Properly analyze switch statement bypass control flow (microsoft#35087)

* Properly analyze switch statement bypass control flow

* Add regression test

* Accept new baselines

Author: ahejlsberg

src/compiler/checker.ts

@@ -19333,7 +19333,7 @@ namespace ts {
                     }
                 }
                 if (bypassFlow) {
-                    const flowType = getTypeAtFlowNode(bypassFlow.antecedent);
+                    const flowType = getTypeAtFlowNode(bypassFlow);
                     const type = getTypeFromFlowType(flowType);
                     // If the bypass flow contributes a type we haven't seen yet and the switch statement
                     // isn't exhaustive, process the bypass flow type. Since exhaustiveness checks increase

tests/baselines/reference/exhaustiveSwitchStatements1.errors.txt

@@ -1,7 +1,8 @@
 tests/cases/conformance/controlFlow/exhaustiveSwitchStatements1.ts(7,9): error TS7027: Unreachable code detected.
+tests/cases/conformance/controlFlow/exhaustiveSwitchStatements1.ts(235,5): error TS2367: This condition will always return 'false' since the types '"a" | "b"' and '"c"' have no overlap.
 
 
-==== tests/cases/conformance/controlFlow/exhaustiveSwitchStatements1.ts (1 errors) ====
+==== tests/cases/conformance/controlFlow/exhaustiveSwitchStatements1.ts (2 errors) ====
     function f1(x: 1 | 2): string {
         if (!!true) {
             switch (x) {
@@ -225,4 +226,22 @@ tests/cases/conformance/controlFlow/exhaustiveSwitchStatements1.ts(7,9): error T
             }
         }
     }
+    
+    // Repro from #35070
+    
+    type O = {
+        a: number,
+        b: number
+    };
+    type K = keyof O | 'c';
+    function ff(o: O, k: K) {
+        switch(k) {
+            case 'c':
+                k = 'a';
+        }
+        k === 'c';  // Error
+        ~~~~~~~~~
+!!! error TS2367: This condition will always return 'false' since the types '"a" | "b"' and '"c"' have no overlap.
+        return o[k];
+    }
 

tests/baselines/reference/exhaustiveSwitchStatements1.js

@@ -220,6 +220,22 @@ function foo() {
         }
     }
 }
+
+// Repro from #35070
+
+type O = {
+    a: number,
+    b: number
+};
+type K = keyof O | 'c';
+function ff(o: O, k: K) {
+    switch(k) {
+        case 'c':
+            k = 'a';
+    }
+    k === 'c';  // Error
+    return o[k];
+}
 
 
 //// [exhaustiveSwitchStatements1.js]
@@ -429,6 +445,14 @@ function foo() {
         }
     }
 }
+function ff(o, k) {
+    switch (k) {
+        case 'c':
+            k = 'a';
+    }
+    k === 'c'; // Error
+    return o[k];
+}
 
 
 //// [exhaustiveSwitchStatements1.d.ts]
@@ -494,3 +518,9 @@ declare const zoo: {
 } | undefined;
 declare function expression(): Animal;
 declare function foo(): void;
+declare type O = {
+    a: number;
+    b: number;
+};
+declare type K = keyof O | 'c';
+declare function ff(o: O, k: K): number;

tests/baselines/reference/exhaustiveSwitchStatements1.symbols

@@ -565,3 +565,41 @@ function foo() {
     }
 }
 
+// Repro from #35070
+
+type O = {
+>O : Symbol(O, Decl(exhaustiveSwitchStatements1.ts, 220, 1))
+
+    a: number,
+>a : Symbol(a, Decl(exhaustiveSwitchStatements1.ts, 224, 10))
+
+    b: number
+>b : Symbol(b, Decl(exhaustiveSwitchStatements1.ts, 225, 14))
+
+};
+type K = keyof O | 'c';
+>K : Symbol(K, Decl(exhaustiveSwitchStatements1.ts, 227, 2))
+>O : Symbol(O, Decl(exhaustiveSwitchStatements1.ts, 220, 1))
+
+function ff(o: O, k: K) {
+>ff : Symbol(ff, Decl(exhaustiveSwitchStatements1.ts, 228, 23))
+>o : Symbol(o, Decl(exhaustiveSwitchStatements1.ts, 229, 12))
+>O : Symbol(O, Decl(exhaustiveSwitchStatements1.ts, 220, 1))
+>k : Symbol(k, Decl(exhaustiveSwitchStatements1.ts, 229, 17))
+>K : Symbol(K, Decl(exhaustiveSwitchStatements1.ts, 227, 2))
+
+    switch(k) {
+>k : Symbol(k, Decl(exhaustiveSwitchStatements1.ts, 229, 17))
+
+        case 'c':
+            k = 'a';
+>k : Symbol(k, Decl(exhaustiveSwitchStatements1.ts, 229, 17))
+    }
+    k === 'c';  // Error
+>k : Symbol(k, Decl(exhaustiveSwitchStatements1.ts, 229, 17))
+
+    return o[k];
+>o : Symbol(o, Decl(exhaustiveSwitchStatements1.ts, 229, 12))
+>k : Symbol(k, Decl(exhaustiveSwitchStatements1.ts, 229, 17))
+}
+

tests/baselines/reference/exhaustiveSwitchStatements1.types

@@ -662,3 +662,45 @@ function foo() {
     }
 }
 
+// Repro from #35070
+
+type O = {
+>O : O
+
+    a: number,
+>a : number
+
+    b: number
+>b : number
+
+};
+type K = keyof O | 'c';
+>K : K
+
+function ff(o: O, k: K) {
+>ff : (o: O, k: K) => number
+>o : O
+>k : K
+
+    switch(k) {
+>k : K
+
+        case 'c':
+>'c' : "c"
+
+            k = 'a';
+>k = 'a' : "a"
+>k : K
+>'a' : "a"
+    }
+    k === 'c';  // Error
+>k === 'c' : boolean
+>k : "a" | "b"
+>'c' : "c"
+
+    return o[k];
+>o[k] : number
+>o : O
+>k : "a" | "b"
+}
+

tests/cases/conformance/controlFlow/exhaustiveSwitchStatements1.ts

@@ -223,3 +223,19 @@ function foo() {
         }
     }
 }
+
+// Repro from #35070
+
+type O = {
+    a: number,
+    b: number
+};
+type K = keyof O | 'c';
+function ff(o: O, k: K) {
+    switch(k) {
+        case 'c':
+            k = 'a';
+    }
+    k === 'c';  // Error
+    return o[k];
+}