Inline Generics with a single identifier (#5066)

src/language-js/printer-estree.js

@@ -3429,6 +3429,28 @@ function shouldGroupFirstArg(args) {
   );
 }
 
+function isSimpleFlowType(node) {
+  const flowTypeAnnotations = [
+    "AnyTypeAnnotation",
+    "NullLiteralTypeAnnotation",
+    "GenericTypeAnnotation",
+    "ThisTypeAnnotation",
+    "NumberTypeAnnotation",
+    "VoidTypeAnnotation",
+    "EmptyTypeAnnotation",
+    "MixedTypeAnnotation",
+    "BooleanTypeAnnotation",
+    "BooleanLiteralTypeAnnotation",
+    "StringTypeAnnotation"
+  ];
+
+  return (
+    node &&
+    flowTypeAnnotations.indexOf(node.type) !== -1 &&
+    !(node.type === "GenericTypeAnnotation" && node.typeParameters)
+  );
+}
+
 const functionCompositionFunctionNames = new Set([
   "pipe", // RxJS, Ramda
   "pipeP", // Ramda
@@ -3718,20 +3740,6 @@ function printFunctionParams(path, print, options, expandArg, printTypeParams) {
     return concat([typeParams, "(", join(", ", printed), ")"]);
   }
 
-  const flowTypeAnnotations = [
-    "AnyTypeAnnotation",
-    "NullLiteralTypeAnnotation",
-    "GenericTypeAnnotation",
-    "ThisTypeAnnotation",
-    "NumberTypeAnnotation",
-    "VoidTypeAnnotation",
-    "EmptyTypeAnnotation",
-    "MixedTypeAnnotation",
-    "BooleanTypeAnnotation",
-    "BooleanLiteralTypeAnnotation",
-    "StringTypeAnnotation"
-  ];
-
   const isFlowShorthandWithOneArg =
     (isObjectTypePropertyAFunction(parent, options) ||
       isTypeAnnotationAFunction(parent, options) ||
@@ -3745,12 +3753,7 @@ function printFunctionParams(path, print, options, expandArg, printTypeParams) {
     fun[paramsField][0].name === null &&
     fun[paramsField][0].typeAnnotation &&
     fun.typeParameters === null &&
-    flowTypeAnnotations.indexOf(fun[paramsField][0].typeAnnotation.type) !==
-      -1 &&
-    !(
-      fun[paramsField][0].typeAnnotation.type === "GenericTypeAnnotation" &&
-      fun[paramsField][0].typeAnnotation.typeParameters
-    ) &&
+    isSimpleFlowType(fun[paramsField][0].typeAnnotation) &&
     !fun.rest;
 
   if (isFlowShorthandWithOneArg) {
@@ -5648,7 +5651,7 @@ function isNodeStartingWithDeclare(node, options) {
 }
 
 function shouldHugType(node) {
-  if (isObjectType(node)) {
+  if (isSimpleFlowType(node) || isObjectType(node)) {
     return true;
   }
 

tests/flow_generic/__snapshots__/jsfmt.spec.js.snap

@@ -136,6 +136,20 @@ function foo(): Promise<?boolean> {}
 
 `;
 
+exports[`single-identifier.js - flow-verify 1`] = `
+const longVariableName: Array<number> = this.foo.bar.baz.collider.body.vertices.reduce();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+const longVariableName: Array<number> = this.foo.bar.baz.collider.body.vertices.reduce();
+
+`;
+
+exports[`single-identifier.js - flow-verify 2`] = `
+const longVariableName: Array<number> = this.foo.bar.baz.collider.body.vertices.reduce();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+const longVariableName: Array<number> = this.foo.bar.baz.collider.body.vertices.reduce();
+
+`;
+
 exports[`trailing.js - flow-verify 1`] = `
 type State = {
   errors: Immutable.Map<

tests/flow_generic/single-identifier.js

@@ -0,0 +1 @@
+const longVariableName: Array<number> = this.foo.bar.baz.collider.body.vertices.reduce();