[csdiag] offer a fix-it to turn a stored property into a computed property if needed

Author: theblixguy

include/swift/AST/DiagnosticsSema.def

@@ -1522,6 +1522,8 @@ ERROR(extension_specialization,none,
       "type %0 with constraints specified by a 'where' clause", (Identifier))
 ERROR(extension_stored_property,none,
       "extensions must not contain stored properties", ())
+NOTE(extension_stored_property_fixit,none,
+     "Remove '=' to make %0 a computed property", (Identifier))
 ERROR(extension_nongeneric_trailing_where,none,
       "trailing 'where' clause for extension of non-generic type %0",
       (DeclName))

lib/Sema/CSDiag.cpp

@@ -2325,6 +2325,51 @@ bool FailureDiagnosis::diagnoseContextualConversionError(
       diagnose(expr->getLoc(), diag::missing_nullary_call, srcFT->getResult())
         .highlight(expr->getSourceRange())
         .fixItInsertAfter(expr->getEndLoc(), "()");
+
+      // It is possible that we're looking at a stored property being
+      // initialized with a closure. Something like:
+      //
+      // var foo: Int = { return 0 }
+      //
+      // Let's offer another fix-it to remove the '=' to turn the stored
+      // property into a computed property. If the variable is immutable, then
+      // replace the 'let' with a 'var'
+
+      // First, check if the variable is declared top level or not. If it is
+      // not, then it means we're inside a decl like a class or an extension.
+      PatternBindingDecl *PBD = nullptr;
+
+      if (auto TLCD = dyn_cast<TopLevelCodeDecl>(CS.DC)) {
+        if (TLCD->getBody()->isImplicit()) {
+          if (auto decl = TLCD->getBody()->getElement(0).dyn_cast<Decl *>()) {
+            if (auto binding = dyn_cast<PatternBindingDecl>(decl)) {
+              PBD = binding;
+            }
+          }
+        }
+      } else if (auto PBI = dyn_cast<PatternBindingInitializer>(CS.DC)) {
+        PBD = PBI->getBinding();
+      }
+
+      if (PBD) {
+        if (auto VD = PBD->getSingleVar()) {
+          auto entry = PBD->getPatternEntryForVarDecl(VD);
+
+          if (!VD->isStatic() &&
+              !VD->getAttrs().getAttribute<DynamicReplacementAttr>() &&
+              entry.getInit() && isa<ClosureExpr>(entry.getInit())) {
+            auto diag = CS.TC.diagnose(expr->getLoc(),
+                                       diag::extension_stored_property_fixit,
+                                       VD->getName());
+            diag.fixItRemove(entry.getEqualLoc());
+
+            if (VD->isLet()) {
+              diag.fixItReplace(PBD->getStartLoc(), getTokenText(tok::kw_var));
+            }
+          }
+        }
+      }
+
       return true;
     }
   }

test/decl/var/properties.swift

@@ -1277,3 +1277,32 @@ let sr8811b: Never = fatalError() // Ok
 let sr8811c = (16, fatalError()) // expected-warning {{constant 'sr8811c' inferred to have type '(Int, Never)', which contains an enum with no cases}} expected-note {{add an explicit type annotation to silence this warning}}
 
 let sr8811d: (Int, Never) = (16, fatalError()) // Ok
+
+// SR-9267
+
+class SR_9267 {}
+extension SR_9267 {
+  var foo: String = { // expected-error {{extensions must not contain stored properties}} // expected-error {{function produces expected type 'String'; did you mean to call it with '()'?}} // expected-note {{Remove '=' to make 'foo' a computed property}}{{19-21=}}
+    return "Hello"
+  }
+}
+
+enum SR_9267_E {
+  var SR_9267_prop: String = { // expected-error {{enums must not contain stored properties}} // expected-error {{function produces expected type 'String'; did you mean to call it with '()'?}} // expected-note {{Remove '=' to make 'SR_9267_prop' a computed property}}{{28-30=}}
+    return "Hello"
+  }
+}
+
+var SR_9267_prop_1: Int = { // expected-error {{function produces expected type 'Int'; did you mean to call it with '()'?}} // expected-note {{Remove '=' to make 'SR_9267_prop_1' a computed property}}{{25-27=}}
+  return 0
+}
+
+class SR_9267_C {
+  var SR_9267_prop_2: String = { // expected-error {{function produces expected type 'String'; did you mean to call it with '()'?}} // expected-note {{Remove '=' to make 'SR_9267_prop_2' a computed property}}{{30-32=}}
+    return "Hello"
+  }
+}
+
+class SR_9267_C2 {
+  let SR_9267_prop_3: Int = { return 0 } // expected-error {{function produces expected type 'Int'; did you mean to call it with '()'?}} // expected-note {{Remove '=' to make 'SR_9267_prop_3' a computed property}}{{3-6=var}}{{27-29=}}
+}