Diagnose a conflicting silgen_name/extern(c) name instead of asserting/crashing

Author: kubamracek

include/swift/AST/DiagnosticsSIL.def

@@ -121,6 +121,11 @@ ERROR(unsupported_variadic_function_abstraction,none,
       "convention; try wrapping it in a struct",
       (Type))
 
+ERROR(function_type_mismatch,none,
+      "function type mismatch, declared as %0 but used as %1", (Type, Type))
+NOTE(function_declared_here,none,
+     "function declared here", ())
+
 // Capture before declaration diagnostics.
 ERROR(capture_before_declaration,none,
       "closure captures %0 before it is declared", (Identifier))

lib/SILGen/SILGenThunk.cpp

@@ -163,14 +163,22 @@ SILGenFunction::emitGlobalFunctionRef(SILLocation loc, SILDeclRef constant,
   }
 
   auto f = SGM.getFunction(constant, NotForDefinition);
-#ifndef NDEBUG
+
   auto constantFnTypeInContext =
-    SGM.Types.getLoweredType(constantInfo.SILFnType,
-                             B.getTypeExpansionContext())
-             .castTo<SILFunctionType>();
-  assert(f->getLoweredFunctionTypeInContext(B.getTypeExpansionContext())
-          == constantFnTypeInContext);
-#endif
+      SGM.Types
+          .getLoweredType(constantInfo.SILFnType, B.getTypeExpansionContext())
+          .castTo<SILFunctionType>();
+  auto existingType =
+      f->getLoweredFunctionTypeInContext(B.getTypeExpansionContext());
+  if (existingType != constantFnTypeInContext) {
+    // This can happen for example when using @_silgen_name or @_extern(c)
+    // attributes
+    SGM.diagnose(loc.getSourceLoc(), diag::function_type_mismatch, existingType,
+                 constantFnTypeInContext);
+    SGM.diagnose(f->getLocation().getSourceLoc(), diag::function_declared_here);
+    return SILUndef::get(constantInfo.getSILType(), F);
+  }
+
   if (callPreviousDynamicReplaceableImpl)
     return B.createPreviousDynamicFunctionRef(loc, f);
   else

test/SILGen/silgen_name_conflict.swift

@@ -0,0 +1,21 @@
+// RUN: %target-swift-emit-silgen %s -enable-experimental-feature Extern -verify
+
+@_silgen_name("my_extern_func")
+func my_extern_func1() // expected-note {{function declared here}}
+
+@_silgen_name("my_extern_func")
+func my_extern_func2(x: Int)
+
+@_extern(c, "my_other_extern_func")
+func my_other_extern_func1() // expected-note {{function declared here}}
+
+@_extern(c, "my_other_extern_func")
+func my_other_extern_func2(x: Int)
+
+public func foo() {
+    my_extern_func1()
+    my_extern_func2(x: 42) // expected-error {{function type mismatch, declared as '@convention(thin) () -> ()' but used as '@convention(thin) (Int) -> ()'}}
+
+    my_other_extern_func1()
+    my_other_extern_func2(x: 42) // expected-error {{function type mismatch, declared as '@convention(c) () -> ()' but used as '@convention(c) (Int) -> ()'}}
+}