Prepend indent for user-provided multi-line compilation messages

api/src/main/kotlin/io/spine/protodata/Compilation.kt

@@ -33,11 +33,13 @@ import io.spine.protodata.Compilation.ERROR_EXIT_CODE
 import io.spine.protodata.Compilation.error
 import io.spine.protodata.ast.Span
 import io.spine.protodata.ast.toJava
+import io.spine.string.Indent
+import io.spine.string.Separator
+import io.spine.string.indent
 import java.io.File
 import kotlin.system.exitProcess
 import io.spine.protodata.ast.File as PFile
 
-
 /**
  * Provides functions to report compilation errors and warnings.
  *
@@ -140,7 +142,7 @@ public object Compilation {
 
     @VisibleForTesting
     internal fun errorMessage(file: File, line: Int, column: Int, message: String) =
-        "$ERROR_PREFIX ${file.maybeUri()}:$line:$column: $message"
+        indentedMessage(ERROR_PREFIX, file, line, column, message)
 
     /**
      * Prints the warning diagnostics to [System.out].
@@ -191,7 +193,48 @@ public object Compilation {
 
     @VisibleForTesting
     internal fun warningMessage(file: File, line: Int, column: Int, message: String) =
-        "$WARNING_PREFIX ${file.maybeUri()}:$line:$column: $message"
+        indentedMessage(WARNING_PREFIX, file, line, column, message)
+
+    /**
+     * Constructs a formatted compilation message with indentation
+     * for multi-line user messages.
+     *
+     * The returned string consists of:
+     *
+     * 1. The specified [prefix] followed by the file URI or path, line, and column.
+     * 2. The first line of the [message] appended directly to the header.
+     * 3. Any subsequent lines of the [message], each indented under the header
+     *    by the length of the [prefix] plus one space.
+     *
+     * @throws IllegalArgumentException if [prefix] is blank.
+     */
+    @VisibleForTesting
+    internal fun indentedMessage(
+        prefix: String,
+        file: File,
+        line: Int,
+        column: Int,
+        message: String
+    ): String {
+        require(prefix.isNotBlank()) {
+            "The compilation message must have a non-empty prefix specified."
+        }
+
+        val messageLines = message.lines()
+        val messageHeader = messageLines.first()
+
+        val indent = Indent(prefix.length + 1)
+        val indentedBody = messageLines.drop(1)
+            .indent(indent, level = 1)
+
+        return buildString {
+            append("$prefix ${file.maybeUri()}:$line:$column: $messageHeader")
+            if (indentedBody.isNotEmpty()) {
+                append(Separator.nl())
+                append(indentedBody)
+            }
+        }
+    }
 
     /**
      * The exception thrown by [Compilation.error] when the testing mode is on.

api/src/test/kotlin/io/spine/protodata/CompilationSpec.kt

@@ -26,6 +26,7 @@
 
 package io.spine.protodata
 
+import io.kotest.matchers.shouldBe
 import io.kotest.matchers.string.shouldContain
 import io.kotest.matchers.string.shouldNotContain
 import io.kotest.matchers.string.shouldStartWith
@@ -34,10 +35,13 @@ import io.spine.protodata.Compilation.ERROR_PREFIX
 import io.spine.protodata.Compilation.WARNING_PREFIX
 import io.spine.protodata.ast.Span
 import io.spine.protodata.ast.toAbsoluteFile
+import io.spine.string.ti
+import io.spine.string.tm
 import io.spine.testing.TestValues
 import java.io.File
 import java.nio.file.Paths
 import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Nested
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.assertDoesNotThrow
 import org.junit.jupiter.api.assertThrows
@@ -161,6 +165,73 @@ internal class CompilationSpec {
             Compilation.check(condition = true, file, span) { msg }
         }
     }
+
+    @Nested inner class
+    `when indenting a user message` {
+
+        private val file = File("with_error.proto")
+        private val prefix = "m:"
+        private val line = 1
+        private val column = 1
+
+        @Test
+        fun `use the prefix length as a number of spaces`() {
+            val message = """
+                The file contains one or more mistakes.
+                Mistake #1: illegal beginning.
+                Mistake #2: illegal ending.
+            """.ti()
+
+            val result = Compilation.indentedMessage(prefix, file, line, column, message)
+            val expected = """
+                m: with_error.proto:1:1: The file contains one or more mistakes.
+                   Mistake #1: illegal beginning.
+                   Mistake #2: illegal ending.
+            """.ti()
+
+            result shouldBe expected
+        }
+
+        @Test
+        fun `throw when given an empty prefix`() {
+            assertThrows<IllegalArgumentException> {
+                Compilation.indentedMessage(prefix = "", file, line, column, message = "")
+            }
+        }
+
+        @Test
+        fun `do not append trailing lines for one-line messages`() {
+            val message = "The file contains one or more mistakes."
+            val result = Compilation.indentedMessage(prefix, file, line, column, message)
+            result shouldBe "m: with_error.proto:1:1: The file contains one or more mistakes."
+        }
+
+        @Test
+        fun `do nothing for empty messages`() {
+            val result = Compilation.indentedMessage(prefix, file, line, column, message = "")
+            result shouldBe "m: with_error.proto:1:1: "
+        }
+
+        @Test
+        fun `preserve original blank lines and whitespaces`() {
+            val message = """
+                First line.
+
+                Third line after blank.
+                  Fourth line with its own whitespaces.
+            """.ti()
+
+            val result = Compilation.indentedMessage(prefix, file, line, column, message)
+            val expected = """
+                |m: with_error.proto:1:1: First line.
+                |   
+                |   Third line after blank.
+                |     Fourth line with its own whitespaces.
+            """.tm()
+
+            result shouldBe expected
+        }
+    }
 }
 
 private fun File.uriRef(): String {

buildSrc/src/main/kotlin/io/spine/dependency/local/Base.kt

@@ -33,8 +33,8 @@ package io.spine.dependency.local
  */
 @Suppress("ConstPropertyName")
 object Base {
-    const val version = "2.0.0-SNAPSHOT.316"
-    const val versionForBuildScript = "2.0.0-SNAPSHOT.316"
+    const val version = "2.0.0-SNAPSHOT.318"
+    const val versionForBuildScript = "2.0.0-SNAPSHOT.318"
     const val group = Spine.group
     const val artifact = "spine-base"
     const val lib = "$group:$artifact:$version"

dependencies.md

@@ -1,6 +1,6 @@
 
 
-# Dependencies of `io.spine.protodata:protodata-api:0.95.0`
+# Dependencies of `io.spine.protodata:protodata-api:0.95.1`
 
 ## Runtime
 1.  **Group** : com.fasterxml.jackson. **Name** : jackson-bom. **Version** : 2.18.3.
@@ -1110,12 +1110,12 @@
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Thu May 08 19:15:02 WEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Fri May 16 16:39:56 CEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.protodata:protodata-api-tests:0.95.0`
+# Dependencies of `io.spine.protodata:protodata-api-tests:0.95.1`
 
 ## Runtime
 1.  **Group** : org.jetbrains. **Name** : annotations. **Version** : 13.0.
@@ -1956,12 +1956,12 @@ This report was generated on **Thu May 08 19:15:02 WEST 2025** using [Gradle-Lic
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Thu May 08 19:15:02 WEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Fri May 16 16:39:56 CEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.protodata:protodata-backend:0.95.0`
+# Dependencies of `io.spine.protodata:protodata-backend:0.95.1`
 
 ## Runtime
 1.  **Group** : com.fasterxml.jackson. **Name** : jackson-bom. **Version** : 2.18.3.
@@ -3071,12 +3071,12 @@ This report was generated on **Thu May 08 19:15:02 WEST 2025** using [Gradle-Lic
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Thu May 08 19:15:03 WEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Fri May 16 16:39:57 CEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.protodata:protodata-cli:0.95.0`
+# Dependencies of `io.spine.protodata:protodata-cli:0.95.1`
 
 ## Runtime
 1.  **Group** : com.fasterxml.jackson. **Name** : jackson-bom. **Version** : 2.18.3.
@@ -4225,12 +4225,12 @@ This report was generated on **Thu May 08 19:15:03 WEST 2025** using [Gradle-Lic
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Thu May 08 19:15:03 WEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Fri May 16 16:39:58 CEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.protodata:protodata-gradle-api:0.95.0`
+# Dependencies of `io.spine.protodata:protodata-gradle-api:0.95.1`
 
 ## Runtime
 1.  **Group** : com.fasterxml.jackson. **Name** : jackson-bom. **Version** : 2.18.3.
@@ -5275,12 +5275,12 @@ This report was generated on **Thu May 08 19:15:03 WEST 2025** using [Gradle-Lic
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Thu May 08 19:15:03 WEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Fri May 16 16:39:59 CEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.protodata:protodata-gradle-plugin:0.95.0`
+# Dependencies of `io.spine.protodata:protodata-gradle-plugin:0.95.1`
 
 ## Runtime
 1.  **Group** : com.fasterxml.jackson. **Name** : jackson-bom. **Version** : 2.18.3.
@@ -6381,12 +6381,12 @@ This report was generated on **Thu May 08 19:15:03 WEST 2025** using [Gradle-Lic
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Thu May 08 19:15:04 WEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Fri May 16 16:39:59 CEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.protodata:protodata-java:0.95.0`
+# Dependencies of `io.spine.protodata:protodata-java:0.95.1`
 
 ## Runtime
 1.  **Group** : com.fasterxml.jackson. **Name** : jackson-bom. **Version** : 2.18.3.
@@ -7496,12 +7496,12 @@ This report was generated on **Thu May 08 19:15:04 WEST 2025** using [Gradle-Lic
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Thu May 08 19:15:04 WEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Fri May 16 16:40:00 CEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.protodata:protodata-params:0.95.0`
+# Dependencies of `io.spine.protodata:protodata-params:0.95.1`
 
 ## Runtime
 1.  **Group** : com.fasterxml.jackson. **Name** : jackson-bom. **Version** : 2.18.3.
@@ -8618,12 +8618,12 @@ This report was generated on **Thu May 08 19:15:04 WEST 2025** using [Gradle-Lic
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Thu May 08 19:15:04 WEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Fri May 16 16:40:00 CEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.protodata:protodata-protoc:0.95.0`
+# Dependencies of `io.spine.protodata:protodata-protoc:0.95.1`
 
 ## Runtime
 1.  **Group** : com.google.code.findbugs. **Name** : jsr305. **Version** : 3.0.2.
@@ -9410,12 +9410,12 @@ This report was generated on **Thu May 08 19:15:04 WEST 2025** using [Gradle-Lic
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Thu May 08 19:15:04 WEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Fri May 16 16:40:00 CEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.protodata:protodata-test-env:0.95.0`
+# Dependencies of `io.spine.protodata:protodata-test-env:0.95.1`
 
 ## Runtime
 1.  **Group** : com.fasterxml.jackson. **Name** : jackson-bom. **Version** : 2.18.3.
@@ -10536,12 +10536,12 @@ This report was generated on **Thu May 08 19:15:04 WEST 2025** using [Gradle-Lic
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Thu May 08 19:15:05 WEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Fri May 16 16:40:00 CEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.protodata:protodata-testlib:0.95.0`
+# Dependencies of `io.spine.protodata:protodata-testlib:0.95.1`
 
 ## Runtime
 1.  **Group** : com.fasterxml.jackson. **Name** : jackson-bom. **Version** : 2.18.3.
@@ -11749,4 +11749,4 @@ This report was generated on **Thu May 08 19:15:05 WEST 2025** using [Gradle-Lic
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Thu May 08 19:15:05 WEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
+This report was generated on **Fri May 16 16:40:01 CEST 2025** using [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).

java/src/main/kotlin/io/spine/protodata/java/StringExpressions.kt

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2025, TeamDev. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Redistribution and use in source and/or binary forms, with or without
+ * modification, must retain the above copyright notice and the following
+ * disclaimer.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package io.spine.protodata.java
+
+/**
+ * Yields a new string [Expression] by concatenating this [Expression]
+ * with another [Expression].
+ */
+public operator fun Expression<String>.plus(value: Expression<String>): Expression<String> =
+    Expression("$this + $value")
+
+/**
+ * Yields a new string [Expression] by appending the given [String]
+ * literal to this string [Expression].
+ */
+public operator fun Expression<String>.plus(value: String): Expression<String> =
+    plus(StringLiteral(value))