
 
   /// Emit a warning for all pending noderef expressions that we recorded.
   void WarnOnPendingNoDerefs(ExpressionEvaluationContextRecord &Rec);

clang/test/CXX/stmt.stmt/stmt.select/stmt.if/p2.cpp

void evil_things() {
     if constexpr (true || ({evil_label: false;})) {} // expected-note {{constexpr if}}
 
     if constexpr (true) // expected-note {{constexpr if}}
       goto surprise; // expected-error {{cannot jump}}
     else
       surprise: {}
   }
 }
+
+namespace deduced_return_type_in_discareded_statement {
+
+template <typename T>
+auto a(const T &t) {
+  return t;
+}
+
+void f() {
+  if constexpr (false) {
+    a(a(0));
+  }
+}
+} // namespace deduced_return_type_in_discareded_statement
+
 #endif