do not reset current flow after processing finally block if it was unreachable (#11310)

* do not reset current flow after processing finally block if it was unreachable

* fix tests

Author: vladima

src/compiler/binder.ts

@@ -964,7 +964,11 @@ namespace ts {
                 currentFlow = preTryFlow;
                 bind(node.finallyBlock);
             }
-            currentFlow = finishFlowLabel(postFinallyLabel);
+            // if try statement has finally block and flow after finally block is unreachable - keep it
+            // otherwise use whatever flow was accumulated at postFinallyLabel
+            if (!node.finallyBlock || !(currentFlow.flags & FlowFlags.Unreachable)) {
+                currentFlow = finishFlowLabel(postFinallyLabel);
+            }
         }
 
         function bindSwitchStatement(node: SwitchStatement): void {

tests/baselines/reference/unreachableFlowAfterFinally.js

@@ -0,0 +1,27 @@
+//// [unreachableFlowAfterFinally.ts]
+
+function f() {
+    let x = 100;
+    try {
+        throw "WAT"
+    }
+    catch (e) {
+
+    }
+    finally {
+        return x;
+    }
+}
+
+//// [unreachableFlowAfterFinally.js]
+function f() {
+    var x = 100;
+    try {
+        throw "WAT";
+    }
+    catch (e) {
+    }
+    finally {
+        return x;
+    }
+}

tests/baselines/reference/unreachableFlowAfterFinally.symbols

@@ -0,0 +1,20 @@
+=== tests/cases/compiler/unreachableFlowAfterFinally.ts ===
+
+function f() {
+>f : Symbol(f, Decl(unreachableFlowAfterFinally.ts, 0, 0))
+
+    let x = 100;
+>x : Symbol(x, Decl(unreachableFlowAfterFinally.ts, 2, 7))
+
+    try {
+        throw "WAT"
+    }
+    catch (e) {
+>e : Symbol(e, Decl(unreachableFlowAfterFinally.ts, 6, 11))
+
+    }
+    finally {
+        return x;
+>x : Symbol(x, Decl(unreachableFlowAfterFinally.ts, 2, 7))
+    }
+}

tests/baselines/reference/unreachableFlowAfterFinally.types

@@ -0,0 +1,22 @@
+=== tests/cases/compiler/unreachableFlowAfterFinally.ts ===
+
+function f() {
+>f : () => number
+
+    let x = 100;
+>x : number
+>100 : 100
+
+    try {
+        throw "WAT"
+>"WAT" : "WAT"
+    }
+    catch (e) {
+>e : any
+
+    }
+    finally {
+        return x;
+>x : number
+    }
+}

tests/cases/compiler/unreachableFlowAfterFinally.ts

@@ -0,0 +1,14 @@
+// @noImplicitReturns: true
+
+function f() {
+    let x = 100;
+    try {
+        throw "WAT"
+    }
+    catch (e) {
+
+    }
+    finally {
+        return x;
+    }
+}