Merge pull request microsoft#7329 from Microsoft/allowFallFromLastCase

allow fallthrough from the last case of the switch

Author: vladima

src/compiler/binder.ts

@@ -708,10 +708,14 @@ namespace ts {
  function bindCaseBlock(n: CaseBlock): void {
  const startState = currentReachabilityState;
 
- for (const clause of n.clauses) {
+ for (let i = 0; i < n.clauses.length; i++) {
+ const clause = n.clauses[i];
  currentReachabilityState = startState;
  bind(clause);
- if (clause.statements.length && currentReachabilityState === Reachability.Reachable && options.noFallthroughCasesInSwitch) {
+ if (clause.statements.length &&
+ i !== n.clauses.length - 1 && // allow fallthrough from the last case
+ currentReachabilityState === Reachability.Reachable &&
+ options.noFallthroughCasesInSwitch) {
  errorOnFirstToken(clause, Diagnostics.Fallthrough_case_in_switch);
  }
  }

tests/baselines/reference/fallFromLastCase1.js

@@ -0,0 +1,44 @@
+//// [fallFromLastCase1.ts]
+
+declare function use(a: string);
+
+function foo1(a: number) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ case 2:
+ use("2");
+ }
+}
+
+
+function foo2(a: number) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ default:
+ use("2");
+ }
+}
+
+//// [fallFromLastCase1.js]
+function foo1(a) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ case 2:
+ use("2");
+ }
+}
+function foo2(a) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ default:
+ use("2");
+ }
+}

tests/baselines/reference/fallFromLastCase1.symbols

@@ -0,0 +1,42 @@
+=== tests/cases/compiler/fallFromLastCase1.ts ===
+
+declare function use(a: string);
+>use : Symbol(use, Decl(fallFromLastCase1.ts, 0, 0))
+>a : Symbol(a, Decl(fallFromLastCase1.ts, 1, 21))
+
+function foo1(a: number) {
+>foo1 : Symbol(foo1, Decl(fallFromLastCase1.ts, 1, 32))
+>a : Symbol(a, Decl(fallFromLastCase1.ts, 3, 14))
+
+ switch (a) {
+>a : Symbol(a, Decl(fallFromLastCase1.ts, 3, 14))
+
+ case 1:
+ use("1");
+>use : Symbol(use, Decl(fallFromLastCase1.ts, 0, 0))
+
+ break;
+ case 2:
+ use("2");
+>use : Symbol(use, Decl(fallFromLastCase1.ts, 0, 0))
+ }
+}
+
+
+function foo2(a: number) {
+>foo2 : Symbol(foo2, Decl(fallFromLastCase1.ts, 11, 1))
+>a : Symbol(a, Decl(fallFromLastCase1.ts, 14, 14))
+
+ switch (a) {
+>a : Symbol(a, Decl(fallFromLastCase1.ts, 14, 14))
+
+ case 1:
+ use("1");
+>use : Symbol(use, Decl(fallFromLastCase1.ts, 0, 0))
+
+ break;
+ default:
+ use("2");
+>use : Symbol(use, Decl(fallFromLastCase1.ts, 0, 0))
+ }
+}

tests/baselines/reference/fallFromLastCase1.types

@@ -0,0 +1,56 @@
+=== tests/cases/compiler/fallFromLastCase1.ts ===
+
+declare function use(a: string);
+>use : (a: string) => any
+>a : string
+
+function foo1(a: number) {
+>foo1 : (a: number) => void
+>a : number
+
+ switch (a) {
+>a : number
+
+ case 1:
+>1 : number
+
+ use("1");
+>use("1") : any
+>use : (a: string) => any
+>"1" : string
+
+ break;
+ case 2:
+>2 : number
+
+ use("2");
+>use("2") : any
+>use : (a: string) => any
+>"2" : string
+ }
+}
+
+
+function foo2(a: number) {
+>foo2 : (a: number) => void
+>a : number
+
+ switch (a) {
+>a : number
+
+ case 1:
+>1 : number
+
+ use("1");
+>use("1") : any
+>use : (a: string) => any
+>"1" : string
+
+ break;
+ default:
+ use("2");
+>use("2") : any
+>use : (a: string) => any
+>"2" : string
+ }
+}

tests/baselines/reference/fallFromLastCase2.errors.txt

@@ -0,0 +1,36 @@
+tests/cases/compiler/fallFromLastCase2.ts(9,9): error TS7029: Fallthrough case in switch.
+tests/cases/compiler/fallFromLastCase2.ts(22,9): error TS7029: Fallthrough case in switch.
+
+
+==== tests/cases/compiler/fallFromLastCase2.ts (2 errors) ====
+ 
+ declare function use(a: string);
+ 
+ function foo1(a: number) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ case 2:
+ ~~~~
+!!! error TS7029: Fallthrough case in switch.
+ use("2");
+ case 3:
+ use("3");
+ }
+ }
+ 
+ 
+ function foo2(a: number) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ default:
+ ~~~~~~~
+!!! error TS7029: Fallthrough case in switch.
+ use("2");
+ case 2:
+ use("3");
+ }
+ }

tests/baselines/reference/fallFromLastCase2.js

@@ -0,0 +1,52 @@
+//// [fallFromLastCase2.ts]
+
+declare function use(a: string);
+
+function foo1(a: number) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ case 2:
+ use("2");
+ case 3:
+ use("3");
+ }
+}
+
+
+function foo2(a: number) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ default:
+ use("2");
+ case 2:
+ use("3");
+ }
+}
+
+//// [fallFromLastCase2.js]
+function foo1(a) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ case 2:
+ use("2");
+ case 3:
+ use("3");
+ }
+}
+function foo2(a) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ default:
+ use("2");
+ case 2:
+ use("3");
+ }
+}

tests/cases/compiler/fallFromLastCase1.ts

@@ -0,0 +1,24 @@
+// @noFallthroughCasesInSwitch: true
+
+declare function use(a: string);
+
+function foo1(a: number) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ case 2:
+ use("2");
+ }
+}
+
+
+function foo2(a: number) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ default:
+ use("2");
+ }
+}

tests/cases/compiler/fallFromLastCase2.ts

@@ -0,0 +1,28 @@
+// @noFallthroughCasesInSwitch: true
+
+declare function use(a: string);
+
+function foo1(a: number) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ case 2:
+ use("2");
+ case 3:
+ use("3");
+ }
+}
+
+
+function foo2(a: number) {
+ switch (a) {
+ case 1:
+ use("1");
+ break;
+ default:
+ use("2");
+ case 2:
+ use("3");
+ }
+}