Remove the ability to map back from a ParamDecl to its enclosing Pattern. This

is used by precisely one thing (producing a warning in a scenario that is obsolete
because we deprecated the entire thing), so the complexity isn't worth it anymore.

include/swift/AST/Decl.h

@@ -4007,7 +4007,7 @@ public:
 /// VarDecl - 'var' and 'let' declarations.
 class VarDecl : public AbstractStorageDecl {
 protected:
-  llvm::PointerUnion3<PatternBindingDecl*, Pattern*, Stmt*> ParentPattern;
+  llvm::PointerUnion<PatternBindingDecl*, Stmt*> ParentPattern;
 
   VarDecl(DeclKind Kind, bool IsStatic, bool IsLet, SourceLoc NameLoc,
           Identifier Name, Type Ty, DeclContext *DC)
@@ -4186,13 +4186,6 @@ public:
     return SourceRange(ArgumentNameLoc, getNameLoc());
   }
 
-  Pattern *getParamParentPattern() const {
-    return ParentPattern.dyn_cast<Pattern *>();
-  }
-  void setParamParentPattern(Pattern *Pat) {
-    ParentPattern = Pat;
-  }
-
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { 
     return D->getKind() == DeclKind::Param;

lib/AST/Builtins.cpp

@@ -157,8 +157,6 @@ getBuiltinFunction(Identifier Id, ArrayRef<Type> argTypes, Type ResType,
     Pattern *Pat = new (Context) NamedPattern(PD, /*implicit=*/true);
     Pat = new (Context) TypedPattern(Pat, TypeLoc::withoutLoc(argType),
                                      /*implicit=*/true);
-    PD->setParamParentPattern(Pat);
-
     ParamPatternElts.push_back(TuplePatternElt(Pat));
   }
 
@@ -228,7 +226,6 @@ getBuiltinGenericFunction(Identifier Id,
     Pattern *Pat = new (Context) NamedPattern(PD, /*implicit=*/true);
     Pat = new (Context) TypedPattern(Pat,
             TypeLoc::withoutLoc(ArgTupleElt.getType()), /*implicit=*/true);
-    PD->setParamParentPattern(Pat);
 
     ParamPatternElts.push_back(TuplePatternElt(Pat));
   }

lib/AST/Decl.cpp

@@ -3154,11 +3154,7 @@ SourceRange VarDecl::getSourceRange() const {
 }
 
 SourceRange VarDecl::getTypeSourceRangeForDiagnostics() const {
-  Pattern *Pat = nullptr;
-  if (ParentPattern.is<Pattern*>())
-    Pat = ParentPattern.dyn_cast<Pattern *>();
-  else
-    Pat = getParentPattern();
+  Pattern *Pat = getParentPattern();
   
   if (!Pat || Pat->isImplicit())
     return getSourceRange();

lib/AST/Pattern.cpp

@@ -310,7 +310,6 @@ static Pattern *buildImplicitLetParameter(ASTContext &ctx, Identifier name,
   P->setType(tyLoc.getType());
   P = new (ctx) TypedPattern(P, tyLoc, /*Implicit=*/true);
   P->setType(tyLoc.getType());
-  paramDecl->setParamParentPattern(P);
   return P;
 }
 

lib/Parse/ParsePattern.cpp

@@ -392,9 +392,6 @@ mapParsedParameters(Parser &parser,
       bool isLet = specifierKind == Parser::ParsedParameter::Let;
       param = new (ctx) VarPattern(letVarInOutLoc, isLet, param);
     }
-
-    if (var)
-      var->setParamParentPattern(param);
     return param;
   };
 

lib/Sema/MiscDiagnostics.cpp

@@ -1492,17 +1492,7 @@ VarDeclUsageChecker::~VarDeclUsageChecker() {
       }
 
       // If this is a parameter explicitly marked 'var', remove it.
-      if (auto *param = dyn_cast<ParamDecl>(var))
-        if (auto *pattern = param->getParamParentPattern())
-          if (auto *vp = dyn_cast<VarPattern>(pattern)) {
-            TC.diagnose(var->getLoc(), diag::variable_never_mutated,
-                        var->getName(), /*param*/1)
-              .fixItRemove(vp->getLoc());
-            continue;
-          }
-      
       unsigned varKind = isa<ParamDecl>(var);
-      // FIXME: fixit when we can find a pattern binding.
       if (FixItLoc.isInvalid())
         TC.diagnose(var->getLoc(), diag::variable_never_mutated,
                     var->getName(), varKind);

test/FixCode/fixits-apply.swift.result

@@ -38,7 +38,7 @@ func foo() -> Int {
   }
 }
 
-func goo(e : ErrorType) {}
+func goo(var e : ErrorType) {}
 
 struct Test1 : OptionSetType {
   init(rawValue: Int) {}