Port #6628 into release 1.8

src/compiler/checker.ts

@@ -4285,7 +4285,7 @@ namespace ts {
 
         function hasConstraintReferenceTo(type: Type, target: TypeParameter): boolean {
             let checked: Type[];
-            while (type && type.flags & TypeFlags.TypeParameter && !contains(checked, type)) {
+            while (type && !(type.flags & TypeFlags.ThisType) && type.flags & TypeFlags.TypeParameter && !contains(checked, type)) {
                 if (type === target) {
                     return true;
                 }

tests/baselines/reference/thisTypeAsConstraint.js

@@ -0,0 +1,14 @@
+//// [thisTypeAsConstraint.ts]
+class C {
+  public m<T extends this>() {
+  }
+}
+
+//// [thisTypeAsConstraint.js]
+var C = (function () {
+    function C() {
+    }
+    C.prototype.m = function () {
+    };
+    return C;
+}());

tests/baselines/reference/thisTypeAsConstraint.symbols

@@ -0,0 +1,9 @@
+=== tests/cases/compiler/thisTypeAsConstraint.ts ===
+class C {
+>C : Symbol(C, Decl(thisTypeAsConstraint.ts, 0, 0))
+
+  public m<T extends this>() {
+>m : Symbol(m, Decl(thisTypeAsConstraint.ts, 0, 9))
+>T : Symbol(T, Decl(thisTypeAsConstraint.ts, 1, 11))
+  }
+}

tests/baselines/reference/thisTypeAsConstraint.types

@@ -0,0 +1,9 @@
+=== tests/cases/compiler/thisTypeAsConstraint.ts ===
+class C {
+>C : C
+
+  public m<T extends this>() {
+>m : <T extends this>() => void
+>T : T
+  }
+}

tests/cases/compiler/thisTypeAsConstraint.ts

@@ -0,0 +1,4 @@
+class C {
+  public m<T extends this>() {
+  }
+}