[inline-completion] IDEA-373460: fix 'insert inline completion' at the start of RTL text

(cherry picked from commit 4dcdf0e831082252f1e4deb123cd9d9efd4fb3e9)

IJ-MR-164742

GitOrigin-RevId: 6f4c509174230355054656ff905a68ae4a8eb82e

platform/platform-impl/codeinsight-inline/src/com/intellij/codeInsight/inline/completion/render/InlineCompletionTextRenderManager.kt

@@ -306,6 +306,10 @@ internal class InlineCompletionTextRenderManager private constructor(
     }
 
     private fun Editor.forceLeanLeft() {
+      if (caretModel.currentCaret.isAtRtlLocation) {
+        // IDEA-373460: otherwise, we may move the caret which invalidates the current inline completion session
+        return
+      }
       val visualPosition = caretModel.visualPosition
       if (visualPosition.leansRight) {
         val leftLeaningPosition = VisualPosition(visualPosition.line, visualPosition.column, false)

platform/platform-tests/testSrc/com/intellij/codeInsight/inline/completion/RTLInlineCompletionTest.kt

@@ -0,0 +1,57 @@
+// Copyright 2000-2025 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+package com.intellij.codeInsight.inline.completion
+
+import com.intellij.codeInsight.inline.completion.elements.InlineCompletionElement
+import com.intellij.codeInsight.inline.completion.elements.InlineCompletionGrayTextElement
+import com.intellij.codeInsight.inline.completion.impl.SimpleInlineCompletionProvider
+import com.intellij.openapi.fileTypes.PlainTextFileType
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+
+@RunWith(JUnit4::class)
+internal class RTLInlineCompletionTest : InlineCompletionTestCase() {
+
+  private fun registerSuggestion(vararg suggestion: InlineCompletionElement) {
+    InlineCompletionHandler.registerTestHandler(Provider(suggestion.toList()), testRootDisposable)
+  }
+
+  @Test
+  fun `test accept RTL inline suggestion at the start position`() = myFixture.testInlineCompletion {
+    init(PlainTextFileType.INSTANCE, "<caret> مرحبا، كيف حالك")
+    caret {
+      // Forcing RTL
+      moveRight(); moveRight()
+    }
+    registerSuggestion(InlineCompletionGrayTextElement("اليوم؟"))
+    callInlineCompletion()
+    delay()
+    assertInlineRender("اليوم؟")
+    typeChar('ا')
+    assertInlineRender("ليوم؟")
+    insertWithTab()
+    assertInlineHidden()
+    assertFileContent(" مرحبا، كيف حالكاليوم؟<caret>") // it's actually " <caret>arabic". It's just rendered this way in IJ.
+  }
+
+  @Test
+  fun `test accept RTL inline suggestion inside RTL part`() = myFixture.testInlineCompletion {
+    init(PlainTextFileType.INSTANCE, "<caret> مرحبا، كيف حالك")
+    caret {
+      // RTL position after the first (last) letter
+      moveRight(); moveRight(); moveRight()
+    }
+    registerSuggestion(InlineCompletionGrayTextElement("اليوم؟"))
+    callInlineCompletion()
+    delay()
+    assertInlineRender("اليوم؟")
+    insertWithTab()
+    assertFileContent(" مرحبا، كيف حالاليوم؟<caret>ك")
+  }
+
+  private class Provider(suggestion: List<InlineCompletionElement>) : SimpleInlineCompletionProvider(suggestion) {
+    override fun isEnabled(event: InlineCompletionEvent): Boolean {
+      return super.isEnabled(event) || event is InlineCompletionEvent.DirectCall
+    }
+  }
+}

platform/platform-tests/testSrc/com/intellij/codeInsight/inline/completion/impl/InlineCompletionProviders.kt

@@ -81,7 +81,7 @@ internal class GradualMultiSuggestInlineCompletionProvider(
   }
 }
 
-internal class SimpleInlineCompletionProvider(val suggestion: List<InlineCompletionElement>) : InlineCompletionProvider {
+internal open class SimpleInlineCompletionProvider(val suggestion: List<InlineCompletionElement>) : InlineCompletionProvider {
   override val id: InlineCompletionProviderID = InlineCompletionProviderID("SimpleInlineCompletionProvider")
 
   override suspend fun getSuggestion(request: InlineCompletionRequest): InlineCompletionSingleSuggestion {