Error on circular constraints in mapped types

ahejlsberg · ahejlsberg · commit 63387bb5e00d · 2016-11-18T06:13:04.000-08:00
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -6059,6 +6059,9 @@ namespace ts {
                 type.aliasSymbol = getAliasSymbolForTypeNode(node);
                 type.aliasTypeArguments = getAliasTypeArgumentsForTypeNode(node);
                 links.resolvedType = type;
+                // Eagerly resolve the constraint type which forces an error if the constraint type circularly
+                // references itself through one or more type aliases.
+                getConstraintTypeFromMappedType(type);
             }
             return links.resolvedType;
         }

Original file line number	Diff line number	Diff line change
`@@ -6059,6 +6059,9 @@ namespace ts {`
`6059`	`6059`	`type.aliasSymbol = getAliasSymbolForTypeNode(node);`
`6060`	`6060`	`type.aliasTypeArguments = getAliasTypeArgumentsForTypeNode(node);`
`6061`	`6061`	`links.resolvedType = type;`
	`6062`	`+ // Eagerly resolve the constraint type which forces an error if the constraint type circularly`
	`6063`	`+ // references itself through one or more type aliases.`
	`6064`	`+ getConstraintTypeFromMappedType(type);`
`6062`	`6065`	`}`
`6063`	`6066`	`return links.resolvedType;`
`6064`	`6067`	`}`