Bug 1635675 - Implement the ::file-chooser-button pseudo-element. r=jwatt

As per https://github.com/w3c/csswg-drafts/issues/5049.

Don't enable it unconditionally just yet, as the name may change.

I had to move some rules in forms.css because otherwise you get
specificity conflicts.

Differential Revision: https://phabricator.services.mozilla.com/D76214

devtools/server/actors/styles.js

@@ -748,6 +748,8 @@ var PageStyleActor = protocol.ActorClassWithSpec(pageStyleSpec, {
         return true;
       case ":cue":
         return node.nodeName == "VIDEO";
+      case ":file-chooser-button":
+        return node.nodeName == "INPUT" && node.type == "file";
       case ":placeholder":
       case ":-moz-placeholder":
         return this._nodeIsTextfieldLike(node);

devtools/shared/css/generated/properties-db.js

@@ -10692,7 +10692,8 @@ exports.PSEUDO_ELEMENTS = [
   ":-moz-range-thumb",
   ":-moz-meter-bar",
   ":placeholder",
-  ":-moz-color-swatch"
+  ":-moz-color-swatch",
+  ":file-chooser-button"
 ];
 
 /**

layout/forms/nsFileControlFrame.cpp

@@ -212,6 +212,7 @@ static already_AddRefed<Element> MakeAnonButton(Document* aDoc,
   // NOTE: SetIsNativeAnonymousRoot() has to be called before setting any
   // attribute.
   button->SetIsNativeAnonymousRoot();
+  button->SetPseudoElementType(PseudoStyleType::fileChooserButton);
 
   // Set the file picking button text depending on the current locale.
   nsAutoString buttonTxt;

layout/inspector/tests/test_getCSSPseudoElementNames.html

@@ -15,6 +15,7 @@
     ":marker",
     ":backdrop",
     ":cue",
+    ":file-chooser-button",
     ":first-letter",
     ":first-line",
     ":placeholder",

layout/style/nsCSSPseudoElementList.h

@@ -97,3 +97,7 @@ CSS_PSEUDO_ELEMENT(mozTextControlEditingRoot, ":-moz-text-control-editing-root",
 // The element that shows the autofill value.
 CSS_PSEUDO_ELEMENT(mozTextControlPreview, ":-moz-text-control-preview",
                    CSS_PSEUDO_ELEMENT_ENABLED_IN_UA_SHEETS)
+
+CSS_PSEUDO_ELEMENT(fileChooserButton, ":file-chooser-button",
+                   CSS_PSEUDO_ELEMENT_ENABLED_IN_UA_SHEETS |
+                   CSS_PSEUDO_ELEMENT_SUPPORTS_USER_ACTION_STATE)

layout/style/nsCSSPseudoElements.h

@@ -118,12 +118,20 @@ class nsCSSPseudoElements {
                                  CSS_PSEUDO_ELEMENT_IS_FLEX_OR_GRID_ITEM);
   }
 
-  static bool IsEnabled(Type aType, EnabledState aEnabledState) {
-    if (!PseudoElementHasAnyFlag(
-            aType, CSS_PSEUDO_ELEMENT_ENABLED_IN_UA_SHEETS_AND_CHROME)) {
-      if (aType == Type::mozFocusOuter) {
+  static bool EnabledInContent(Type aType) {
+    switch (aType) {
+      case Type::mozFocusOuter:
         return mozilla::StaticPrefs::layout_css_moz_focus_outer_enabled();
-      }
+      case Type::fileChooserButton:
+        return mozilla::StaticPrefs::layout_css_file_chooser_button_enabled();
+      default:
+        return !PseudoElementHasAnyFlag(
+            aType, CSS_PSEUDO_ELEMENT_ENABLED_IN_UA_SHEETS_AND_CHROME);
+    }
+  }
+
+  static bool IsEnabled(Type aType, EnabledState aEnabledState) {
+    if (EnabledInContent(aType)) {
       return true;
     }
 

layout/style/res/forms.css

@@ -124,7 +124,7 @@ textarea {
 }
 
 /* A few properties that we don't want to inherit by default: */
-input, textarea, select, button {
+input, textarea, select, button, ::file-chooser-button {
   text-align: initial;
   text-indent: initial;
   text-shadow: initial;
@@ -461,44 +461,6 @@ input[type="image"]:disabled {
   cursor: unset;
 }
 
-
-/* file selector */
-input[type="file"] {
-  white-space: nowrap !important;
-  overflow: hidden !important;
-  overflow-clip-box: padding-box;
-  color: unset;
-
-  /* Revert rules which apply on all inputs. */
-  -moz-appearance: none;
-  cursor: default;
-
-  border: none;
-  background-color: transparent;
-  padding: unset;
-}
-
-input[type="file"] > label {
-  display: inline-block;
-  min-inline-size: 12em;
-  padding-inline-start: 5px;
-  text-align: match-parent;
-
-  color: unset;
-  font-size: unset;
-  letter-spacing: unset;
-
-  user-select: none;
-  unicode-bidi: plaintext;
-}
-
-/* button part of file selector */
-input[type="file"] > button {
-  font-size: unset;
-  letter-spacing: unset;
-  cursor: unset;
-}
-
 /* colored part of the color selector button */
 ::-moz-color-swatch {
   width: 100%;
@@ -564,6 +526,7 @@ input[type="search"] {
 /* Non text-related properties for buttons: these ones are shared with
    input[type="color"] */
 button,
+::file-chooser-button,
 input:is([type="color"], [type="reset"], [type="button"], [type="submit"]) {
   -moz-appearance: button;
   /* The sum of border and padding on block-start and block-end
@@ -581,6 +544,7 @@ input:is([type="color"], [type="reset"], [type="button"], [type="submit"]) {
 /* Text-related properties for buttons: these ones are not shared with
    input[type="color"] */
 button,
+::file-chooser-button,
 input:is([type="reset"], [type="button"], [type="submit"]) {
   color: ButtonText;
   font: -moz-button;
@@ -594,7 +558,8 @@ input[type="color"] {
   block-size: 23px;
 }
 
-button {
+button,
+::file-chooser-button {
   /* Buttons should lay out like "normal" html, mostly */
   white-space: unset;
   text-indent: 0;
@@ -636,16 +601,19 @@ button {
   justify-items: inherit;
 }
 
+::file-chooser-button:hover,
 button:hover,
 input:is([type="reset"], [type="button"], [type="submit"], [type="color"]):hover {
   background-color: -moz-buttonhoverface;
 }
 
+::file-chooser-button:hover,
 button:hover,
 input:is([type="reset"], [type="button"], [type="submit"]):hover {
   color: -moz-buttonhovertext;
 }
 
+::file-chooser-button:active:hover,
 button:active:hover,
 input:is([type="reset"], [type="button"], [type="submit"], [type="color"]):active:hover {
 %ifndef XP_MACOSX
@@ -656,6 +624,7 @@ input:is([type="reset"], [type="button"], [type="submit"], [type="color"]):activ
   background-color: ButtonFace;
 }
 
+::file-chooser-button:active:hover,
 button:active:hover,
 input:is([type="reset"], [type="button"], [type="submit"]):active:hover {
 %ifdef MOZ_WIDGET_GTK
@@ -676,6 +645,7 @@ input:is([type="reset"], [type="button"], [type="submit"]):active:hover {
   border-color: currentColor;
 }
 
+:is(:disabled, :disabled:active)::file-chooser-button,
 button:is(:disabled, :disabled:active),
 input:is([type="reset"], [type="button"], [type="submit"], [type="color"]):is(:disabled, :disabled:active),
 select:is(:disabled, :disabled:active) > button {
@@ -687,12 +657,50 @@ select:is(:disabled, :disabled:active) > button {
   cursor: unset;
 }
 
+:is(:disabled, :disabled:active)::file-chooser-button,
 button:is(:disabled, :disabled:active),
 input:is([type="reset"], [type="button"], [type="submit"]):is(:disabled, :disabled:active),
 select:is(:disabled, :disabled:active) > button {
   color: GrayText;
 }
 
+/* file selector */
+input[type="file"] {
+  white-space: nowrap !important;
+  overflow: hidden !important;
+  overflow-clip-box: padding-box;
+  color: unset;
+
+  /* Revert rules which apply on all inputs. */
+  -moz-appearance: none;
+  cursor: default;
+
+  border: none;
+  background-color: transparent;
+  padding: unset;
+}
+
+input[type="file"] > label {
+  display: inline-block;
+  min-inline-size: 12em;
+  padding-inline-start: 5px;
+  text-align: match-parent;
+
+  color: unset;
+  font-size: unset;
+  letter-spacing: unset;
+
+  user-select: none;
+  unicode-bidi: plaintext;
+}
+
+/* button part of file selector */
+::file-chooser-button {
+  font-size: unset;
+  letter-spacing: unset;
+  cursor: unset;
+}
+
  /*
   * Make form controls inherit 'unicode-bidi' transparently as required by
   *  their various anonymous descendants and pseudo-elements:

modules/libpref/init/StaticPrefList.yaml

@@ -6218,6 +6218,13 @@
   mirror: always
   rust: true
 
+# Is support for the ::file-chooser-button pseudo-element enabled?
+- name: layout.css.file-chooser-button.enabled
+  type: RelaxedAtomicBool
+  value: @IS_NIGHTLY_OR_DEV_EDITION@
+  mirror: always
+  rust: true
+
 # Whether the computed value of line-height: normal returns the `normal`
 # keyword rather than a pixel value based on the first available font.
 #

servo/components/style/gecko/pseudo_element.rs

@@ -37,7 +37,8 @@ impl ::selectors::parser::PseudoElement for PseudoElement {
             PseudoElement::Before |
                 PseudoElement::After |
                 PseudoElement::Marker |
-                PseudoElement::Placeholder
+                PseudoElement::Placeholder |
+                PseudoElement::FileChooserButton
         )
     }
 
@@ -159,12 +160,12 @@ impl PseudoElement {
 
     /// Whether this pseudo-element is enabled for all content.
     pub fn enabled_in_content(&self) -> bool {
-        if (self.flags() & structs::CSS_PSEUDO_ELEMENT_ENABLED_IN_UA_SHEETS_AND_CHROME) != 0 {
-            return false;
-        }
         match *self {
             PseudoElement::MozFocusOuter => static_prefs::pref!("layout.css.moz-focus-outer.enabled"),
-            _ => true,
+            PseudoElement::FileChooserButton => static_prefs::pref!("layout.css.file-chooser-button.enabled"),
+            _ => {
+                (self.flags() & structs::CSS_PSEUDO_ELEMENT_ENABLED_IN_UA_SHEETS_AND_CHROME) == 0
+            }
         }
     }
 

testing/web-platform/tests/css/css-pseudo/file-chooser-button-001-notref.html

@@ -0,0 +1,3 @@
+<!doctype html>
+<title>CSS Test Reference</title>
+<input type="file">

testing/web-platform/tests/css/css-pseudo/file-chooser-button-001.tentative.html

@@ -0,0 +1,10 @@
+<!doctype html>
+<title>::file-chooser-button allows to customize the button in &lt;input type=file&gt;</title>
+<link rel="mismatch" href="file-chooser-button-001-notref.html">
+<style>
+  input::file-chooser-button {
+    background: green;
+    color: white;
+  }
+</style>
+<input type="file">

xpcom/ds/StaticAtoms.py

@@ -2489,6 +2489,7 @@ STATIC_ATOMS = [
     PseudoElementAtom("PseudoElement_mozColorSwatch", ":-moz-color-swatch"),
     PseudoElementAtom("PseudoElement_mozTextControlEditingRoot", ":-moz-text-control-editing-root"),
     PseudoElementAtom("PseudoElement_mozTextControlPreview", ":-moz-text-control-preview"),
+    PseudoElementAtom("PseudoElement_fileChooserButton", ":file-chooser-button"),
 
     # CSS anonymous boxes -- these must appear in the same order as
     # in nsCSSAnonBoxList.h