Bug 1901457 part 4: Implement ITextProvider::get_SupportedTextSelection. r=nlapre

Differential Revision: https://phabricator.services.mozilla.com/D214344

accessible/tests/browser/windows/uia/browser_textPatterns.js

@@ -4,6 +4,11 @@
 
 "use strict";
 
+/* eslint-disable camelcase */
+const SupportedTextSelection_None = 0;
+const SupportedTextSelection_Multiple = 2;
+/* eslint-enable camelcase */
+
 /**
  * Test the Text pattern's DocumentRange property. This also tests where the
  * Text pattern is exposed.
@@ -662,3 +667,40 @@ addUiaTask(
     is(await runPython(`range.GetText(-1)`), "i", "range text correct");
   }
 );
+
+/**
+ * Test the Text pattern's SupportedTextSelection property.
+ */
+addUiaTask(
+  `
+<style>
+body {
+  user-select: none;
+}
+</style>
+<input id="input">
+  `,
+  async function testTextSupportedTextSelection() {
+    let result = await runPython(`
+      global doc
+      doc = getDocUia()
+      input = findUiaByDomId(doc, "input")
+      text = getUiaPattern(input, "Text")
+      return text.SupportedTextSelection
+    `);
+    is(
+      result,
+      SupportedTextSelection_Multiple,
+      "input SupportedTextSelection correct"
+    );
+    // The IA2 -> UIA bridge doesn't understand that text isn't selectable in
+    // this document.
+    if (gIsUiaEnabled) {
+      is(
+        await runPython(`getUiaPattern(doc, "Text").SupportedTextSelection`),
+        SupportedTextSelection_None,
+        "doc SupportedTextSelection correct"
+      );
+    }
+  }
+);

accessible/windows/uia/UiaText.cpp

@@ -7,6 +7,7 @@
 #include "UiaText.h"
 
 #include "ia2AccessibleHypertext.h"
+#include "mozilla/a11y/States.h"
 #include "TextLeafRange.h"
 #include "UiaTextRange.h"
 
@@ -67,5 +68,17 @@ UiaText::get_DocumentRange(__RPC__deref_out_opt ITextRangeProvider** aRetVal) {
 STDMETHODIMP
 UiaText::get_SupportedTextSelection(
     __RPC__out enum SupportedTextSelection* aRetVal) {
-  return E_NOTIMPL;
+  if (!aRetVal) {
+    return E_INVALIDARG;
+  }
+  Accessible* acc = Acc();
+  if (!acc) {
+    return CO_E_OBJNOTCONNECTED;
+  }
+  if (acc->State() & states::SELECTABLE_TEXT) {
+    *aRetVal = SupportedTextSelection_Multiple;
+  } else {
+    *aRetVal = SupportedTextSelection_None;
+  }
+  return S_OK;
 }