Move comments along with their dependency when sorting Gradle dependencies (#7517)

The Gradle parser stores line-comments preceding a statement on that statement's prefix.
The previous implementation overwrote each sorted statement's prefix with the prefix at
its new position, causing comments to remain in place while dependencies moved around them.
Now each statement keeps its own prefix, and only the leading whitespace of the new first
statement is harmonized to preserve block-opening formatting.

Fixes #7516

Author: timtebeek

rewrite-gradle/src/main/java/org/openrewrite/gradle/SortDependencies.java

@@ -27,6 +27,7 @@
 import org.openrewrite.java.MethodMatcher;
 import org.openrewrite.java.tree.Expression;
 import org.openrewrite.java.tree.J;
+import org.openrewrite.java.tree.Space;
 import org.openrewrite.java.tree.Statement;
 import org.openrewrite.maven.tree.Dependency;
 import org.openrewrite.maven.tree.DependencyNotation;
@@ -78,7 +79,6 @@ public J.MethodInvocation visitMethodInvocation(J.MethodInvocation method, Execu
                     return m;
                 }
 
-                // Separate dependency statements from non-dependency statements (comments are whitespace in Gradle AST)
                 List<Statement> sorted = new ArrayList<>(statements);
                 sorted.sort(dependencyComparator);
 
@@ -95,9 +95,20 @@ public J.MethodInvocation visitMethodInvocation(J.MethodInvocation method, Execu
                     return m;
                 }
 
-                // Preserve original whitespace prefixes
-                for (int i = 0; i < sorted.size(); i++) {
-                    sorted.set(i, sorted.get(i).withPrefix(statements.get(i).getPrefix()));
+                // Keep each statement's prefix with the statement itself so that any preceding comments
+                // (which the parser stores on the next statement's prefix) move along with the dependency.
+                // Swap only the leading whitespace of the new first statement with the original first
+                // statement's leading whitespace, to keep the block opening formatting consistent.
+                Space originalFirstPrefix = statements.get(0).getPrefix();
+                Space newFirstPrefix = sorted.get(0).getPrefix();
+                sorted.set(0, sorted.get(0).withPrefix(newFirstPrefix.withWhitespace(originalFirstPrefix.getWhitespace())));
+                // Apply the displaced leading whitespace to whichever sorted statement now follows the
+                // original first statement, to preserve the block-internal blank-line layout.
+                int originalFirstIndex = sorted.indexOf(statements.get(0));
+                if (originalFirstIndex > 0) {
+                    Space displacedPrefix = sorted.get(originalFirstIndex).getPrefix();
+                    sorted.set(originalFirstIndex, sorted.get(originalFirstIndex)
+                      .withPrefix(displacedPrefix.withWhitespace(newFirstPrefix.getWhitespace())));
                 }
 
                 body = body.withStatements(sorted);

rewrite-gradle/src/test/java/org/openrewrite/gradle/SortDependenciesTest.java

@@ -220,4 +220,134 @@ void configurationGroupingTakesPrecedence() {
           )
         );
     }
+
+    @Test
+    void preservesCommentsAttachedToDependencies() {
+        rewriteRun(
+          buildGradle(
+            """
+              plugins {
+                  id 'java-library'
+              }
+
+              repositories {
+                  mavenCentral()
+              }
+
+              dependencies {
+                  // Spring web for the controllers
+                  implementation "org.springframework:spring-web:5.3.23"
+                  // Guava for collection helpers
+                  api "com.google.guava:guava:31.1-jre"
+              }
+              """,
+            """
+              plugins {
+                  id 'java-library'
+              }
+
+              repositories {
+                  mavenCentral()
+              }
+
+              dependencies {
+                  // Guava for collection helpers
+                  api "com.google.guava:guava:31.1-jre"
+                  // Spring web for the controllers
+                  implementation "org.springframework:spring-web:5.3.23"
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void preservesCommentsAttachedToDependenciesKotlinDsl() {
+        rewriteRun(
+          buildGradleKts(
+            """
+              plugins {
+                  `java-library`
+              }
+
+              repositories {
+                  mavenCentral()
+              }
+
+              dependencies {
+                  // Spring web for the controllers
+                  implementation("org.springframework:spring-web:5.3.23")
+
+                  // Guava for collection helpers
+                  api("com.google.guava:guava:31.1-jre")
+              }
+              """,
+            """
+              plugins {
+                  `java-library`
+              }
+
+              repositories {
+                  mavenCentral()
+              }
+
+              dependencies {
+                  // Guava for collection helpers
+                  api("com.google.guava:guava:31.1-jre")
+
+                  // Spring web for the controllers
+                  implementation("org.springframework:spring-web:5.3.23")
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void preservesCommentsBlocksWithBlankLines() {
+        rewriteRun(
+          buildGradle(
+            """
+              plugins {
+                  id 'java-library'
+              }
+
+              repositories {
+                  mavenCentral()
+              }
+
+              dependencies {
+                  // Enable the Swing console
+                  implementation "org.springframework:spring-web:5.3.23"
+
+                  // Enable Guava
+                  api "com.google.guava:guava:31.1-jre"
+
+                  // Enable JUnit
+                  testImplementation "org.junit.jupiter:junit-jupiter-api:5.9.1"
+              }
+              """,
+            """
+              plugins {
+                  id 'java-library'
+              }
+
+              repositories {
+                  mavenCentral()
+              }
+
+              dependencies {
+                  // Enable Guava
+                  api "com.google.guava:guava:31.1-jre"
+
+                  // Enable the Swing console
+                  implementation "org.springframework:spring-web:5.3.23"
+
+                  // Enable JUnit
+                  testImplementation "org.junit.jupiter:junit-jupiter-api:5.9.1"
+              }
+              """
+          )
+        );
+    }
 }