From a38a23e85f549268974891a896e8ace85665c427 Mon Sep 17 00:00:00 2001
From: Nick Mancuso <nicholas.mancuso13@gmail.com>
Date: Tue, 31 Oct 2023 09:00:29 -0400
Subject: [PATCH] PT-13830: Support Java 21 string template syntax

---
 .../checkstyle/AstTreeStringPrinter.java      |   2 +-
 .../tools/checkstyle/JavaAstVisitor.java      | 158 +++++++
 .../tools/checkstyle/api/TokenTypes.java      |  15 +
 .../grammar/java/JavaLanguageLexer.g4         |  34 +-
 .../grammar/java/JavaLanguageParser.g4        |  19 +
 .../java21/Java21AstRegressionTest.java       |  41 ++
 .../java21/ExpectedStringTemplateBasic.txt    | 421 ++++++++++++++++++
 .../java21/InputStringTemplateBasic.java      |  52 +++
 8 files changed, 738 insertions(+), 4 deletions(-)
 create mode 100644 src/test/java/com/puppycrawl/tools/checkstyle/grammar/java21/Java21AstRegressionTest.java
 create mode 100644 src/test/resources-noncompilable/com/puppycrawl/tools/checkstyle/grammar/java21/ExpectedStringTemplateBasic.txt
 create mode 100644 src/test/resources-noncompilable/com/puppycrawl/tools/checkstyle/grammar/java21/InputStringTemplateBasic.java

diff --git a/src/main/java/com/puppycrawl/tools/checkstyle/AstTreeStringPrinter.java b/src/main/java/com/puppycrawl/tools/checkstyle/AstTreeStringPrinter.java
index 87758b356e27..dbf9e26aa24e 100644
--- a/src/main/java/com/puppycrawl/tools/checkstyle/AstTreeStringPrinter.java
+++ b/src/main/java/com/puppycrawl/tools/checkstyle/AstTreeStringPrinter.java
@@ -162,7 +162,7 @@ public static String printBranch(DetailAST node) {
      * @param ast the root AST node.
      * @return string AST.
      */
-    private static String printTree(DetailAST ast) {
+    public static String printTree(DetailAST ast) {
         final StringBuilder messageBuilder = new StringBuilder(1024);
         DetailAST node = ast;
         while (node != null) {
diff --git a/src/main/java/com/puppycrawl/tools/checkstyle/JavaAstVisitor.java b/src/main/java/com/puppycrawl/tools/checkstyle/JavaAstVisitor.java
index 7e39fd4caeef..5ab8945088e0 100644
--- a/src/main/java/com/puppycrawl/tools/checkstyle/JavaAstVisitor.java
+++ b/src/main/java/com/puppycrawl/tools/checkstyle/JavaAstVisitor.java
@@ -103,6 +103,12 @@ public final class JavaAstVisitor extends JavaLanguageParserBaseVisitor<DetailAs
     /** String representation of the right shift operator. */
     private static final String RIGHT_SHIFT = ">>";
 
+    private static final String QUOTE = "\"";
+
+    private static final String EMBEDDED_EXPRESSION_BEGIN = "\\{";
+
+    private static final String EMBEDDED_EXPRESSION_END = "}";
+
     /**
      * The tokens here are technically expressions, but should
      * not return an EXPR token as their root.
@@ -1533,6 +1539,14 @@ public DetailAstImpl visitPrimaryExp(JavaLanguageParser.PrimaryExpContext ctx) {
         return flattenedTree(ctx);
     }
 
+    @Override
+    public DetailAstImpl visitTemplateExp(JavaLanguageParser.TemplateExpContext ctx) {
+        final DetailAstImpl dot = create(ctx.DOT());
+        dot.addChild(visit(ctx.expr()));
+        dot.addChild(visit(ctx.templateArgument()));
+        return dot;
+    }
+
     @Override
     public DetailAstImpl visitPostfix(JavaLanguageParser.PostfixContext ctx) {
         final DetailAstImpl postfix;
@@ -1742,6 +1756,150 @@ public DetailAstImpl visitPrimitivePrimary(JavaLanguageParser.PrimitivePrimaryCo
         return dot;
     }
 
+    @Override
+    public DetailAstImpl visitTemplateArgument(JavaLanguageParser.TemplateArgumentContext ctx) {
+        final DetailAstImpl templateArgument;
+        if (ctx.template() != null) {
+            templateArgument = visit(ctx.template());
+        }
+        else {
+            templateArgument = flattenedTree(ctx);
+        }
+        return templateArgument;
+    }
+
+    @Override
+    public DetailAstImpl visitStringTemplate(JavaLanguageParser.StringTemplateContext ctx) {
+        final DetailAstImpl begin = buildStringTemplateBeginning(ctx);
+
+        final DetailAstImpl embeddedExp = createImaginary(TokenTypes.EMBEDDED_EXPRESSION);
+        embeddedExp.addChild(visit(ctx.expr()));
+        begin.addChild(embeddedExp);
+
+        ctx.stringTemplateMiddle().stream()
+                .map(this::buildStringTemplateMiddle)
+                .collect(Collectors.toList())
+                .forEach(begin::addChild);
+
+        final DetailAstImpl end = buildStringTemplateEnd(ctx);
+        begin.addChild(end);
+        return begin;
+    }
+
+    private static DetailAstImpl buildStringTemplateBeginning(
+            JavaLanguageParser.StringTemplateContext ctx) {
+
+        final TerminalNode beginContext = ctx.STRING_TEMPLATE_BEGIN();
+        final Token beginToken = beginContext.getSymbol();
+
+        final String stringTemplateBeginText = beginContext.getText();
+        final int childCount = ctx.getChildCount();
+        final int charPositionInLine = beginToken.getCharPositionInLine();
+        final int beginTokenLine = beginToken.getLine();
+
+        final DetailAstImpl begin = buildImaginaryWithDetails(
+                TokenTypes.STRING_TEMPLATE_BEGIN, QUOTE,
+                beginTokenLine, charPositionInLine
+        );
+
+        final int start = QUOTE.length();
+        final int end = stringTemplateBeginText.length() - EMBEDDED_EXPRESSION_BEGIN.length();
+        final String beginContextText = beginContext.getText().substring(start, end);
+
+        final DetailAstImpl beginContent = buildImaginaryWithDetails(
+                TokenTypes.STRING_TEMPLATE_CONTENT, beginContextText,
+                beginTokenLine, charPositionInLine + start
+        );
+        begin.addChild(beginContent);
+
+        final DetailAstImpl embeddedBegin = buildImaginaryWithDetails(
+                TokenTypes.EMBEDDED_EXPRESSION_BEGIN, EMBEDDED_EXPRESSION_BEGIN,
+                beginTokenLine, charPositionInLine + end
+        );
+        begin.addChild(embeddedBegin);
+        return begin;
+    }
+
+    private static DetailAstImpl buildImaginaryWithDetails(
+            int tokenType, String text, int lineNumber, int columnNumber) {
+        final DetailAstImpl imaginary = createImaginary(tokenType);
+        imaginary.setText(text);
+        imaginary.setLineNo(lineNumber);
+        imaginary.setColumnNo(columnNumber);
+        return imaginary;
+    }
+
+    private DetailAstImpl buildStringTemplateMiddle(
+            JavaLanguageParser.StringTemplateMiddleContext middleContext) {
+        final TerminalNode ctx = middleContext.STRING_TEMPLATE_MID();
+        final Token token = ctx.getSymbol();
+        final int charPositionInLine = token.getCharPositionInLine();
+        final int lineNumber = token.getLine();
+        final String text = ctx.getText();
+
+        final DetailAstImpl embeddedEnd = buildImaginaryWithDetails(
+                TokenTypes.EMBEDDED_EXPRESSION_END, EMBEDDED_EXPRESSION_END,
+                lineNumber, charPositionInLine
+        );
+
+        final int startIndex = EMBEDDED_EXPRESSION_END.length();
+        final int endIndex = token.getText().length() - EMBEDDED_EXPRESSION_BEGIN.length();
+        final String contentText = text.substring(startIndex, endIndex);
+
+        final DetailAstImpl content = buildImaginaryWithDetails(
+                TokenTypes.STRING_TEMPLATE_CONTENT, contentText,
+                lineNumber, charPositionInLine + EMBEDDED_EXPRESSION_END.length()
+        );
+        embeddedEnd.addNextSibling(content);
+
+        final DetailAstImpl embeddedBegin = buildImaginaryWithDetails(
+                TokenTypes.EMBEDDED_EXPRESSION_BEGIN, EMBEDDED_EXPRESSION_BEGIN,
+                lineNumber,
+                charPositionInLine + text.length() - EMBEDDED_EXPRESSION_BEGIN.length()
+        );
+        content.addNextSibling(embeddedBegin);
+
+        final DetailAstImpl embeddedExp = createImaginary(TokenTypes.EMBEDDED_EXPRESSION);
+        embeddedExp.addChild(visit(middleContext.expr()));
+        embeddedBegin.addNextSibling(embeddedExp);
+        return embeddedEnd;
+    }
+
+    private static DetailAstImpl buildStringTemplateEnd(
+            JavaLanguageParser.StringTemplateContext ctx) {
+
+        final TerminalNode endContext = ctx.STRING_TEMPLATE_END();
+        final Token endToken = endContext.getSymbol();
+
+        final String stringTemplateEndText = endContext.getText();
+        final int childCount = ctx.getChildCount();
+        final int charPositionInLine = endToken.getCharPositionInLine();
+        final int lineNumber = endToken.getLine();
+
+        final int startIndex = EMBEDDED_EXPRESSION_END.length();
+        final int endIndex = stringTemplateEndText.length() - QUOTE.length();
+        final String endContentContentText = stringTemplateEndText.substring(startIndex, endIndex);
+
+        final DetailAstImpl embeddedEnd = buildImaginaryWithDetails(
+                TokenTypes.EMBEDDED_EXPRESSION_END, EMBEDDED_EXPRESSION_END,
+                lineNumber, charPositionInLine
+        );
+
+        final DetailAstImpl endContent = buildImaginaryWithDetails(
+                TokenTypes.STRING_TEMPLATE_CONTENT, endContentContentText,
+                lineNumber, charPositionInLine + QUOTE.length()
+        );
+        embeddedEnd.addNextSibling(endContent);
+
+        final DetailAstImpl end = buildImaginaryWithDetails(
+                TokenTypes.STRING_TEMPLATE_END, QUOTE,
+                lineNumber,
+                charPositionInLine + stringTemplateEndText.length() - QUOTE.length()
+        );
+        endContent.addNextSibling(end);
+        return embeddedEnd;
+    }
+
     @Override
     public DetailAstImpl visitCreator(JavaLanguageParser.CreatorContext ctx) {
         return flattenedTree(ctx);
diff --git a/src/main/java/com/puppycrawl/tools/checkstyle/api/TokenTypes.java b/src/main/java/com/puppycrawl/tools/checkstyle/api/TokenTypes.java
index e91c987eb742..1143cac7320d 100644
--- a/src/main/java/com/puppycrawl/tools/checkstyle/api/TokenTypes.java
+++ b/src/main/java/com/puppycrawl/tools/checkstyle/api/TokenTypes.java
@@ -6469,6 +6469,21 @@ public final class TokenTypes {
     public static final int RECORD_PATTERN_COMPONENTS =
             JavaLanguageLexer.RECORD_PATTERN_COMPONENTS;
 
+    public static final int STRING_TEMPLATE_BEGIN =
+            JavaLanguageLexer.STRING_TEMPLATE_BEGIN;
+    public static final int STRING_TEMPLATE_MID =
+            JavaLanguageLexer.STRING_TEMPLATE_MID;
+    public static final int STRING_TEMPLATE_END =
+            JavaLanguageLexer.STRING_TEMPLATE_END;
+    public static final int STRING_TEMPLATE_CONTENT =
+            JavaLanguageLexer.STRING_TEMPLATE_CONTENT;
+    public static final int EMBEDDED_EXPRESSION_BEGIN =
+            JavaLanguageLexer.EMBEDDED_EXPRESSION_BEGIN;
+    public static final int EMBEDDED_EXPRESSION =
+            JavaLanguageLexer.EMBEDDED_EXPRESSION;
+    public static final int EMBEDDED_EXPRESSION_END =
+            JavaLanguageLexer.EMBEDDED_EXPRESSION_END;
+
     /** Prevent instantiation. */
     private TokenTypes() {
     }
diff --git a/src/main/resources/com/puppycrawl/tools/checkstyle/grammar/java/JavaLanguageLexer.g4 b/src/main/resources/com/puppycrawl/tools/checkstyle/grammar/java/JavaLanguageLexer.g4
index 945c95db7082..11150a6743f3 100644
--- a/src/main/resources/com/puppycrawl/tools/checkstyle/grammar/java/JavaLanguageLexer.g4
+++ b/src/main/resources/com/puppycrawl/tools/checkstyle/grammar/java/JavaLanguageLexer.g4
@@ -110,7 +110,11 @@ tokens {
 
     LITERAL_NON_SEALED, LITERAL_SEALED, LITERAL_PERMITS,
     PERMITS_CLAUSE, PATTERN_DEF, LITERAL_WHEN,
-    RECORD_PATTERN_DEF, RECORD_PATTERN_COMPONENTS
+    RECORD_PATTERN_DEF, RECORD_PATTERN_COMPONENTS,
+
+    STRING_TEMPLATE_BEGIN, STRING_TEMPLATE_MID, STRING_TEMPLATE_END,
+    STRING_TEMPLATE_CONTENT, EMBEDDED_EXPRESSION_BEGIN, EMBEDDED_EXPRESSION,
+    EMBEDDED_EXPRESSION_END
 }
 
 @header {
@@ -148,6 +152,10 @@ import com.puppycrawl.tools.checkstyle.grammar.CrAwareLexerSimulator;
 
     /** Tracks the starting column of a block comment. */
     int startCol = -1;
+
+    private boolean isTextBlockMode() {
+        return _modeStack.size() > 0 && _modeStack.peek() == TextBlock;
+    }
 }
 
 // Keywords and restricted identifiers
@@ -242,7 +250,14 @@ LITERAL_FALSE:           'false';
 
 CHAR_LITERAL:            '\'' (EscapeSequence | ~['\\\r\n]) '\'';
 
-STRING_LITERAL:          '"' (EscapeSequence | ~["\\\r\n])* '"';
+fragment StringFragment: (EscapeSequence | ~["\\\r\n])*;
+
+STRING_LITERAL:          '"' StringFragment '"';
+
+// explore if we can gather StringFragment and emit a token
+STRING_TEMPLATE_BEGIN:   '"'  StringFragment '\\' '{';
+STRING_TEMPLATE_MID:     '}' StringFragment '\\' '{';
+STRING_TEMPLATE_END:     '}' StringFragment '"';
 
 TEXT_BLOCK_LITERAL_BEGIN: '"' '"' '"' -> pushMode(TextBlock);
 
@@ -403,7 +418,20 @@ fragment Letter
 // Text block lexical mode
 mode TextBlock;
     TEXT_BLOCK_CONTENT
-        : ( TwoDoubleQuotes
+        : TextBlockFragment
+        ;
+
+    TEXT_BLOCK_TEMPLATE_BEGIN
+        : TextBlockFragment '\\' '{' -> pushMode(DEFAULT_MODE);
+
+    TEXT_BLOCK_TEMPLATE_MID
+        : '}' TextBlockFragment '\\' '{';
+
+    TEXT_BLOCK_TEMPLATE_END
+        : '}' TextBlockFragment TEXT_BLOCK_LITERAL_END -> popMode;
+
+    fragment TextBlockFragment
+        :    ( TwoDoubleQuotes
           | OneDoubleQuote
           | Newline
           | ~'"'
diff --git a/src/main/resources/com/puppycrawl/tools/checkstyle/grammar/java/JavaLanguageParser.g4 b/src/main/resources/com/puppycrawl/tools/checkstyle/grammar/java/JavaLanguageParser.g4
index 13452fb5e8aa..d84168cc216b 100644
--- a/src/main/resources/com/puppycrawl/tools/checkstyle/grammar/java/JavaLanguageParser.g4
+++ b/src/main/resources/com/puppycrawl/tools/checkstyle/grammar/java/JavaLanguageParser.g4
@@ -688,6 +688,7 @@ expression
 
 expr
     : primary                                                              #primaryExp
+    | expr DOT templateArgument                                            #templateExp
     | expr bop=DOT id                                                      #refOp
     | expr bop=DOT id LPAREN expressionList? RPAREN                        #methodCall
     | expr bop=DOT LITERAL_THIS                                            #thisExp
@@ -757,6 +758,24 @@ primary
       DOT LITERAL_CLASS                                                    #primitivePrimary
     ;
 
+templateArgument
+    : template
+    | STRING_LITERAL
+    | TEXT_BLOCK_LITERAL_BEGIN TEXT_BLOCK_CONTENT TEXT_BLOCK_LITERAL_END
+    ;
+
+template
+    : stringTemplate
+    ;
+
+stringTemplate
+    : STRING_TEMPLATE_BEGIN expr? stringTemplateMiddle* STRING_TEMPLATE_END
+    ;
+
+stringTemplateMiddle
+    : STRING_TEMPLATE_MID expr?
+    ;
+
 classType
     : (classOrInterfaceType[false] DOT)? annotations[false] id typeArguments?
     ;
diff --git a/src/test/java/com/puppycrawl/tools/checkstyle/grammar/java21/Java21AstRegressionTest.java b/src/test/java/com/puppycrawl/tools/checkstyle/grammar/java21/Java21AstRegressionTest.java
new file mode 100644
index 000000000000..92502ea00d03
--- /dev/null
+++ b/src/test/java/com/puppycrawl/tools/checkstyle/grammar/java21/Java21AstRegressionTest.java
@@ -0,0 +1,41 @@
+///////////////////////////////////////////////////////////////////////////////////////////////
+// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
+// Copyright (C) 2001-2023 the original author or authors.
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+///////////////////////////////////////////////////////////////////////////////////////////////
+
+package com.puppycrawl.tools.checkstyle.grammar.java21;
+
+import org.junit.jupiter.api.Test;
+
+import com.puppycrawl.tools.checkstyle.AbstractTreeTestSupport;
+
+public class Java21AstRegressionTest extends AbstractTreeTestSupport {
+
+    @Override
+    protected String getPackageLocation() {
+        return "com/puppycrawl/tools/checkstyle/grammar/java21";
+    }
+
+    @Test
+    public void testBasicStringTemplate() throws Exception {
+        verifyAst(
+                getNonCompilablePath(
+                        "ExpectedStringTemplateBasic.txt"),
+                getNonCompilablePath(
+                        "InputStringTemplateBasic.java"));
+    }
+}
diff --git a/src/test/resources-noncompilable/com/puppycrawl/tools/checkstyle/grammar/java21/ExpectedStringTemplateBasic.txt b/src/test/resources-noncompilable/com/puppycrawl/tools/checkstyle/grammar/java21/ExpectedStringTemplateBasic.txt
new file mode 100644
index 000000000000..139020aff3be
--- /dev/null
+++ b/src/test/resources-noncompilable/com/puppycrawl/tools/checkstyle/grammar/java21/ExpectedStringTemplateBasic.txt
@@ -0,0 +1,421 @@
+COMPILATION_UNIT -> COMPILATION_UNIT [2:0]
+|--PACKAGE_DEF -> package [2:0]
+|   |--ANNOTATIONS -> ANNOTATIONS [2:47]
+|   |--DOT -> . [2:47]
+|   |   |--DOT -> . [2:39]
+|   |   |   |--DOT -> . [2:28]
+|   |   |   |   |--DOT -> . [2:22]
+|   |   |   |   |   |--DOT -> . [2:11]
+|   |   |   |   |   |   |--IDENT -> com [2:8]
+|   |   |   |   |   |   `--IDENT -> puppycrawl [2:12]
+|   |   |   |   |   `--IDENT -> tools [2:23]
+|   |   |   |   `--IDENT -> checkstyle [2:29]
+|   |   |   `--IDENT -> grammar [2:40]
+|   |   `--IDENT -> java21 [2:48]
+|   `--SEMI -> ; [2:54]
+`--CLASS_DEF -> CLASS_DEF [4:0]
+    |--MODIFIERS -> MODIFIERS [4:0]
+    |   `--LITERAL_PUBLIC -> public [4:0]
+    |--LITERAL_CLASS -> class [4:7]
+    |--IDENT -> InputStringTemplateBasic [4:13]
+    `--OBJBLOCK -> OBJBLOCK [4:38]
+        |--LCURLY -> { [4:38]
+        |--VARIABLE_DEF -> VARIABLE_DEF [5:4]
+        |   |--MODIFIERS -> MODIFIERS [5:4]
+        |   |--TYPE -> TYPE [5:4]
+        |   |   `--LITERAL_INT -> int [5:4]
+        |   |--IDENT -> x [5:8]
+        |   |--ASSIGN -> = [5:10]
+        |   |   `--EXPR -> EXPR [5:12]
+        |   |       `--NUM_INT -> 10 [5:12]
+        |   `--SEMI -> ; [5:14]
+        |--VARIABLE_DEF -> VARIABLE_DEF [6:4]
+        |   |--MODIFIERS -> MODIFIERS [6:4]
+        |   |--TYPE -> TYPE [6:4]
+        |   |   `--LITERAL_INT -> int [6:4]
+        |   |--IDENT -> y [6:8]
+        |   |--ASSIGN -> = [6:10]
+        |   |   `--EXPR -> EXPR [6:12]
+        |   |       `--NUM_INT -> 20 [6:12]
+        |   `--SEMI -> ; [6:14]
+        |--VARIABLE_DEF -> VARIABLE_DEF [9:4]
+        |   |--MODIFIERS -> MODIFIERS [9:4]
+        |   |--TYPE -> TYPE [9:4]
+        |   |   `--IDENT -> String [9:4]
+        |   |--IDENT -> result1 [9:11]
+        |   |--ASSIGN -> = [9:19]
+        |   |   `--EXPR -> EXPR [9:24]
+        |   |       `--DOT -> . [9:24]
+        |   |           |--IDENT -> STR [9:21]
+        |   |           `--STRING_LITERAL -> "" [9:25]
+        |   `--SEMI -> ; [9:27]
+        |--VARIABLE_DEF -> VARIABLE_DEF [12:4]
+        |   |--MODIFIERS -> MODIFIERS [12:4]
+        |   |--TYPE -> TYPE [12:4]
+        |   |   `--IDENT -> String [12:4]
+        |   |--IDENT -> x [12:11]
+        |   |--ASSIGN -> = [12:13]
+        |   |   `--EXPR -> EXPR [12:18]
+        |   |       `--DOT -> . [12:18]
+        |   |           |--IDENT -> STR [12:15]
+        |   |           `--STRING_TEMPLATE_BEGIN -> " [12:19]
+        |   |               |--STRING_TEMPLATE_CONTENT ->  [12:20]
+        |   |               |--EMBEDDED_EXPRESSION_BEGIN -> \{ [12:20]
+        |   |               |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [12:24]
+        |   |               |--EMBEDDED_EXPRESSION_END -> } [12:24]
+        |   |               |--STRING_TEMPLATE_CONTENT ->  [12:25]
+        |   |               `--STRING_TEMPLATE_END -> " [12:25]
+        |   `--SEMI -> ; [12:26]
+        |--VARIABLE_DEF -> VARIABLE_DEF [15:4]
+        |   |--MODIFIERS -> MODIFIERS [15:4]
+        |   |--TYPE -> TYPE [15:4]
+        |   |   `--IDENT -> String [15:4]
+        |   |--IDENT -> result2 [15:11]
+        |   |--ASSIGN -> = [15:19]
+        |   |   `--EXPR -> EXPR [15:24]
+        |   |       `--DOT -> . [15:24]
+        |   |           |--IDENT -> STR [15:21]
+        |   |           `--STRING_TEMPLATE_BEGIN -> " [15:26]
+        |   |               |--STRING_TEMPLATE_CONTENT -> x [15:27]
+        |   |               |--EMBEDDED_EXPRESSION_BEGIN -> \{ [15:28]
+        |   |               |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [15:31]
+        |   |               |   `--IDENT -> x [15:31]
+        |   |               |--EMBEDDED_EXPRESSION_END -> } [15:33]
+        |   |               |--STRING_TEMPLATE_CONTENT -> x [15:34]
+        |   |               `--STRING_TEMPLATE_END -> " [15:35]
+        |   `--SEMI -> ; [15:36]
+        |--VARIABLE_DEF -> VARIABLE_DEF [18:4]
+        |   |--MODIFIERS -> MODIFIERS [18:4]
+        |   |--TYPE -> TYPE [18:4]
+        |   |   `--IDENT -> String [18:4]
+        |   |--IDENT -> result3 [18:11]
+        |   |--ASSIGN -> = [18:19]
+        |   |   `--EXPR -> EXPR [18:24]
+        |   |       `--DOT -> . [18:24]
+        |   |           |--IDENT -> STR [18:21]
+        |   |           `--STRING_TEMPLATE_BEGIN -> " [18:26]
+        |   |               |--STRING_TEMPLATE_CONTENT ->  [18:27]
+        |   |               |--EMBEDDED_EXPRESSION_BEGIN -> \{ [18:27]
+        |   |               |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [18:31]
+        |   |               |   `--METHOD_CALL -> ( [18:31]
+        |   |               |       |--IDENT -> y [18:30]
+        |   |               |       |--ELIST -> ELIST [18:33]
+        |   |               |       |   `--EXPR -> EXPR [18:33]
+        |   |               |       |       `--METHOD_CALL -> ( [18:33]
+        |   |               |       |           |--IDENT -> y [18:32]
+        |   |               |       |           |--ELIST -> ELIST [18:34]
+        |   |               |       |           |   `--EXPR -> EXPR [18:34]
+        |   |               |       |           |       `--STRING_LITERAL -> "y" [18:34]
+        |   |               |       |           `--RPAREN -> ) [18:37]
+        |   |               |       `--RPAREN -> ) [18:38]
+        |   |               |--EMBEDDED_EXPRESSION_END -> } [18:40]
+        |   |               |--STRING_TEMPLATE_CONTENT ->  [18:41]
+        |   |               `--STRING_TEMPLATE_END -> " [18:41]
+        |   `--SEMI -> ; [18:42]
+        |--VARIABLE_DEF -> VARIABLE_DEF [21:4]
+        |   |--MODIFIERS -> MODIFIERS [21:4]
+        |   |--TYPE -> TYPE [21:4]
+        |   |   `--IDENT -> String [21:4]
+        |   |--IDENT -> result4 [21:11]
+        |   |--ASSIGN -> = [21:19]
+        |   |   `--EXPR -> EXPR [21:36]
+        |   |       `--PLUS -> + [21:36]
+        |   |           |--DOT -> . [21:24]
+        |   |           |   |--IDENT -> STR [21:21]
+        |   |           |   `--STRING_TEMPLATE_BEGIN -> " [21:26]
+        |   |           |       |--STRING_TEMPLATE_CONTENT ->  [21:27]
+        |   |           |       |--EMBEDDED_EXPRESSION_BEGIN -> \{ [21:27]
+        |   |           |       |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [21:30]
+        |   |           |       |   `--IDENT -> x [21:30]
+        |   |           |       |--EMBEDDED_EXPRESSION_END -> } [21:32]
+        |   |           |       |--STRING_TEMPLATE_CONTENT ->  [21:33]
+        |   |           |       `--STRING_TEMPLATE_END -> " [21:33]
+        |   |           `--DOT -> . [21:41]
+        |   |               |--IDENT -> STR [21:38]
+        |   |               `--STRING_TEMPLATE_BEGIN -> " [21:43]
+        |   |                   |--STRING_TEMPLATE_CONTENT ->  [21:44]
+        |   |                   |--EMBEDDED_EXPRESSION_BEGIN -> \{ [21:44]
+        |   |                   |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [21:47]
+        |   |                   |   `--IDENT -> y [21:47]
+        |   |                   |--EMBEDDED_EXPRESSION_END -> } [21:49]
+        |   |                   |--STRING_TEMPLATE_CONTENT ->  [21:50]
+        |   |                   `--STRING_TEMPLATE_END -> " [21:50]
+        |   `--SEMI -> ; [21:51]
+        |--VARIABLE_DEF -> VARIABLE_DEF [24:4]
+        |   |--MODIFIERS -> MODIFIERS [24:4]
+        |   |--TYPE -> TYPE [24:4]
+        |   |   `--IDENT -> String [24:4]
+        |   |--IDENT -> result5 [24:11]
+        |   |--ASSIGN -> = [24:19]
+        |   |   `--EXPR -> EXPR [24:44]
+        |   |       `--PLUS -> + [24:44]
+        |   |           |--DOT -> . [24:24]
+        |   |           |   |--IDENT -> STR [24:21]
+        |   |           |   `--STRING_TEMPLATE_BEGIN -> " [24:26]
+        |   |           |       |--STRING_TEMPLATE_CONTENT ->  [24:27]
+        |   |           |       |--EMBEDDED_EXPRESSION_BEGIN -> \{ [24:27]
+        |   |           |       |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [24:31]
+        |   |           |       |   `--METHOD_CALL -> ( [24:31]
+        |   |           |       |       |--IDENT -> y [24:30]
+        |   |           |       |       |--ELIST -> ELIST [24:33]
+        |   |           |       |       |   `--EXPR -> EXPR [24:33]
+        |   |           |       |       |       `--METHOD_CALL -> ( [24:33]
+        |   |           |       |       |           |--IDENT -> y [24:32]
+        |   |           |       |       |           |--ELIST -> ELIST [24:34]
+        |   |           |       |       |           |   `--EXPR -> EXPR [24:34]
+        |   |           |       |       |           |       `--STRING_LITERAL -> "y" [24:34]
+        |   |           |       |       |           `--RPAREN -> ) [24:37]
+        |   |           |       |       `--RPAREN -> ) [24:38]
+        |   |           |       |--EMBEDDED_EXPRESSION_END -> } [24:40]
+        |   |           |       |--STRING_TEMPLATE_CONTENT ->  [24:41]
+        |   |           |       `--STRING_TEMPLATE_END -> " [24:41]
+        |   |           `--DOT -> . [24:49]
+        |   |               |--IDENT -> STR [24:46]
+        |   |               `--STRING_TEMPLATE_BEGIN -> " [24:51]
+        |   |                   |--STRING_TEMPLATE_CONTENT ->  [24:52]
+        |   |                   |--EMBEDDED_EXPRESSION_BEGIN -> \{ [24:52]
+        |   |                   |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [24:56]
+        |   |                   |   `--METHOD_CALL -> ( [24:56]
+        |   |                   |       |--IDENT -> y [24:55]
+        |   |                   |       |--ELIST -> ELIST [24:58]
+        |   |                   |       |   `--EXPR -> EXPR [24:58]
+        |   |                   |       |       `--METHOD_CALL -> ( [24:58]
+        |   |                   |       |           |--IDENT -> y [24:57]
+        |   |                   |       |           |--ELIST -> ELIST [24:59]
+        |   |                   |       |           |   `--EXPR -> EXPR [24:59]
+        |   |                   |       |           |       `--STRING_LITERAL -> "y" [24:59]
+        |   |                   |       |           `--RPAREN -> ) [24:62]
+        |   |                   |       `--RPAREN -> ) [24:63]
+        |   |                   |--EMBEDDED_EXPRESSION_END -> } [24:65]
+        |   |                   |--STRING_TEMPLATE_CONTENT ->  [24:66]
+        |   |                   `--STRING_TEMPLATE_END -> " [24:66]
+        |   `--SEMI -> ; [24:67]
+        |--VARIABLE_DEF -> VARIABLE_DEF [27:4]
+        |   |--MODIFIERS -> MODIFIERS [27:4]
+        |   |--TYPE -> TYPE [27:4]
+        |   |   `--IDENT -> String [27:4]
+        |   |--IDENT -> result6 [27:11]
+        |   |--ASSIGN -> = [27:19]
+        |   |   `--EXPR -> EXPR [27:36]
+        |   |       `--PLUS -> + [27:36]
+        |   |           |--DOT -> . [27:24]
+        |   |           |   |--IDENT -> STR [27:21]
+        |   |           |   `--STRING_TEMPLATE_BEGIN -> " [27:26]
+        |   |           |       |--STRING_TEMPLATE_CONTENT ->  [27:27]
+        |   |           |       |--EMBEDDED_EXPRESSION_BEGIN -> \{ [27:27]
+        |   |           |       |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [27:30]
+        |   |           |       |   `--IDENT -> x [27:30]
+        |   |           |       |--EMBEDDED_EXPRESSION_END -> } [27:32]
+        |   |           |       |--STRING_TEMPLATE_CONTENT ->  [27:33]
+        |   |           |       `--STRING_TEMPLATE_END -> " [27:33]
+        |   |           `--DOT -> . [27:41]
+        |   |               |--IDENT -> STR [27:38]
+        |   |               `--STRING_TEMPLATE_BEGIN -> " [27:43]
+        |   |                   |--STRING_TEMPLATE_CONTENT ->  [27:44]
+        |   |                   |--EMBEDDED_EXPRESSION_BEGIN -> \{ [27:44]
+        |   |                   |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [27:47]
+        |   |                   |   `--IDENT -> y [27:47]
+        |   |                   |--EMBEDDED_EXPRESSION_END -> } [27:49]
+        |   |                   |--STRING_TEMPLATE_CONTENT ->  [27:50]
+        |   |                   `--STRING_TEMPLATE_END -> " [27:50]
+        |   `--SEMI -> ; [27:51]
+        |--VARIABLE_DEF -> VARIABLE_DEF [30:4]
+        |   |--MODIFIERS -> MODIFIERS [30:4]
+        |   |--TYPE -> TYPE [30:4]
+        |   |   `--IDENT -> String [30:4]
+        |   |--IDENT -> result7 [30:11]
+        |   |--ASSIGN -> = [30:19]
+        |   |   `--EXPR -> EXPR [30:24]
+        |   |       `--DOT -> . [30:24]
+        |   |           |--IDENT -> STR [30:21]
+        |   |           `--STRING_TEMPLATE_BEGIN -> " [30:26]
+        |   |               |--STRING_TEMPLATE_CONTENT ->  [30:27]
+        |   |               |--EMBEDDED_EXPRESSION_BEGIN -> \{ [30:27]
+        |   |               |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [30:32]
+        |   |               |   `--PLUS -> + [30:32]
+        |   |               |       |--IDENT -> x [30:30]
+        |   |               |       `--IDENT -> y [30:34]
+        |   |               |--EMBEDDED_EXPRESSION_END -> } [30:36]
+        |   |               |--STRING_TEMPLATE_CONTENT ->  [30:37]
+        |   |               `--STRING_TEMPLATE_END -> " [30:37]
+        |   `--SEMI -> ; [30:38]
+        |--VARIABLE_DEF -> VARIABLE_DEF [33:4]
+        |   |--MODIFIERS -> MODIFIERS [33:4]
+        |   |--TYPE -> TYPE [33:4]
+        |   |   `--IDENT -> String [33:4]
+        |   |--IDENT -> result8 [33:11]
+        |   |--ASSIGN -> = [33:19]
+        |   |   `--EXPR -> EXPR [33:24]
+        |   |       `--DOT -> . [33:24]
+        |   |           |--IDENT -> STR [33:21]
+        |   |           `--STRING_TEMPLATE_BEGIN -> " [33:26]
+        |   |               |--STRING_TEMPLATE_CONTENT -> hey  [33:27]
+        |   |               |--EMBEDDED_EXPRESSION_BEGIN -> \{ [33:31]
+        |   |               |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [33:44]
+        |   |               |   `--PLUS -> + [33:44]
+        |   |               |       |--METHOD_CALL -> ( [33:35]
+        |   |               |       |   |--IDENT -> y [33:34]
+        |   |               |       |   |--ELIST -> ELIST [33:37]
+        |   |               |       |   |   `--EXPR -> EXPR [33:37]
+        |   |               |       |   |       `--METHOD_CALL -> ( [33:37]
+        |   |               |       |   |           |--IDENT -> y [33:36]
+        |   |               |       |   |           |--ELIST -> ELIST [33:38]
+        |   |               |       |   |           |   `--EXPR -> EXPR [33:38]
+        |   |               |       |   |           |       `--STRING_LITERAL -> "y" [33:38]
+        |   |               |       |   |           `--RPAREN -> ) [33:41]
+        |   |               |       |   `--RPAREN -> ) [33:42]
+        |   |               |       `--METHOD_CALL -> ( [33:47]
+        |   |               |           |--IDENT -> y [33:46]
+        |   |               |           |--ELIST -> ELIST [33:49]
+        |   |               |           |   `--EXPR -> EXPR [33:49]
+        |   |               |           |       `--METHOD_CALL -> ( [33:49]
+        |   |               |           |           |--IDENT -> y [33:48]
+        |   |               |           |           |--ELIST -> ELIST [33:50]
+        |   |               |           |           |   `--EXPR -> EXPR [33:50]
+        |   |               |           |           |       `--STRING_LITERAL -> "y" [33:50]
+        |   |               |           |           `--RPAREN -> ) [33:53]
+        |   |               |           `--RPAREN -> ) [33:54]
+        |   |               |--EMBEDDED_EXPRESSION_END -> } [33:56]
+        |   |               |--STRING_TEMPLATE_CONTENT ->  there [33:57]
+        |   |               `--STRING_TEMPLATE_END -> " [33:63]
+        |   `--SEMI -> ; [33:64]
+        |--VARIABLE_DEF -> VARIABLE_DEF [36:4]
+        |   |--MODIFIERS -> MODIFIERS [36:4]
+        |   |--TYPE -> TYPE [36:4]
+        |   |   `--IDENT -> String [36:4]
+        |   |--IDENT -> result9 [36:11]
+        |   |--ASSIGN -> = [36:19]
+        |   |   `--EXPR -> EXPR [36:24]
+        |   |       `--DOT -> . [36:24]
+        |   |           |--IDENT -> STR [36:21]
+        |   |           `--STRING_TEMPLATE_BEGIN -> " [36:26]
+        |   |               |--STRING_TEMPLATE_CONTENT -> hey  [36:27]
+        |   |               |--EMBEDDED_EXPRESSION_BEGIN -> \{ [36:31]
+        |   |               |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [37:22]
+        |   |               |   `--PLUS -> + [37:22]
+        |   |               |       |--METHOD_CALL -> ( [37:13]
+        |   |               |       |   |--IDENT -> y [37:12]
+        |   |               |       |   |--ELIST -> ELIST [37:15]
+        |   |               |       |   |   `--EXPR -> EXPR [37:15]
+        |   |               |       |   |       `--METHOD_CALL -> ( [37:15]
+        |   |               |       |   |           |--IDENT -> y [37:14]
+        |   |               |       |   |           |--ELIST -> ELIST [37:16]
+        |   |               |       |   |           |   `--EXPR -> EXPR [37:16]
+        |   |               |       |   |           |       `--STRING_LITERAL -> "y" [37:16]
+        |   |               |       |   |           `--RPAREN -> ) [37:19]
+        |   |               |       |   `--RPAREN -> ) [37:20]
+        |   |               |       `--METHOD_CALL -> ( [37:25]
+        |   |               |           |--IDENT -> y [37:24]
+        |   |               |           |--ELIST -> ELIST [37:27]
+        |   |               |           |   `--EXPR -> EXPR [37:27]
+        |   |               |           |       `--METHOD_CALL -> ( [37:27]
+        |   |               |           |           |--IDENT -> y [37:26]
+        |   |               |           |           |--ELIST -> ELIST [37:28]
+        |   |               |           |           |   `--EXPR -> EXPR [37:28]
+        |   |               |           |           |       `--STRING_LITERAL -> "y" [37:28]
+        |   |               |           |           `--RPAREN -> ) [37:31]
+        |   |               |           `--RPAREN -> ) [37:32]
+        |   |               |--EMBEDDED_EXPRESSION_END -> } [38:12]
+        |   |               |--STRING_TEMPLATE_CONTENT ->  there [38:13]
+        |   |               `--STRING_TEMPLATE_END -> " [38:19]
+        |   `--SEMI -> ; [38:20]
+        |--VARIABLE_DEF -> VARIABLE_DEF [41:4]
+        |   |--MODIFIERS -> MODIFIERS [41:4]
+        |   |--TYPE -> TYPE [41:4]
+        |   |   `--IDENT -> String [41:4]
+        |   |--IDENT -> result10 [41:11]
+        |   |--ASSIGN -> = [41:20]
+        |   |   `--EXPR -> EXPR [41:25]
+        |   |       `--DOT -> . [41:25]
+        |   |           |--IDENT -> STR [41:22]
+        |   |           `--STRING_TEMPLATE_BEGIN -> " [41:27]
+        |   |               |--STRING_TEMPLATE_CONTENT -> hey  [41:28]
+        |   |               |--EMBEDDED_EXPRESSION_BEGIN -> \{ [41:32]
+        |   |               |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [42:22]
+        |   |               |   `--PLUS -> + [42:22]
+        |   |               |       |--METHOD_CALL -> ( [42:13]
+        |   |               |       |   |--IDENT -> y [42:12]
+        |   |               |       |   |--ELIST -> ELIST [42:15]
+        |   |               |       |   |   `--EXPR -> EXPR [42:15]
+        |   |               |       |   |       `--METHOD_CALL -> ( [42:15]
+        |   |               |       |   |           |--IDENT -> y [42:14]
+        |   |               |       |   |           |--ELIST -> ELIST [42:16]
+        |   |               |       |   |           |   `--EXPR -> EXPR [42:16]
+        |   |               |       |   |           |       `--STRING_LITERAL -> "y" [42:16]
+        |   |               |       |   |           `--RPAREN -> ) [42:19]
+        |   |               |       |   `--RPAREN -> ) [42:20]
+        |   |               |       `--METHOD_CALL -> ( [42:25]
+        |   |               |           |--IDENT -> y [42:24]
+        |   |               |           |--ELIST -> ELIST [42:27]
+        |   |               |           |   `--EXPR -> EXPR [42:27]
+        |   |               |           |       `--METHOD_CALL -> ( [42:27]
+        |   |               |           |           |--IDENT -> y [42:26]
+        |   |               |           |           |--ELIST -> ELIST [42:28]
+        |   |               |           |           |   `--EXPR -> EXPR [42:28]
+        |   |               |           |           |       `--STRING_LITERAL -> "y" [42:28]
+        |   |               |           |           `--RPAREN -> ) [42:31]
+        |   |               |           `--RPAREN -> ) [42:32]
+        |   |               |--EMBEDDED_EXPRESSION_END -> } [43:12]
+        |   |               |--STRING_TEMPLATE_CONTENT ->  there  [44:13]
+        |   |               |--EMBEDDED_EXPRESSION_BEGIN -> \{ [43:20]
+        |   |               |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [45:12]
+        |   |               |   `--PLUS -> + [45:12]
+        |   |               |       |--PLUS -> + [44:22]
+        |   |               |       |   |--METHOD_CALL -> ( [44:13]
+        |   |               |       |   |   |--IDENT -> y [44:12]
+        |   |               |       |   |   |--ELIST -> ELIST [44:15]
+        |   |               |       |   |   |   `--EXPR -> EXPR [44:15]
+        |   |               |       |   |   |       `--METHOD_CALL -> ( [44:15]
+        |   |               |       |   |   |           |--IDENT -> y [44:14]
+        |   |               |       |   |   |           |--ELIST -> ELIST [44:16]
+        |   |               |       |   |   |           |   `--EXPR -> EXPR [44:16]
+        |   |               |       |   |   |           |       `--STRING_LITERAL -> "y" [44:16]
+        |   |               |       |   |   |           `--RPAREN -> ) [44:19]
+        |   |               |       |   |   `--RPAREN -> ) [44:20]
+        |   |               |       |   `--METHOD_CALL -> ( [44:25]
+        |   |               |       |       |--IDENT -> y [44:24]
+        |   |               |       |       |--ELIST -> ELIST [44:27]
+        |   |               |       |       |   `--EXPR -> EXPR [44:27]
+        |   |               |       |       |       `--METHOD_CALL -> ( [44:27]
+        |   |               |       |       |           |--IDENT -> y [44:26]
+        |   |               |       |       |           |--ELIST -> ELIST [44:28]
+        |   |               |       |       |           |   `--EXPR -> EXPR [44:28]
+        |   |               |       |       |           |       `--STRING_LITERAL -> "y" [44:28]
+        |   |               |       |       |           `--RPAREN -> ) [44:31]
+        |   |               |       |       `--RPAREN -> ) [44:32]
+        |   |               |       `--DOT -> . [45:17]
+        |   |               |           |--IDENT -> STR [45:14]
+        |   |               |           `--STRING_TEMPLATE_BEGIN -> " [45:18]
+        |   |               |               |--STRING_TEMPLATE_CONTENT -> x [45:19]
+        |   |               |               |--EMBEDDED_EXPRESSION_BEGIN -> \{ [45:20]
+        |   |               |               |--EMBEDDED_EXPRESSION -> EMBEDDED_EXPRESSION [45:23]
+        |   |               |               |   `--IDENT -> x [45:23]
+        |   |               |               |--EMBEDDED_EXPRESSION_END -> } [45:25]
+        |   |               |               |--STRING_TEMPLATE_CONTENT -> x [45:26]
+        |   |               |               `--STRING_TEMPLATE_END -> " [45:27]
+        |   |               |--EMBEDDED_EXPRESSION_END -> } [46:12]
+        |   |               |--STRING_TEMPLATE_CONTENT ->  [46:13]
+        |   |               `--STRING_TEMPLATE_END -> " [46:13]
+        |   `--SEMI -> ; [46:14]
+        |--METHOD_DEF -> METHOD_DEF [49:4]
+        |   |--MODIFIERS -> MODIFIERS [49:4]
+        |   |   |--LITERAL_PRIVATE -> private [49:4]
+        |   |   `--LITERAL_STATIC -> static [49:12]
+        |   |--TYPE -> TYPE [49:19]
+        |   |   `--IDENT -> String [49:19]
+        |   |--IDENT -> y [49:26]
+        |   |--LPAREN -> ( [49:27]
+        |   |--PARAMETERS -> PARAMETERS [49:28]
+        |   |   `--PARAMETER_DEF -> PARAMETER_DEF [49:28]
+        |   |       |--MODIFIERS -> MODIFIERS [49:28]
+        |   |       |--TYPE -> TYPE [49:28]
+        |   |       |   `--IDENT -> String [49:28]
+        |   |       `--IDENT -> y [49:35]
+        |   |--RPAREN -> ) [49:36]
+        |   `--SLIST -> { [49:38]
+        |       |--LITERAL_RETURN -> return [50:8]
+        |       |   |--EXPR -> EXPR [50:15]
+        |       |   |   `--STRING_LITERAL -> "y" [50:15]
+        |       |   `--SEMI -> ; [50:18]
+        |       `--RCURLY -> } [51:4]
+        `--RCURLY -> } [52:0]
diff --git a/src/test/resources-noncompilable/com/puppycrawl/tools/checkstyle/grammar/java21/InputStringTemplateBasic.java b/src/test/resources-noncompilable/com/puppycrawl/tools/checkstyle/grammar/java21/InputStringTemplateBasic.java
new file mode 100644
index 000000000000..2e92ac0bccc4
--- /dev/null
+++ b/src/test/resources-noncompilable/com/puppycrawl/tools/checkstyle/grammar/java21/InputStringTemplateBasic.java
@@ -0,0 +1,52 @@
+//non-compiled with javac: Compilable with Java21
+package com.puppycrawl.tools.checkstyle.grammar.java21;
+
+public class InputStringTemplateBasic {
+    int x = 10;
+    int y = 20;
+
+    // most basic example, empty string template expression
+    String result1 = STR."";
+
+    // no content, no expression
+    String x = STR."\{  }";
+
+    // simple single value interpolation
+    String result2 = STR. "x\{ x }x";
+
+    // simple single value interpolation with a method call
+    String result3 = STR. "\{ y(y("y")) }";
+
+    // bit more complex example, multiple interpolations
+    String result4 = STR. "\{ x }"  + STR. "\{ y }";
+
+    // bit more complex example, multiple interpolations with method calls
+    String result5 = STR. "\{ y(y("y")) }"  + STR. "\{ y(y("y")) }";
+
+    // string template concatenation
+    String result6 = STR. "\{ x }"  + STR. "\{ y }";
+
+    // concatentation in embedded expression
+    String result7 = STR. "\{ x + y }";
+
+    // concatentation in embedded expression with method calls
+    String result8 = STR. "hey \{ y(y("y")) + y(y("y")) } there";
+
+    // multiple lines
+    String result9 = STR. "hey \{
+            y(y("y")) + y(y("y"))
+            } there";
+
+    // multiple lines with many expressions
+    String result10 = STR. "hey \{
+            y(y("y")) + y(y("y"))
+            } there \{
+            y(y("y")) + y(y("y"))
+            + STR."x\{ x }x"
+            }";
+
+
+    private static String y(String y) {
+        return "y";
+    }
+}