Add never helper function (microsoft#18287)

Andy · web-flow · commit 409d6597ebde · 2017-09-08T14:22:44.000-07:00
* Add `never` helper function

* Move to Debug.assertNever, keep old messages
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -1687,7 +1687,7 @@ namespace ts {
                     undefined;
             }
             else {
-                Debug.fail("Unknown entity name kind.");
+                Debug.assertNever(name, "Unknown entity name kind.");
             }
             Debug.assert((getCheckFlags(symbol) & CheckFlags.Instantiated) === 0, "Should never get an instantiated symbol here.");
             return (symbol.flags & meaning) || dontResolveAlias ? symbol : resolveAlias(symbol);
@@ -16357,7 +16357,7 @@ namespace ts {
                     // This code-path is called by language service
                     return resolveStatelessJsxOpeningLikeElement(<JsxOpeningLikeElement>node, checkExpression((<JsxOpeningLikeElement>node).tagName), candidatesOutArray);
             }
-            Debug.fail("Branch in 'resolveSignature' should be unreachable.");
+            Debug.assertNever(node, "Branch in 'resolveSignature' should be unreachable.");
         }
 
         /**
@@ -24535,7 +24535,7 @@ namespace ts {
                     currentKind = SetAccessor;
                 }
                 else {
-                    Debug.fail("Unexpected syntax kind:" + (<Node>prop).kind);
+                    Debug.assertNever(prop, "Unexpected syntax kind:" + (<Node>prop).kind);
                 }
 
                 const effectiveName = getPropertyNameForPropertyNameNode(name);

Original file line number	Diff line number	Diff line change
`@@ -1687,7 +1687,7 @@ namespace ts {`
`1687`	`1687`	`undefined;`
`1688`	`1688`	`}`
`1689`	`1689`	`else {`
`1690`		`- Debug.fail("Unknown entity name kind.");`
	`1690`	`+ Debug.assertNever(name, "Unknown entity name kind.");`
`1691`	`1691`	`}`
`1692`	`1692`	`Debug.assert((getCheckFlags(symbol) & CheckFlags.Instantiated) === 0, "Should never get an instantiated symbol here.");`
`1693`	`1693`	`return (symbol.flags & meaning) \|\| dontResolveAlias ? symbol : resolveAlias(symbol);`
`@@ -16357,7 +16357,7 @@ namespace ts {`
`16357`	`16357`	`// This code-path is called by language service`
`16358`	`16358`	`return resolveStatelessJsxOpeningLikeElement(<JsxOpeningLikeElement>node, checkExpression((<JsxOpeningLikeElement>node).tagName), candidatesOutArray);`
`16359`	`16359`	`}`
`16360`		`- Debug.fail("Branch in 'resolveSignature' should be unreachable.");`
	`16360`	`+ Debug.assertNever(node, "Branch in 'resolveSignature' should be unreachable.");`
`16361`	`16361`	`}`
`16362`	`16362`
`16363`	`16363`	`/**`
`@@ -24535,7 +24535,7 @@ namespace ts {`
`24535`	`24535`	`currentKind = SetAccessor;`
`24536`	`24536`	`}`
`24537`	`24537`	`else {`
`24538`		`- Debug.fail("Unexpected syntax kind:" + (<Node>prop).kind);`
	`24538`	`+ Debug.assertNever(prop, "Unexpected syntax kind:" + (<Node>prop).kind);`
`24539`	`24539`	`}`
`24540`	`24540`
`24541`	`24541`	`const effectiveName = getPropertyNameForPropertyNameNode(name);`