[Sema] Offer 'is' replacement for unused 'if let' expression when the operand is optional

Author: mininny

lib/Sema/MiscDiagnostics.cpp

@@ -2893,7 +2893,20 @@ VarDeclUsageChecker::~VarDeclUsageChecker() {
                       !initExpr->isImplicit()) {
                     noParens = isIsTest = 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)) {
+                    if (auto ccExpr = dyn_cast<ConditionalCheckedCastExpr>(
+                            oeExpr->getSubExpr())) {
+                      if (!ccExpr->isImplicit()) {
+                        initExpr = ccExpr;
+                        noParens = isIsTest = true;
+                      }
+                    }
+                  }
+
                   auto diagIF = Diags.diagnose(var->getLoc(),
                                                diag::pbd_never_used_stmtcond,
                                             var->getName());

test/decl/var/usage.swift

@@ -330,6 +330,11 @@ 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-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}}
+  }
+
   // SR-1112
 
   let xxx: Int? = 0
@@ -356,7 +361,7 @@ 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 +509,9 @@ func testVariablesBoundInPatterns() {
     break
   }
 }
+// Tests fix to SR-1464
+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