Allow flow declarations to break on StringLiteralTypeAnnotations (#1437)

* Allow flow declarations to break on StringLiteralTypeAnnotations

* canBreak

src/printer.js

@@ -1837,18 +1837,27 @@ function genericPrintNoParens(path, options, print, args) {
         parts.push("declare ");
       }
 
+      const canBreak = (
+        n.right.type === "StringLiteralTypeAnnotation"
+      );
+
+      const printed = printAssignmentRight(
+        n.right,
+        path.call(print, "right"),
+        canBreak,
+        options
+      );
+
       parts.push(
         "type ",
         path.call(print, "id"),
         path.call(print, "typeParameters"),
         " =",
-        hasLeadingOwnLineComment(options.originalText, n.right)
-          ? indent(concat([hardline, path.call(print, "right")]))
-          : concat([" ", path.call(print, "right")]),
+        printed,
         semi
       );
 
-      return concat(parts);
+      return group(concat(parts));
     }
     case "TypeCastExpression":
       return concat([
@@ -3345,6 +3354,18 @@ function printBinaryishExpressions(path, print, options, isNested, isInsideParen
   return parts;
 }
 
+function printAssignmentRight(rightNode, printedRight, canBreak, options) {
+  if (hasLeadingOwnLineComment(options.originalText, rightNode)) {
+    return indent(concat([hardline, printedRight]));
+  }
+
+  if (canBreak) {
+    return indent(concat([line, printedRight]));
+  }
+
+  return concat([" ", printedRight]);
+}
+
 function printAssignment(
   leftNode,
   printedLeft,
@@ -3357,20 +3378,20 @@ function printAssignment(
     return printedLeft;
   }
 
-  let printed;
-  if (hasLeadingOwnLineComment(options.originalText, rightNode)) {
-    printed = indent(concat([hardline, printedRight]));
-  } else if (
+  const canBreak = (
     (isBinaryish(rightNode) && !shouldInlineLogicalExpression(rightNode)) ||
     (leftNode.type === "Identifier" || leftNode.type === "MemberExpression") &&
       (rightNode.type === "StringLiteral" ||
         (rightNode.type === "Literal" && typeof rightNode.value === "string") ||
         isMemberExpressionChain(rightNode))
-  ) {
-    printed = indent(concat([line, printedRight]));
-  } else {
-    printed = concat([" ", printedRight]);
-  }
+  );
+
+  const printed = printAssignmentRight(
+    rightNode,
+    printedRight,
+    canBreak,
+    options
+  );
 
   return group(concat([printedLeft, " ", operator, printed]));
 }

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

@@ -0,0 +1,22 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`long.js 1`] = `
+export type AdamPlacementValidationSingleErrorKey =
+  'SOME_FANCY_TARGETS.GLOBAL_TARGET';
+
+export type SomeReallyLongLongLongLongLongLongLongLongLongLongLongLongLongLongKey = true;
+
+export type SomeOtherLongLongLongLongLongLongLongLongLongLongLongLongLongLongKey = null;
+
+type SomeOtherLongLongLongLongLongLongLongLongLongLongLongLongLongLongKey = SomeReallyLongLongLongLongLongLongIdentifier;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+export type AdamPlacementValidationSingleErrorKey =
+  "SOME_FANCY_TARGETS.GLOBAL_TARGET";
+
+export type SomeReallyLongLongLongLongLongLongLongLongLongLongLongLongLongLongKey = true;
+
+export type SomeOtherLongLongLongLongLongLongLongLongLongLongLongLongLongLongKey = null;
+
+type SomeOtherLongLongLongLongLongLongLongLongLongLongLongLongLongLongKey = SomeReallyLongLongLongLongLongLongIdentifier;
+
+`;

tests/flow_type_declarations/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname, null, ["babylon"]);

tests/flow_type_declarations/long.js

@@ -0,0 +1,8 @@
+export type AdamPlacementValidationSingleErrorKey =
+  'SOME_FANCY_TARGETS.GLOBAL_TARGET';
+
+export type SomeReallyLongLongLongLongLongLongLongLongLongLongLongLongLongLongKey = true;
+
+export type SomeOtherLongLongLongLongLongLongLongLongLongLongLongLongLongLongKey = null;
+
+type SomeOtherLongLongLongLongLongLongLongLongLongLongLongLongLongLongKey = SomeReallyLongLongLongLongLongLongIdentifier;