[Diagnostics] Offer 'is' replacement for unused 'if let' expression with optional operand

lib/Sema/MiscDiagnostics.cpp

@@ -2888,23 +2888,41 @@ VarDeclUsageChecker::~VarDeclUsageChecker() {
 
                   // If the subexpr is an "as?" cast, we can rewrite it to
                   // be an "is" test.
-                  bool isIsTest = false;
-                  if (isa<ConditionalCheckedCastExpr>(initExpr) &&
-                      !initExpr->isImplicit()) {
-                    noParens = isIsTest = true;
+                  ConditionalCheckedCastExpr *CCE = nullptr;
+
+                  // initExpr can be wrapped inside parens or try expressions.
+                  if (auto ccExpr = dyn_cast<ConditionalCheckedCastExpr>(
+                          initExpr->getValueProvidingExpr())) {
+                    if (!ccExpr->isImplicit()) {
+                      CCE = ccExpr;
+                      noParens = true;
+                    }
                   }
-
+
+                  // In cases where the value is optional, the cast expr is
+                  // wrapped inside OptionalEvaluationExpr. Unwrap it to get
+                  // ConditionalCheckedCastExpr.
+                  if (auto oeExpr = dyn_cast<OptionalEvaluationExpr>(
+                          initExpr->getValueProvidingExpr())) {
+                    if (auto ccExpr = dyn_cast<ConditionalCheckedCastExpr>(
+                            oeExpr->getSubExpr()->getValueProvidingExpr())) {
+                      if (!ccExpr->isImplicit()) {
+                        CCE = ccExpr;
+                        noParens = true;
+                      }
+                    }
+                  }
+
                   auto diagIF = Diags.diagnose(var->getLoc(),
                                                diag::pbd_never_used_stmtcond,
                                             var->getName());
                   auto introducerLoc = SC->getCond()[0].getIntroducerLoc();
                   diagIF.fixItReplaceChars(introducerLoc,
                                            initExpr->getStartLoc(),
                                            &"("[noParens]);
-                  
-                  if (isIsTest) {
+
+                  if (CCE) {
                     // If this was an "x as? T" check, rewrite it to "x is T".
-                    auto CCE = cast<ConditionalCheckedCastExpr>(initExpr);
                     diagIF.fixItReplace(SourceRange(CCE->getLoc(),
                                                     CCE->getQuestionLoc()),
                                         "is");

test/decl/var/usage.swift

@@ -330,8 +330,44 @@ func test(_ a : Int?, b : Any) {
   if let x = b as? Int {  // expected-warning {{value 'x' was defined but never used; consider replacing with boolean test}} {{6-14=}} {{16-19=is}}
   }
 
-  // SR-1112
+  // SR-14646. Special case, turn this into an 'is' test with optional value. 
+  let bb: Any? = 3
+  if let bbb = bb as? Int {}  // expected-warning {{value 'bbb' was defined but never used; consider replacing with boolean test}} {{6-16=}} {{19-22=is}}
+  if let bbb = (bb) as? Int {}  // expected-warning {{value 'bbb' was defined but never used; consider replacing with boolean test}} {{6-16=}} {{21-24=is}}
+
+  func aa() -> Any? { return 1 }
+  if let aaa = aa() as? Int {} // expected-warning {{value 'aaa' was defined but never used; consider replacing with boolean test}} {{6-16=}} {{21-24=is}}
+  if let aaa = (aa()) as? Int {} // expected-warning {{value 'aaa' was defined but never used; consider replacing with boolean test}} {{6-16=}} {{23-26=is}}
+
+  func bb() -> Any { return 1 }
+  if let aaa = aa() as? Int {} // expected-warning {{value 'aaa' was defined but never used; consider replacing with boolean test}} {{6-16=}} {{21-24=is}}
+  if let aaa = (aa()) as? Int {} // expected-warning {{value 'aaa' was defined but never used; consider replacing with boolean test}} {{6-16=}} {{23-26=is}}
 
+
+  func throwingAA() throws -> Any? { return 1 }
+  do {
+    if let aaa = try! throwingAA() as? Int {} // expected-warning {{value 'aaa' was defined but never used; consider replacing with boolean test}} {{8-18=}} {{36-39=is}}
+    if let aaa = (try! throwingAA()) as? Int {} // expected-warning {{value 'aaa' was defined but never used; consider replacing with boolean test}} {{8-18=}} {{38-41=is}}
+    if let aaa = try throwingAA() as? Int {} // expected-warning {{value 'aaa' was defined but never used; consider replacing with boolean test}} {{8-18=}} {{35-38=is}}
+    if let aaa = (try throwingAA()) as? Int {} // expected-warning {{value 'aaa' was defined but never used; consider replacing with boolean test}} {{8-18=}} {{37-40=is}}
+  } catch { }
+  if let aaa = try? throwingAA() as? Int {} // expected-warning {{value 'aaa' was defined but never used; consider replacing with boolean test}} {{6-16=(}} {{41-41=) != nil}}
+  if let aaa = (try? throwingAA()) as? Int {} // expected-warning {{value 'aaa' was defined but never used; consider replacing with boolean test}} {{6-16=}} {{36-39=is}}
+
+  func throwingBB() throws -> Any { return 1 }
+  do { 
+    if let bbb = try! throwingBB() as? Int {} // expected-warning {{value 'bbb' was defined but never used; consider replacing with boolean test}} {{8-18=}} {{36-39=is}}
+    if let bbb = (try! throwingBB()) as? Int {} // expected-warning {{value 'bbb' was defined but never used; consider replacing with boolean test}} {{8-18=}} {{38-41=is}}
+    if let bbb = try throwingBB() as? Int {} // expected-warning {{value 'bbb' was defined but never used; consider replacing with boolean test}} {{8-18=}} {{35-38=is}}
+    if let bbb = (try throwingBB()) as? Int {} // expected-warning {{value 'bbb' was defined but never used; consider replacing with boolean test}} {{8-18=}} {{37-40=is}}
+  } catch { }
+  if let bbb = try? throwingBB() as? Int {} // expected-warning {{value 'bbb' was defined but never used; consider replacing with boolean test}} {{6-16=(}} {{41-41=) != nil}}
+  if let bbb = (try? throwingBB()) as? Int {} // expected-warning {{value 'bbb' was defined but never used; consider replacing with boolean test}} {{6-16=}} {{36-39=is}}
+
+  let cc: (Any?, Any) = (1, 2)
+  if let (cc1, cc2) = cc as? (Int, Int) {} // expected-warning {{immutable value 'cc1' was never used; consider replacing with '_' or removing it}} expected-warning {{immutable value 'cc2' was never used; consider replacing with '_' or removing it}}
+
+  // SR-1112
   let xxx: Int? = 0
 
   if let yyy = xxx { } // expected-warning{{with boolean test}} {{6-16=}} {{19-19= != nil}}
@@ -356,7 +392,7 @@ let optionalString: String? = "check"
 if let string = optionalString {}  // expected-warning {{value 'string' was defined but never used; consider replacing with boolean test}} {{4-17=}} {{31-31= != nil}}
 
 let optionalAny: Any? = "check"
-if let string = optionalAny as? String {} // expected-warning {{value 'string' was defined but never used; consider replacing with boolean test}} {{4-17=(}} {{39-39=) != nil}}
+if let string = optionalAny as? String {} // expected-warning {{value 'string' was defined but never used; consider replacing with boolean test}} {{4-17=}} {{29-32=is}}
 
 // Due to the complexities of global variable tracing, these will not generate warnings
 let unusedVariable = ""
@@ -504,3 +540,9 @@ func testVariablesBoundInPatterns() {
     break
   }
 }
+// Tests fix to SR-14646
+func testUselessCastWithInvalidParam(foo: Any?) -> Int {
+  class Foo { }
+  if let bar = foo as? Foo { return 42 } // expected-warning {{value 'bar' was defined but never used; consider replacing with boolean test}} {{6-16=}} {{20-23=is}}
+  else { return 54 }
+}

test/stmt/if_while_var.swift

@@ -59,8 +59,8 @@ if let x = foo() {
 
 var opt: Int? = .none
 
-if let x = opt {} // expected-warning {{value 'x' was defined but never used; consider replacing with boolean test}}
-if var x = opt {} // expected-warning {{value 'x' was defined but never used; consider replacing with boolean test}}
+if let x = opt {} // expected-warning {{value 'x' was defined but never used; consider replacing with boolean test}} {{4-12=}} {{15-15= != nil}}
+if var x = opt {} // expected-warning {{value 'x' was defined but never used; consider replacing with boolean test}} {{4-12=}} {{15-15= != nil}}
 
 // <rdar://problem/20800015> Fix error message for invalid if-let
 let someInteger = 1