Support Flow this parameter annotations (#12234)

packages/babel-generator/src/generators/flow.ts

@@ -289,6 +289,18 @@ export function FunctionTypeAnnotation(
 ) {
   this.print(node.typeParameters, node);
   this.token("(");
+
+  if (node.this) {
+    this.word("this");
+    this.token(":");
+    this.space();
+    this.print(node.this.typeAnnotation, node);
+    if (node.params.length || node.rest) {
+      this.token(",");
+      this.space();
+    }
+  }
+
   this.printList(node.params, node);
 
   if (node.rest) {

packages/babel-generator/test/fixtures/flow/this-param/input.js

@@ -0,0 +1,45 @@
+function one (this : number) {}
+function two (this : number, a) {}
+function three (this : number, ...a) {}
+function four (this : number, a, b, ...c) {}
+function five<T> (this : T) {}
+
+type six = (this : number) => void
+type seven = (this : number, a : number) => void
+type eight = (this : number, ...a : any) => void
+type nine = <T>(this : T) => void
+
+type ten = {
+    m1(this : string) : void,
+    m2(this : string, a : number) : void,
+    m3(this : string, ...a : any) : void,
+    m4<T>(this : T) : void
+}
+
+declare function eleven (this : number) : void
+declare function twelve (this : string, a : number) : void
+declare function thirteen (this : string, ...a : any) : void
+declare function fourteen<T>(this : T) : void
+
+declare class Fifteen {
+    m1(this : string) : void,
+    m2(this : string, a : number) : void,
+    m3(this : string, ...a : any) : void,
+    m4<T>(this : T) : void
+}
+
+class Sixteen {
+    m1 (this : number) {}
+    m2 (this : number, a) {}
+    m3 (this : number, ...a) {}
+    m4 (this : number, a, b, ...c) {}
+    m5<T> (this : T) {}
+}
+
+let seventeen = {
+    m1 (this : number) {},
+    m2 (this : number, a) {},
+    m3 (this : number, ...a) {},
+    m4 (this : number, a, b, ...c) {},
+    m5<T> (this : T) {}
+}

packages/babel-generator/test/fixtures/flow/this-param/output.js

@@ -0,0 +1,56 @@
+function one(this: number) {}
+
+function two(this: number, a) {}
+
+function three(this: number, ...a) {}
+
+function four(this: number, a, b, ...c) {}
+
+function five<T>(this: T) {}
+
+type six = (this: number) => void;
+type seven = (this: number, a: number) => void;
+type eight = (this: number, ...a: any) => void;
+type nine = <T>(this: T) => void;
+type ten = {
+  m1(this: string): void,
+  m2(this: string, a: number): void,
+  m3(this: string, ...a: any): void,
+  m4<T>(this: T): void,
+};
+declare function eleven(this: number): void;
+declare function twelve(this: string, a: number): void;
+declare function thirteen(this: string, ...a: any): void;
+declare function fourteen<T>(this: T): void;
+declare class Fifteen {
+  m1(this: string): void,
+  m2(this: string, a: number): void,
+  m3(this: string, ...a: any): void,
+  m4<T>(this: T): void,
+}
+
+class Sixteen {
+  m1(this: number) {}
+
+  m2(this: number, a) {}
+
+  m3(this: number, ...a) {}
+
+  m4(this: number, a, b, ...c) {}
+
+  m5<T>(this: T) {}
+
+}
+
+let seventeen = {
+  m1(this: number) {},
+
+  m2(this: number, a) {},
+
+  m3(this: number, ...a) {},
+
+  m4(this: number, a, b, ...c) {},
+
+  m5<T>(this: T) {}
+
+};