Correctly handle nested switches

Author: RyanCavanaugh

src/compiler/checker.ts

@@ -25258,9 +25258,14 @@ namespace ts {
             //         if (true) x; // <- bad (note: need to walk to parent)
             // }
             if (container.kind === SyntaxKind.CaseBlock) {
-                const usageCaseBlock = getAncestor(node, SyntaxKind.CaseClause);
-                if (usageCaseBlock) {
-                    if (usageCaseBlock.pos > symbol.valueDeclaration.pos) {
+                let usageCaseClause = getAncestor(node, SyntaxKind.CaseClause);
+                if (usageCaseClause) {
+                    // Walk up until we're at the same level as the declaring block
+                    while (usageCaseClause.parent !== container) {
+                        usageCaseClause = usageCaseClause!.parent;
+                    }
+
+                    if (usageCaseClause.pos > symbol.valueDeclaration.pos) {
                         error(node, Diagnostics.Variable_0_is_declared_in_a_prior_case_block, symbolToString(symbol));
                     }
                 }

tests/baselines/reference/switchCaseTdz.errors.txt

@@ -19,10 +19,9 @@ tests/cases/compiler/switchCaseTdz.ts(46,13): error TS2837: Variable 'z' is decl
 tests/cases/compiler/switchCaseTdz.ts(50,13): error TS2837: Variable 'x' is declared in a prior case block.
 tests/cases/compiler/switchCaseTdz.ts(51,13): error TS2837: Variable 'y' is declared in a prior case block.
 tests/cases/compiler/switchCaseTdz.ts(52,13): error TS2837: Variable 'z' is declared in a prior case block.
-tests/cases/compiler/switchCaseTdz.ts(64,17): error TS2837: Variable 'x' is declared in a prior case block.
 
 
-==== tests/cases/compiler/switchCaseTdz.ts (22 errors) ====
+==== tests/cases/compiler/switchCaseTdz.ts (21 errors) ====
     switch (1 + 1) {
         case -1:
             x;
@@ -132,7 +131,5 @@ tests/cases/compiler/switchCaseTdz.ts(64,17): error TS2837: Variable 'x' is decl
                 case 2:
                     // Legal
                     x;
-                    ~
-!!! error TS2837: Variable 'x' is declared in a prior case block.
             }
     }