Remove redundant backticks: do not report if variable inside the string and isn't followed by space

#KT-35051 Fixed

idea/src/org/jetbrains/kotlin/idea/inspections/RemoveRedundantBackticksInspection.kt

@@ -19,6 +19,7 @@ import com.intellij.codeInspection.LocalQuickFix
 import com.intellij.codeInspection.ProblemDescriptor
 import com.intellij.codeInspection.ProblemHighlightType
 import com.intellij.codeInspection.ProblemsHolder
+import com.intellij.lang.ASTNode
 import com.intellij.openapi.project.Project
 import com.intellij.psi.PsiElement
 import com.intellij.psi.PsiElementVisitor
@@ -26,9 +27,9 @@ import com.intellij.psi.impl.source.tree.SharedImplUtil
 import org.jetbrains.kotlin.idea.KotlinBundle
 import org.jetbrains.kotlin.idea.core.unquote
 import org.jetbrains.kotlin.lexer.KtTokens
-import org.jetbrains.kotlin.psi.KtElement
-import org.jetbrains.kotlin.psi.KtPsiFactory
-import org.jetbrains.kotlin.psi.KtVisitorVoid
+import org.jetbrains.kotlin.psi.*
+import org.jetbrains.kotlin.psi.psiUtil.canPlaceAfterSimpleNameEntry
+import org.jetbrains.kotlin.psi.psiUtil.getStrictParentOfType
 import org.jetbrains.kotlin.psi.psiUtil.isIdentifier
 
 class RemoveRedundantBackticksInspection : AbstractKotlinInspection() {
@@ -37,7 +38,7 @@ class RemoveRedundantBackticksInspection : AbstractKotlinInspection() {
             override fun visitKtElement(element: KtElement) {
                 super.visitKtElement(element)
                 SharedImplUtil.getChildrenOfType(element.node, KtTokens.IDENTIFIER).forEach {
-                    if (isRedundantBackticks(it.text)) {
+                    if (isRedundantBackticks(it)) {
                         registerProblem(holder, it.psi)
                     }
                 }
@@ -61,7 +62,7 @@ class RemoveRedundantBackticksQuickFix : LocalQuickFix {
 
     override fun applyFix(project: Project, descriptor: ProblemDescriptor) {
         val element = descriptor.psiElement
-        if (!isRedundantBackticks(element.text)) return
+        if (!isRedundantBackticks(element.node)) return
         val factory = KtPsiFactory(project)
         element.replace(factory.createIdentifier(element.text.unquote()))
     }
@@ -70,8 +71,11 @@ class RemoveRedundantBackticksQuickFix : LocalQuickFix {
 private fun isKeyword(text: String): Boolean =
     text == "yield" || text.all { it == '_' } || (KtTokens.KEYWORDS.types + KtTokens.SOFT_KEYWORDS.types).any { it.toString() == text }
 
-private fun isRedundantBackticks(identifier: String): Boolean {
+private fun isRedundantBackticks(node: ASTNode): Boolean {
+    val identifier = node.text
     if (!(identifier.startsWith("`") && identifier.endsWith("`"))) return false
     val unquotedText = identifier.unquote()
-    return unquotedText.isIdentifier() && !isKeyword(unquotedText)
+    if (!unquotedText.isIdentifier() || isKeyword(unquotedText)) return false
+    val simpleNameStringTemplateEntry = node.psi.getStrictParentOfType<KtSimpleNameStringTemplateEntry>()
+    return simpleNameStringTemplateEntry == null || canPlaceAfterSimpleNameEntry(simpleNameStringTemplateEntry.nextSibling)
 }

idea/testData/inspectionsLocal/removeRedundantBackticks/inStringTemplate.kt

@@ -0,0 +1,5 @@
+// PROBLEM: none
+fun main() {
+    val name = "Kotlin"
+    val test = "$<caret>`name`test"
+}

idea/testData/inspectionsLocal/removeRedundantBackticks/inStringTemplate2.kt

@@ -0,0 +1,4 @@
+fun main() {
+    val name = "Kotlin"
+    val test = "$<caret>`name` test"
+}

idea/testData/inspectionsLocal/removeRedundantBackticks/inStringTemplate2.kt.after

@@ -0,0 +1,4 @@
+fun main() {
+    val name = "Kotlin"
+    val test = "$name test"
+}

idea/testData/inspectionsLocal/removeRedundantBackticks/inStringTemplate3.kt

@@ -0,0 +1,4 @@
+fun main() {
+    val name = "Kotlin"
+    val test = "${<caret>`name`}test"
+}

idea/testData/inspectionsLocal/removeRedundantBackticks/inStringTemplate3.kt.after

@@ -0,0 +1,4 @@
+fun main() {
+    val name = "Kotlin"
+    val test = "${name}test"
+}

idea/tests/org/jetbrains/kotlin/idea/inspections/LocalInspectionTestGenerated.java

@@ -9545,6 +9545,21 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
             runTest("idea/testData/inspectionsLocal/removeRedundantBackticks/identifierContainingSpaces.kt");
         }
 
+        @TestMetadata("inStringTemplate.kt")
+        public void testInStringTemplate() throws Exception {
+            runTest("idea/testData/inspectionsLocal/removeRedundantBackticks/inStringTemplate.kt");
+        }
+
+        @TestMetadata("inStringTemplate2.kt")
+        public void testInStringTemplate2() throws Exception {
+            runTest("idea/testData/inspectionsLocal/removeRedundantBackticks/inStringTemplate2.kt");
+        }
+
+        @TestMetadata("inStringTemplate3.kt")
+        public void testInStringTemplate3() throws Exception {
+            runTest("idea/testData/inspectionsLocal/removeRedundantBackticks/inStringTemplate3.kt");
+        }
+
         @TestMetadata("keyword.kt")
         public void testKeyword() throws Exception {
             runTest("idea/testData/inspectionsLocal/removeRedundantBackticks/keyword.kt");