Sema: Fix false-positive var => let warning in VarUsageDeclChecker

Fixes <rdar://problem/60563962>.

Author: slavapestov

lib/Sema/MiscDiagnostics.cpp

@@ -2236,10 +2236,11 @@ class VarDeclUsageChecker : public ASTWalker {
   DiagnosticEngine &Diags;
   // Keep track of some information about a variable.
   enum {
-    RK_Read        = 1,      ///< Whether it was ever read.
-    RK_Written     = 2,      ///< Whether it was ever written or passed inout.
+    RK_Defined     = 1,      ///< Whether it was ever defined in this scope.
+    RK_Read        = 2,      ///< Whether it was ever read.
+    RK_Written     = 4,      ///< Whether it was ever written or passed inout.
 
-    RK_CaptureList = 4       ///< Var is an entry in a capture list.
+    RK_CaptureList = 8       ///< Var is an entry in a capture list.
   };
 
   /// These are all of the variables that we are tracking.  VarDecls get added
@@ -2280,7 +2281,7 @@ class VarDeclUsageChecker : public ASTWalker {
       if (FD->getAccessorKind() == AccessorKind::Set) {
         if (auto getter = dyn_cast<VarDecl>(FD->getStorage())) {
           auto arguments = FD->getParameters();
-          VarDecls[arguments->get(0)] = 0;
+          VarDecls[arguments->get(0)] = RK_Defined;
           AssociatedGetter = getter;
         }
       }
@@ -2291,9 +2292,9 @@ class VarDeclUsageChecker : public ASTWalker {
 
   VarDeclUsageChecker(VarDecl *vd) : Diags(vd->getASTContext().Diags) {
     // Track a specific VarDecl
-    VarDecls[vd] = 0;
+    VarDecls[vd] = RK_Defined;
     if (auto *childVd = vd->getCorrespondingCaseBodyVariable().getPtrOrNull()) {
-      VarDecls[childVd] = 0;
+      VarDecls[childVd] = RK_Defined;
     }
   }
 
@@ -2323,10 +2324,6 @@ class VarDeclUsageChecker : public ASTWalker {
     }
     return sawMutation;
   }
-    
-  bool isVarDeclEverWritten(VarDecl *VD) {
-    return (VarDecls[VD] & RK_Written) != 0;
-  }
 
   bool shouldTrackVarDecl(VarDecl *VD) {
     // If the variable is implicit, ignore it.
@@ -2355,9 +2352,7 @@ class VarDeclUsageChecker : public ASTWalker {
     auto *vd = dyn_cast<VarDecl>(D);
     if (!vd) return;
 
-    auto vdi = VarDecls.find(vd);
-    if (vdi != VarDecls.end())
-      vdi->second |= Flag;
+    VarDecls[vd] |= Flag;
   }
 
   void markBaseOfStorageUse(Expr *E, ConcreteDeclRef decl, unsigned flags);
@@ -2385,17 +2380,17 @@ class VarDeclUsageChecker : public ASTWalker {
           // that fact for better diagnostics.
           auto parentAsExpr = Parent.getAsExpr();
           if (parentAsExpr && isa<CaptureListExpr>(parentAsExpr))
-            return RK_CaptureList;
+            return RK_CaptureList | RK_Defined;
           // Otherwise, return none.
-          return 0;
+          return RK_Defined;
         }();
 
         if (!vd->isImplicit()) {
           if (auto *childVd =
                   vd->getCorrespondingCaseBodyVariable().getPtrOrNull()) {
             // Child vars are never in capture lists.
-            assert(defaultFlags == 0);
-            VarDecls[childVd] |= 0;
+            assert(defaultFlags == RK_Defined);
+            VarDecls[childVd] |= RK_Defined;
           }
         }
         VarDecls[vd] |= defaultFlags;
@@ -2437,7 +2432,7 @@ class VarDeclUsageChecker : public ASTWalker {
           if (!PBD) continue;
           for (auto idx : range(PBD->getNumPatternEntries())) {
             PBD->getPattern(idx)->forEachVariable([&](VarDecl *VD) {
-              VarDecls[VD] = RK_Read|RK_Written;
+              VarDecls[VD] = RK_Read|RK_Written|RK_Defined;
             });
           }
         } else if (node.is<Stmt *>()) {
@@ -2448,7 +2443,7 @@ class VarDeclUsageChecker : public ASTWalker {
           for (StmtConditionElement SCE : GS->getCond()) {
             if (auto pattern = SCE.getPatternOrNull()) {
               pattern->forEachVariable([&](VarDecl *VD) {
-                VarDecls[VD] = RK_Read|RK_Written;
+                VarDecls[VD] = RK_Read|RK_Written|RK_Defined;
               });
             }
           }
@@ -2507,7 +2502,7 @@ class VarDeclUsageChecker : public ASTWalker {
     // Make sure that we setup our case body variables.
     if (auto *caseStmt = dyn_cast<CaseStmt>(S)) {
       for (auto *vd : caseStmt->getCaseBodyVariablesOrEmptyArray()) {
-        VarDecls[vd] |= 0;
+        VarDecls[vd] |= RK_Defined;
       }
     }
 
@@ -2661,6 +2656,10 @@ VarDeclUsageChecker::~VarDeclUsageChecker() {
     unsigned access;
     std::tie(var, access) = p;
 
+    // If the variable was not defined in this scope, we can safely ignore it.
+    if (!(access & RK_Defined))
+      continue;
+
     if (auto *caseStmt =
             dyn_cast_or_null<CaseStmt>(var->getRecursiveParentPatternStmt())) {
       // Only diagnose VarDecls from the first CaseLabelItem in CaseStmts, as

test/SILGen/capture_order.swift

@@ -9,8 +9,6 @@ public func captureBeforeDefLet(amount: Int) -> () -> Int {
   }
   let closure = getter
   let modifiedAmount = amount // expected-note{{captured value declared here}}
-  // FIXME: Bogus warning!
-  // expected-warning@-2 {{initialization of immutable value 'modifiedAmount' was never used; consider replacing with assignment to '_' or removing it}}
   return closure
 }
 
@@ -21,8 +19,6 @@ public func captureBeforeDefVar(amount: Int) -> () -> Int {
   }
   let closure = incrementor
   var currentTotal = 0 // expected-note{{captured value declared here}}
-  // FIXME: Bogus warning!
-  // expected-warning@-2 {{variable 'currentTotal' was written to, but never read}}
   currentTotal = 1
   return closure
 }
@@ -33,8 +29,6 @@ public func captureBeforeDefWeakVar(obj: AnyObject) -> () -> AnyObject? {
   }
   let closure = getter
   weak var weakObj: AnyObject? = obj // expected-note{{captured value declared here}}
-  // FIXME: Bogus warning!
-  // expected-warning@-2 {{variable 'weakObj' was written to, but never read}}
   return closure
 }
 
@@ -44,8 +38,6 @@ public func captureBeforeDefUnownedLet(obj: AnyObject) -> () -> AnyObject? {
   }
   let closure = getter
   unowned let unownedObj: AnyObject = obj // expected-note{{captured value declared here}}
-  // FIXME: Bogus warning!
-  // expected-warning@-2 {{immutable value 'unownedObj' was never used; consider replacing with '_' or removing it}}
   return closure
 }
 
@@ -55,8 +47,6 @@ public func captureBeforeDefUnownedVar(obj: AnyObject) -> () -> AnyObject? {
   }
   let closure = getter
   unowned var unownedObj: AnyObject = obj // expected-note{{captured value declared here}}
-  // FIXME: Bogus warning!
-  // expected-warning@-2 {{variable 'unownedObj' was never used; consider replacing with '_' or removing it}}
   return closure
 }
 
@@ -122,8 +112,6 @@ func captureInClosure() {
   }
 
   var currentTotal = 0 // expected-note {{captured value declared here}}
-  // FIXME: Bogus warning!
-  // expected-warning@-2 {{initialization of variable 'currentTotal' was never used; consider replacing with assignment to '_' or removing it}}
 
   _ = x
 }
@@ -139,8 +127,6 @@ func sr3210_crash() {
 
   let b = 2 // expected-note {{captured value declared here}}
   // expected-warning@-1 {{code after 'return' will never be executed}}
-  // FIXME: Bogus warning!
-  // expected-warning@-3 {{initialization of immutable value 'b' was never used; consider replacing with assignment to '_' or removing it}}
 }
 
 func sr3210() {
@@ -149,8 +135,6 @@ func sr3210() {
   }
 
   let b = 2
-  // FIXME: Bogus warning!
-  // expected-warning@-2 {{initialization of immutable value 'b' was never used; consider replacing with assignment to '_' or removing it}}
 }
 
 class SR4812 {
@@ -193,8 +177,7 @@ class rdar40600800 {
 
     func innerFunction() {
       let closure = {
-      // FIXME: Bogus warning!
-      // expected-warning@-2 {{initialization of immutable value 'closure' was never used; consider replacing with assignment to '_' or removing it}}
+      // expected-warning@-1 {{initialization of immutable value 'closure' was never used; consider replacing with assignment to '_' or removing it}}
         callback() // expected-note {{captured here}}
       }
     }

test/decl/var/usage.swift

@@ -434,4 +434,15 @@ func testLocalFunc() {
     _ = notMutatedVar
     mutatedVar = 1
   }
-}
+}
+
+// False positive "'var' was never mutated" warning - rdar://60563962
+func testForwardReferenceCapture() {
+  func innerFunc() {
+    x = 10
+  }
+
+  var x: Int = 1
+  innerFunc()
+  print(x)
+}