Fix IR generation for string templates containing single entry.

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/StatementGenerator.kt

@@ -203,18 +203,20 @@ class StatementGenerator(
 
     override fun visitStringTemplateExpression(expression: KtStringTemplateExpression, data: Nothing?): IrStatement {
         val entries = expression.entries
-        when (entries.size) {
+        val resultType = getInferredTypeWithImplicitCastsOrFail(expression)
-            1 -> return entries[0].genExpr()
+        return when (entries.size) {
-            0 -> return IrConstImpl.string(expression.startOffset, expression.endOffset,
+            1 -> {
-                                           getInferredTypeWithImplicitCastsOrFail(expression), "")
+                val irArg = entries[0].genExpr()
+                if (irArg is IrConst<*> && irArg.kind == IrConstKind.String)
+                    irArg
+                else
+                    IrStringConcatenationImpl(expression.startOffset, expression.endOffset, resultType, listOf(irArg))
+            }
+            0 ->
+                IrConstImpl.string(expression.startOffset, expression.endOffset, resultType, "")
+            else ->
+                IrStringConcatenationImpl(expression.startOffset, expression.endOffset, resultType, entries.map { it.genExpr() })
         }
-
-        val irStringTemplate = IrStringConcatenationImpl(expression.startOffset, expression.endOffset,
-                                                                                             getInferredTypeWithImplicitCastsOrFail(expression))
-        entries.forEach {
-            irStringTemplate.addArgument(it.genExpr())
-        }
-        return irStringTemplate
     }
 
     override fun visitLiteralStringTemplateEntry(entry: KtLiteralStringTemplateEntry, data: Nothing?): IrStatement =
@@ -267,7 +269,7 @@ class StatementGenerator(
                             IrGetEnumValueImpl(expression.startOffset, expression.endOffset, classValueType, descriptor)
                         else -> {
                             IrGetObjectValueImpl(expression.startOffset, expression.endOffset, classValueType,
-                                                                                     descriptor.companionObjectDescriptor ?: throw AssertionError("Class value without companion object: $descriptor"))
+                                                 descriptor.companionObjectDescriptor ?: throw AssertionError("Class value without companion object: $descriptor"))
                         }
                     }
                 }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrStringConcatenationImpl.kt

@@ -16,20 +16,19 @@
 
 package org.jetbrains.kotlin.ir.expressions.impl
 
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrStringConcatenation
-import org.jetbrains.kotlin.ir.expressions.impl.IrExpressionBase
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 import java.util.*
 
-class IrStringConcatenationImpl(
+class IrStringConcatenationImpl(startOffset: Int, endOffset: Int, type: KotlinType) :
-        startOffset: Int,
+        IrExpressionBase(startOffset, endOffset, type), IrStringConcatenation {
-        endOffset: Int,
+    constructor(startOffset: Int, endOffset: Int, type: KotlinType, arguments: Collection<IrExpression>) : this(startOffset, endOffset, type) {
-        type: KotlinType
+        this.arguments.addAll(arguments)
-) : IrExpressionBase(startOffset, endOffset, type), IrStringConcatenation {
+    }
+
     override val arguments: MutableList<IrExpression> = ArrayList()
 
     override fun addArgument(argument: IrExpression) {

compiler/testData/ir/irText/expressions/stringTemplates.kt

@@ -1,4 +1,5 @@
 fun foo(): String = ""
+val x = 42
 
 val test1 = ""
 val test2 = "abc"
@@ -7,4 +8,8 @@ val test4 = """abc"""
 val test5 = """
 abc
 """
-val test6 = "$test1 ${foo()}"
+val test6 = "$test1 ${foo()}"
+
+val test7 = "$test1"
+val test8 = "${foo()}"
+val test9 = "$x"

compiler/testData/ir/irText/expressions/stringTemplates.txt

@@ -3,6 +3,14 @@ FILE /stringTemplates.kt
     BLOCK_BODY
       RETURN type=kotlin.Nothing from='foo(): String'
         CONST String type=kotlin.String value=''
+  PROPERTY public val x: kotlin.Int = 42
+    FIELD PROPERTY_BACKING_FIELD public val x: kotlin.Int = 42
+      EXPRESSION_BODY
+        CONST Int type=kotlin.Int value='42'
+    FUN DEFAULT_PROPERTY_ACCESSOR public fun <get-x>(): kotlin.Int
+      BLOCK_BODY
+        RETURN type=kotlin.Nothing from='<get-x>(): Int'
+          GET_FIELD 'x: Int' type=kotlin.Int origin=null
   PROPERTY public val test1: kotlin.String = ""
     FIELD PROPERTY_BACKING_FIELD public val test1: kotlin.String = ""
       EXPRESSION_BODY
@@ -63,3 +71,30 @@ abc
       BLOCK_BODY
         RETURN type=kotlin.Nothing from='<get-test6>(): String'
           GET_FIELD 'test6: String' type=kotlin.String origin=null
+  PROPERTY public val test7: kotlin.String = ""
+    FIELD PROPERTY_BACKING_FIELD public val test7: kotlin.String = ""
+      EXPRESSION_BODY
+        STRING_CONCATENATION type=kotlin.String
+          CALL '<get-test1>(): String' type=kotlin.String origin=GET_PROPERTY
+    FUN DEFAULT_PROPERTY_ACCESSOR public fun <get-test7>(): kotlin.String
+      BLOCK_BODY
+        RETURN type=kotlin.Nothing from='<get-test7>(): String'
+          GET_FIELD 'test7: String' type=kotlin.String origin=null
+  PROPERTY public val test8: kotlin.String
+    FIELD PROPERTY_BACKING_FIELD public val test8: kotlin.String
+      EXPRESSION_BODY
+        STRING_CONCATENATION type=kotlin.String
+          CALL 'foo(): String' type=kotlin.String origin=null
+    FUN DEFAULT_PROPERTY_ACCESSOR public fun <get-test8>(): kotlin.String
+      BLOCK_BODY
+        RETURN type=kotlin.Nothing from='<get-test8>(): String'
+          GET_FIELD 'test8: String' type=kotlin.String origin=null
+  PROPERTY public val test9: kotlin.String = "42"
+    FIELD PROPERTY_BACKING_FIELD public val test9: kotlin.String = "42"
+      EXPRESSION_BODY
+        STRING_CONCATENATION type=kotlin.String
+          CALL '<get-x>(): Int' type=kotlin.Int origin=GET_PROPERTY
+    FUN DEFAULT_PROPERTY_ACCESSOR public fun <get-test9>(): kotlin.String
+      BLOCK_BODY
+        RETURN type=kotlin.Nothing from='<get-test9>(): String'
+          GET_FIELD 'test9: String' type=kotlin.String origin=null