Merge pull request swiftlang#78441 from stzn/improve-use-before-initialized-diagnostic

[Diagnostics] A self argument implicitly passed as an inout parameter is diagnosed as used before initialized

Author: eeckstein

lib/SILOptimizer/Mandatory/DefiniteInitialization.cpp

@@ -1734,8 +1734,13 @@ void LifetimeChecker::handleInOutUse(const DIMemoryUse &Use) {
       return;
     }
 
-    auto diagID = diag::variable_inout_before_initialized;
-    
+    // A self argument implicitly passed as an inout parameter is diagnosed as
+    // "used before initialized", because "passed by reference" might be a
+    // confusing diagnostic in this context.
+    auto diagID = (Use.Kind == DIUseKind::InOutSelfArgument)
+                      ? diag::variable_used_before_initialized
+                      : diag::variable_inout_before_initialized;
+
     if (isa<AddressToPointerInst>(Use.Inst))
       diagID = diag::variable_addrtaken_before_initialized;
 

test/SILOptimizer/definite_init_address_only_let.swift

@@ -29,3 +29,13 @@ func bas<T>(a: Bool, t: T) {
 
   x = t
 }
+
+func quz<T>(a: Bool, t: T) {
+  let closure: (inout T) -> Void = { _ in }
+  var x: T // expected-note {{defined here}}
+  defer { closure(&x) } // expected-error{{variable 'x' passed by reference before being initialized}}
+  if a {
+    x = t
+    return
+  }
+}

test/SILOptimizer/definite_init_diagnostics.swift

@@ -125,6 +125,18 @@ func test2() {
   // expected-note@+1 {{'u2' declared here}}
   unowned let u2 = SomeClass()
   _ = u2                // ok
+
+  // Array
+  var arr1: [String] // expected-note {{variable defined here}}
+  arr1.append("item") // expected-error {{variable 'arr1' used before being initialized}}
+  var arr2: [String] = []
+  arr2.append("item") // ok
+
+  // Dictionary
+  var d1: [String: Int] // expected-note {{variable defined here}}
+  d1["key"] = 1 // expected-error {{variable 'd1' used before being initialized}}
+  var d2: [String: Int] = [:]
+  d2["key"] = 1 // ok
 }
 
 
@@ -1483,8 +1495,7 @@ func testOptionalChainingWithGenerics<T: DIOptionalTestProtocol>(p: T) -> T? {
             // expected-note@-2 {{constant defined here}}
 
   // note that here assignment to 'f' is a call to the setter.
-  x?.f = 0  // expected-error {{constant 'x' used before being initialized}}
-            // expected-error@-1 {{constant 'x' passed by reference before being initialized}}
+  x?.f = 0  // expected-error 2 {{constant 'x' used before being initialized}}
   return x  // expected-error {{constant 'x' used before being initialized}}
 }