[FIR] Fix disappeared ILLEGAL_ESCAPE

^KT-59950 Fixed

compiler/fir/raw-fir/raw-fir.common/src/org/jetbrains/kotlin/fir/builder/AbstractRawFirBuilder.kt

@@ -514,8 +514,15 @@ abstract class AbstractRawFirBuilder<T>(val baseSession: FirSession, val context
                         }
                         ESCAPE_STRING_TEMPLATE_ENTRY -> {
                             sb.append(entry.unescapedValue)
-                            buildConstExpression(
-                                entry.toFirSourceElement(), ConstantValueKind.String, entry.unescapedValue, setType = false
+                            val characterWithDiagnostic = escapedStringToCharacter(entry.asText)
+                            buildConstOrErrorExpression(
+                                entry.toFirSourceElement(),
+                                ConstantValueKind.Char,
+                                characterWithDiagnostic.value,
+                                ConeSimpleDiagnostic(
+                                    "Incorrect character: ${entry.asText}",
+                                    characterWithDiagnostic.getDiagnostic() ?: DiagnosticKind.IllegalConstExpression
+                                )
                             )
                         }
                         SHORT_STRING_TEMPLATE_ENTRY, LONG_STRING_TEMPLATE_ENTRY -> {
@@ -533,8 +540,9 @@ abstract class AbstractRawFirBuilder<T>(val baseSession: FirSession, val context
                 }
             }
             source = base?.toFirSourceElement()
-            // Fast-pass if there is no non-const string expressions
-            if (!hasExpressions) return buildConstExpression(source, ConstantValueKind.String, sb.toString(), setType = false)
+            // Fast-pass if there is no errors and non-const string expressions
+            if (!hasExpressions && !argumentList.arguments.any { it is FirErrorExpression })
+                return buildConstExpression(source, ConstantValueKind.String, sb.toString(), setType = false)
         }
     }
 

compiler/testData/diagnostics/tests/StringTemplates.fir.kt

@@ -1,22 +0,0 @@
-fun demo() {
-  val abc = 1
-  val a = ""
-  val asd = 1
-  val bar = 5
-  fun map(f :  () -> Any?) : Int  = 1
-  fun buzz(f :  () -> Any?) : Int  = 1
-  val sdf = 1
-  val foo = 3;
-    "$abc"
-    "$"
-    "$.$.asdf$\t"
-    "asd\$"
-    "asd$a\x"
-    "asd$a$asd$ $<!UNRESOLVED_REFERENCE!>xxx<!>"
-    "fosdfasdo${1 + bar + 100}}sdsdfgdsfsdf"
-    "foo${bar + map {foo}}sdfsdf"
-    "foo${bar + map { "foo" }}sdfsdf"
-    "foo${bar + map {
-      "foo$sdf${ buzz{}}" }}sdfsdf"
-    "a\u \u0 \u00 \u000 \u0000 \u0AaA \u0AAz.length( ) + \u0022b"
-}

compiler/testData/diagnostics/tests/StringTemplates.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 fun demo() {
   val abc = 1
   val a = ""