Type-safe messages - support logical lines in localized files

docs/src/main/asciidoc/qute-reference.adoc

@@ -1713,22 +1713,36 @@ public interface GermanAppMessages extends AppMessages {
 Message bundle files must be encoded in UTF-8.
 The file name consists of the relevant bundle name (e.g. `msg`) and underscore followed by the locate tag (IETF).
 The file format is very simple: each line represents either a key/value pair with the equals sign used as a separator or a comment (line starts with `#`).
-Keys are mapped to method names from the corresponding message bundle interface.
+Blank lines are ignored.
+Keys are _mapped to method names_ from the corresponding message bundle interface.
 Values represent the templates normally defined by `io.quarkus.qute.i18n.Message#value()`.
-We use `.properties` suffix in our example because most IDEs and text editors support syntax highlighting of `.properties` files.
-But in fact, the suffix could be anything.
+A value may be spread out across several adjacent normal lines.
+In such case, the line terminator must be escaped with a backslash character `\`.
+The behavior is very similar to the behavior of the `java.util.Properties.load(Reader)` method.
 
 .Localized File Example - `msg_de.properties`
 [source,properties]
 ----
+# This comment is ignored
 hello_name=Hallo {name}! <1> <2>
 ----
 <1> Each line in a localized file represents a key/value pair. The key must correspond to a method declared on the message bundle interface. The value is the message template.
 <2> Keys and values are separated by the equals sign.
 
+NOTE: We use the `.properties` suffix in our example because most IDEs and text editors support syntax highlighting of `.properties` files. But in fact, the suffix could be anything - it is just ignored.
+
 TIP: An example properties file is generated into the target directory for each message bundle interface automatically. For example, by default if no name is specified for `@MessageBundle` the file `target/qute-i18n-examples/msg.properties` is generated when the application is build via `mvn clean package`. You can use this file as a base for a specific locale. Just rename the file - e.g. `msg_fr.properties`, change the message templates and move it in the `src/main/resources/messages` directory.
 
-Once we have the localized bundles defined we need a way to _select_ a correct bundle.
+.Value Spread Out Across Several Adjacent Lines
+[source,properties]
+----
+hello=Hello \
+   {name} and \
+   good morning!
+----
+Note that the line terminator is escaped with a backslash character `\` and white space at the start of the following line is ignored. I.e. `{msg:hello('Edgar')}` would be rendered as `Hello Edgar and good morning!`.
+
+Once we have the localized bundles defined we need a way to _select_ the correct bundle.
 If you use a message bundle expression in a template you'll have to specify the `locale` attribute of a template instance.
 
 .`locale` Attribute Example

extensions/qute/deployment/src/main/java/io/quarkus/qute/deployment/MessageBundleProcessor.java

@@ -15,6 +15,7 @@
 import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.ListIterator;
 import java.util.Locale;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -546,25 +547,34 @@ private Map<String, String> generateImplementations(List<MessageBundleBuildItem>
             for (Entry<String, Path> entry : bundle.getLocalizedFiles().entrySet()) {
                 Path localizedFile = entry.getValue();
                 Map<String, String> keyToTemplate = new HashMap<>();
-                int linesProcessed = 0;
-                for (String line : Files.readAllLines(localizedFile)) {
-                    linesProcessed++;
-                    if (!line.startsWith("#")) {
-                        int eqIndex = line.indexOf('=');
-                        if (eqIndex == -1) {
-                            throw new MessageBundleException(
-                                    "Missing key/value separator\n\t- file: " + localizedFile + "\n\t- line " + linesProcessed);
-                        }
-                        String key = line.substring(0, eqIndex).trim();
-                        if (!hasMessageBundleMethod(bundleInterface, key)) {
-                            throw new MessageBundleException(
-                                    "Message bundle method " + key + "() not found on: " + bundleInterface + "\n\t- file: "
-                                            + localizedFile + "\n\t- line " + linesProcessed);
-                        }
-                        String value = line.substring(eqIndex + 1, line.length()).trim();
+                for (ListIterator<String> it = Files.readAllLines(localizedFile).listIterator(); it.hasNext();) {
+                    String line = it.next();
+                    if (line.startsWith("#") || line.isBlank()) {
+                        // Comments and blank lines are skipped
+                        continue;
+                    }
+                    int eqIdx = line.indexOf('=');
+                    if (eqIdx == -1) {
+                        throw new MessageBundleException(
+                                "Missing key/value separator\n\t- file: " + localizedFile + "\n\t- line " + it.previousIndex());
+                    }
+                    String key = line.substring(0, eqIdx).strip();
+                    if (!hasMessageBundleMethod(bundleInterface, key)) {
+                        throw new MessageBundleException(
+                                "Message bundle method " + key + "() not found on: " + bundleInterface + "\n\t- file: "
+                                        + localizedFile + "\n\t- line " + it.previousIndex());
+                    }
+                    String value = adaptLine(line.substring(eqIdx + 1, line.length()));
+                    if (value.endsWith("\\")) {
+                        // The logical line is spread out across several normal lines
+                        StringBuilder builder = new StringBuilder(value.substring(0, value.length() - 1));
+                        constructLine(builder, it);
+                        keyToTemplate.put(key, builder.toString());
+                    } else {
                         keyToTemplate.put(key, value);
                     }
                 }
+
                 String locale = entry.getKey();
                 ClassOutput localeAwareGizmoAdaptor = new GeneratedClassGizmoAdaptor(generatedClasses,
                         new AppClassPredicate(applicationArchivesBuildItem,
@@ -587,6 +597,22 @@ public String apply(String className) {
         return generatedTypes;
     }
 
+    private void constructLine(StringBuilder builder, Iterator<String> it) {
+        if (it.hasNext()) {
+            String nextLine = adaptLine(it.next());
+            if (nextLine.endsWith("\\")) {
+                builder.append(nextLine.substring(0, nextLine.length() - 1));
+                constructLine(builder, it);
+            } else {
+                builder.append(nextLine);
+            }
+        }
+    }
+
+    private String adaptLine(String line) {
+        return line.stripLeading().replace("\\n", "\n");
+    }
+
     private boolean hasMessageBundleMethod(ClassInfo bundleInterface, String name) {
         for (MethodInfo method : bundleInterface.methods()) {
             if (method.name().equals(name) && method.hasAnnotation(Names.MESSAGE)) {

extensions/qute/deployment/src/test/java/io/quarkus/qute/deployment/i18n/MessageBundleLogicalLineTest.java

@@ -0,0 +1,56 @@
+package io.quarkus.qute.deployment.i18n;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Locale;
+
+import javax.inject.Inject;
+
+import org.jboss.shrinkwrap.api.ShrinkWrap;
+import org.jboss.shrinkwrap.api.asset.StringAsset;
+import org.jboss.shrinkwrap.api.spec.JavaArchive;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import io.quarkus.qute.Template;
+import io.quarkus.qute.i18n.Message;
+import io.quarkus.qute.i18n.MessageBundle;
+import io.quarkus.qute.i18n.MessageBundles;
+import io.quarkus.test.QuarkusUnitTest;
+
+public class MessageBundleLogicalLineTest {
+
+    @RegisterExtension
+    static final QuarkusUnitTest config = new QuarkusUnitTest()
+            .setArchiveProducer(() -> ShrinkWrap.create(JavaArchive.class)
+                    .addClasses(Messages.class)
+                    .addAsResource("messages/msg_cs.properties")
+                    .addAsResource(new StringAsset(
+                            "{msg:hello('Edgar')} {msg:helloNextLine('Edgar')} ::{msg:fruits}"),
+                            "templates/foo.html"));
+
+    @Inject
+    Template foo;
+
+    @Test
+    public void testResolvers() {
+        assertEquals("Hello Edgar! Hello \n Edgar! ::apple, banana, pear, watermelon, kiwi, mango",
+                foo.render());
+        assertEquals("Ahoj Edgar a dobrý den! Ahoj \n Edgar! ::apple, banana, pear, watermelon, kiwi, mango",
+                foo.instance().setAttribute(MessageBundles.ATTRIBUTE_LOCALE, Locale.forLanguageTag("cs")).render());
+    }
+
+    @MessageBundle(locale = "en")
+    public interface Messages {
+
+        @Message("Hello {name}!")
+        String hello(String name);
+
+        @Message("Hello \n {name}!")
+        String helloNextLine(String name);
+
+        @Message("apple, banana, pear, watermelon, kiwi, mango")
+        String fruits();
+    }
+
+}

extensions/qute/deployment/src/test/resources/messages/msg_cs.properties

@@ -0,0 +1,9 @@
+hello=Ahoj \
+   {name} a \
+   dobrý den!
+
+helloNextLine=Ahoj \n {name}!
+ fruits =        apple, banana, pear, \
+                  watermelon, \
+                 kiwi, mango
+