Explain boolean exception in getIndexedAccessType

sandersn · sandersn · commit 8087206078f0 · 2017-08-28T11:09:25.000-07:00
Booleans are not treated like other unions in order to skip straight to
error reporting so that the error is reported with 'boolean' instead of
'true'.
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -7693,6 +7693,8 @@ namespace ts {
                 return type;
             }
             // In the following we resolve T[K] to the type of the property in T selected by K.
+            // We treat boolean as different from other unions to improve errors;
+            // skipping straight to getPropertyTypeForIndexType gives errors with 'boolean' instead of 'true'.
             const apparentObjectType = getApparentType(objectType);
             if (indexType.flags & TypeFlags.Union && !(indexType.flags & TypeFlags.Boolean)) {
                 const propTypes: Type[] = [];

Original file line number	Diff line number	Diff line change
`@@ -7693,6 +7693,8 @@ namespace ts {`
`7693`	`7693`	`return type;`
`7694`	`7694`	`}`
`7695`	`7695`	`// In the following we resolve T[K] to the type of the property in T selected by K.`
	`7696`	`+ // We treat boolean as different from other unions to improve errors;`
	`7697`	`+ // skipping straight to getPropertyTypeForIndexType gives errors with 'boolean' instead of 'true'.`
`7696`	`7698`	`const apparentObjectType = getApparentType(objectType);`
`7697`	`7699`	`if (indexType.flags & TypeFlags.Union && !(indexType.flags & TypeFlags.Boolean)) {`
`7698`	`7700`	`const propTypes: Type[] = [];`