Rename SafeValue to ToStringValue (facebook#13376)

Following up on the changes I made in facebook#13367, @gaearon suggest that
"safe" could be read as necessary for security. To avoid misleading a
reader, I'm changing the name.

A few names where discussed in the previous PR. I think `ToStringValue`
makes sense since the value itself is not a string yet but an opaque
type that can be cast to a string. For the actual string concatenation,
I've used `toString` now to avoid confusion: `toStringValueToString`
is super weird and it's namespaced anyhow.

Definitely open for suggestions here. :) I'll wait until we wrap up
facebook#13362 and take care of rebase afterwards.

packages/react-dom/src/client/ReactDOMFiberInput.js

@@ -14,15 +14,15 @@ import warning from 'shared/warning';
 
 import * as DOMPropertyOperations from './DOMPropertyOperations';
 import {getFiberCurrentPropsFromNode} from './ReactDOMComponentTree';
-import {getSafeValue, safeValueToString} from './SafeValue';
+import {getToStringValue, toString} from './ToStringValue';
 import ReactControlledValuePropTypes from '../shared/ReactControlledValuePropTypes';
 import * as inputValueTracking from './inputValueTracking';
 
-import type {SafeValue} from './SafeValue';
+import type {ToStringValue} from './ToStringValue';
 
 type InputWithWrapperState = HTMLInputElement & {
   _wrapperState: {
-    initialValue: SafeValue,
+    initialValue: ToStringValue,
     initialChecked: ?boolean,
     controlled?: boolean,
   },
@@ -117,7 +117,7 @@ export function initWrapperState(element: Element, props: Object) {
   node._wrapperState = {
     initialChecked:
       props.checked != null ? props.checked : props.defaultChecked,
-    initialValue: getSafeValue(
+    initialValue: getToStringValue(
       props.value != null ? props.value : defaultValue,
     ),
     controlled: isControlled(props),
@@ -171,7 +171,7 @@ export function updateWrapper(element: Element, props: Object) {
 
   updateChecked(element, props);
 
-  const value = getSafeValue(props.value);
+  const value = getToStringValue(props.value);
 
   if (value != null) {
     if (props.type === 'number') {
@@ -181,17 +181,17 @@ export function updateWrapper(element: Element, props: Object) {
         // eslint-disable-next-line
         node.value != (value: any)
       ) {
-        node.value = safeValueToString(value);
+        node.value = toString(value);
       }
-    } else if (node.value !== safeValueToString(value)) {
-      node.value = safeValueToString(value);
+    } else if (node.value !== toString(value)) {
+      node.value = toString(value);
     }
   }
 
   if (props.hasOwnProperty('value')) {
     setDefaultValue(node, props.type, value);
   } else if (props.hasOwnProperty('defaultValue')) {
-    setDefaultValue(node, props.type, getSafeValue(props.defaultValue));
+    setDefaultValue(node, props.type, getToStringValue(props.defaultValue));
   }
 
   if (props.checked == null && props.defaultChecked != null) {
@@ -207,7 +207,7 @@ export function postMountWrapper(
   const node = ((element: any): InputWithWrapperState);
 
   if (props.hasOwnProperty('value') || props.hasOwnProperty('defaultValue')) {
-    const initialValue = safeValueToString(node._wrapperState.initialValue);
+    const initialValue = toString(node._wrapperState.initialValue);
     const currentValue = node.value;
 
     // Do not assign value if it is already set. This prevents user text input
@@ -316,9 +316,9 @@ export function setDefaultValue(
     node.ownerDocument.activeElement !== node
   ) {
     if (value == null) {
-      node.defaultValue = safeValueToString(node._wrapperState.initialValue);
-    } else if (node.defaultValue !== safeValueToString(value)) {
-      node.defaultValue = safeValueToString(value);
+      node.defaultValue = toString(node._wrapperState.initialValue);
+    } else if (node.defaultValue !== toString(value)) {
+      node.defaultValue = toString(value);
     }
   }
 }

packages/react-dom/src/client/SafeValue.js → packages/react-dom/src/client/ToStringValue.js

@@ -7,16 +7,22 @@
  * @flow
  */
 
-export opaque type SafeValue = boolean | number | Object | string | null | void;
+export opaque type ToStringValue =
+  | boolean
+  | number
+  | Object
+  | string
+  | null
+  | void;
 
 // Flow does not allow string concatenation of most non-string types. To work
 // around this limitation, we use an opaque type that can only be obtained by
-// passing the value through getSafeValue first.
-export function safeValueToString(value: SafeValue): string {
+// passing the value through getToStringValue first.
+export function toString(value: ToStringValue): string {
   return '' + (value: any);
 }
 
-export function getSafeValue(value: mixed): SafeValue {
+export function getToStringValue(value: mixed): ToStringValue {
   switch (typeof value) {
     case 'boolean':
     case 'number':