[Sema] Rename bindSwitchCasePatternVars -> diagnoseCaseVarMutabilityMismatch

Now that we wire up the parents up-front, this no longer needs to
set the parents. As such, remove the logic and rename to reflect the
fact that it now just diagnoses mutability mismatches.

Author: hamishknight

lib/Sema/CSSyntacticElement.cpp

@@ -2005,7 +2005,7 @@ class SyntacticElementSolutionApplication
       }
     }
 
-    bindSwitchCasePatternVars(context.getAsDeclContext(), caseStmt);
+    diagnoseCaseVarMutabilityMismatch(context.getAsDeclContext(), caseStmt);
 
     for (auto *expected : caseStmt->getCaseBodyVariables()) {
       assert(expected->hasName());

lib/Sema/TypeCheckStmt.cpp

@@ -1581,9 +1581,7 @@ class StmtChecker : public StmtVisitor<StmtChecker, Stmt*> {
 
     // First pass: check all of the bindings.
     for (auto *caseBlock : make_range(casesBegin, casesEnd)) {
-      // Bind all of the pattern variables together so we can follow the
-      // "parent" pointers later on.
-      bindSwitchCasePatternVars(DC, caseBlock);
+      diagnoseCaseVarMutabilityMismatch(DC, caseBlock);
 
       auto caseLabelItemArray = caseBlock->getMutableCaseLabelItems();
       for (auto &labelItem : caseLabelItemArray) {
@@ -3238,7 +3236,8 @@ void swift::checkUnknownAttrRestrictions(
   }
 }
 
-void swift::bindSwitchCasePatternVars(DeclContext *dc, CaseStmt *caseStmt) {
+void swift::diagnoseCaseVarMutabilityMismatch(DeclContext *dc,
+                                              CaseStmt *caseStmt) {
   llvm::SmallDenseMap<Identifier, std::pair<VarDecl *, bool>, 4> latestVars;
   auto recordVar = [&](Pattern *pattern, VarDecl *var) {
     if (!var->hasName())
@@ -3248,16 +3247,10 @@ void swift::bindSwitchCasePatternVars(DeclContext *dc, CaseStmt *caseStmt) {
     // parent of this new variable.
     auto &entry = latestVars[var->getName()];
     if (entry.first) {
-      assert(!var->getParentVarDecl() ||
-             var->getParentVarDecl() == entry.first);
-      var->setParentVarDecl(entry.first);
-
       // Check for a mutability mismatch.
-      if (pattern && entry.second != var->isLet()) {
+      if (entry.second != var->isLet()) {
         // Find the original declaration.
-        auto initialCaseVarDecl = entry.first;
-        while (auto parentVar = initialCaseVarDecl->getParentVarDecl())
-          initialCaseVarDecl = parentVar;
+        auto initialCaseVarDecl = entry.first->getCanonicalVarDecl();
 
         auto diag = var->diagnose(diag::mutability_mismatch_multiple_pattern_list,
                                   var->isLet(), initialCaseVarDecl->isLet());
@@ -3268,10 +3261,10 @@ void swift::bindSwitchCasePatternVars(DeclContext *dc, CaseStmt *caseStmt) {
             if (VP->getSingleVar() == var)
               foundVP = VP;
         });
-        if (foundVP)
+        if (foundVP) {
           diag.fixItReplace(foundVP->getLoc(),
                             initialCaseVarDecl->isLet() ? "let" : "var");
-
+        }
         var->setInvalid();
         initialCaseVarDecl->setInvalid();
       }
@@ -3283,8 +3276,6 @@ void swift::bindSwitchCasePatternVars(DeclContext *dc, CaseStmt *caseStmt) {
     entry.first = var;
   };
 
-  // Wire up the parent var decls for each variable that occurs within
-  // the patterns of each case item. in source order.
   for (auto &caseItem : caseStmt->getMutableCaseLabelItems()) {
     // Resolve the pattern.
     auto *pattern = caseItem.getPattern();
@@ -3300,11 +3291,6 @@ void swift::bindSwitchCasePatternVars(DeclContext *dc, CaseStmt *caseStmt) {
       recordVar(pattern, var);
     });
   }
-
-  // Wire up the case body variables to the latest patterns.
-  for (auto bodyVar : caseStmt->getCaseBodyVariables()) {
-    recordVar(nullptr, bodyVar);
-  }
 }
 
 FuncDecl *TypeChecker::getForEachIteratorNextFunction(

lib/Sema/TypeChecker.h

@@ -1416,26 +1416,9 @@ bool checkFallthroughStmt(FallthroughStmt *stmt);
 void checkUnknownAttrRestrictions(
     ASTContext &ctx, CaseStmt *caseBlock, bool &limitExhaustivityChecks);
 
-/// Bind all of the pattern variables that occur within a case statement and
-/// all of its case items to their "parent" pattern variables, forming chains
-/// of variables with the same name.
-///
-/// Given a case such as:
-/// \code
-/// case .a(let x), .b(let x), .c(let x):
-/// \endcode
-///
-/// Each case item contains a (different) pattern variable named.
-/// "x". This function will set the "parent" variable of the
-/// second and third "x" variables to the "x" variable immediately
-/// to its left. A fourth "x" will be the body case variable,
-/// whose parent will be set to the "x" within the final case
-/// item.
-///
-/// Each of the "x" variables must eventually have the same type, and agree on
-/// let vs. var. This function does not perform any of that validation, leaving
-/// it to later stages.
-void bindSwitchCasePatternVars(DeclContext *dc, CaseStmt *stmt);
+/// Diagnoses any mutability mismatches for any same-named variables bound by
+/// given CaseStmt.
+void diagnoseCaseVarMutabilityMismatch(DeclContext *dc, CaseStmt *stmt);
 
 /// If \p attr was added by an access note, wraps the error in
 /// \c diag::wrap_invalid_attr_added_by_access_note and limits it as an access