check that default clause is non-empty in reachability checks

Author: vladima

src/compiler/binder.ts

@@ -912,8 +912,8 @@ namespace ts {
             preSwitchCaseFlow = currentFlow;
             bind(node.caseBlock);
             addAntecedent(postSwitchLabel, currentFlow);
-            const hasDefault = forEach(node.caseBlock.clauses, c => c.kind === SyntaxKind.DefaultClause);
-            if (!hasDefault) {
+            const hasNonEmptyDefault = forEach(node.caseBlock.clauses, c => c.kind === SyntaxKind.DefaultClause && c.statements.length);
+            if (!hasNonEmptyDefault) {
                 addAntecedent(postSwitchLabel, preSwitchCaseFlow);
             }
             currentBreakTarget = saveBreakTarget;

tests/baselines/reference/reachabilityCheckWithEmptyDefault.js

@@ -0,0 +1,18 @@
+//// [reachabilityCheckWithEmptyDefault.ts]
+declare function print(s: string): void;
+function foo(x: any) {
+	switch(x) {
+		case 1: return;
+		default:
+	}
+	print('1');
+}
+
+//// [reachabilityCheckWithEmptyDefault.js]
+function foo(x) {
+    switch (x) {
+        case 1: return;
+        default:
+    }
+    print('1');
+}

tests/baselines/reference/reachabilityCheckWithEmptyDefault.symbols

@@ -0,0 +1,18 @@
+=== tests/cases/compiler/reachabilityCheckWithEmptyDefault.ts ===
+declare function print(s: string): void;
+>print : Symbol(print, Decl(reachabilityCheckWithEmptyDefault.ts, 0, 0))
+>s : Symbol(s, Decl(reachabilityCheckWithEmptyDefault.ts, 0, 23))
+
+function foo(x: any) {
+>foo : Symbol(foo, Decl(reachabilityCheckWithEmptyDefault.ts, 0, 40))
+>x : Symbol(x, Decl(reachabilityCheckWithEmptyDefault.ts, 1, 13))
+
+	switch(x) {
+>x : Symbol(x, Decl(reachabilityCheckWithEmptyDefault.ts, 1, 13))
+
+		case 1: return;
+		default:
+	}
+	print('1');
+>print : Symbol(print, Decl(reachabilityCheckWithEmptyDefault.ts, 0, 0))
+}

tests/baselines/reference/reachabilityCheckWithEmptyDefault.types

@@ -0,0 +1,22 @@
+=== tests/cases/compiler/reachabilityCheckWithEmptyDefault.ts ===
+declare function print(s: string): void;
+>print : (s: string) => void
+>s : string
+
+function foo(x: any) {
+>foo : (x: any) => void
+>x : any
+
+	switch(x) {
+>x : any
+
+		case 1: return;
+>1 : number
+
+		default:
+	}
+	print('1');
+>print('1') : void
+>print : (s: string) => void
+>'1' : string
+}

tests/cases/compiler/reachabilityCheckWithEmptyDefault.ts

@@ -0,0 +1,8 @@
+declare function print(s: string): void;
+function foo(x: any) {
+	switch(x) {
+		case 1: return;
+		default:
+	}
+	print('1');
+}