From 6d4255ff94281583bb69b0a4096b2b78313d39da Mon Sep 17 00:00:00 2001
From: Michael Keppler <Michael.Keppler@gmx.de>
Date: Thu, 16 Nov 2023 21:03:37 +0100
Subject: [PATCH] Avoid calling parsers when there are no source files

With empty lists of main or test, Java or Kotlin files avoid invoking
the parsers completely. That's more performant and avoids any bad side
effects during initialization of the parsers.

Fixes #658.
---
 .../maven/MavenMojoProjectParser.java         | 24 +++++++++----------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/src/main/java/org/openrewrite/maven/MavenMojoProjectParser.java b/src/main/java/org/openrewrite/maven/MavenMojoProjectParser.java
index c0ba74af..bbfb5355 100644
--- a/src/main/java/org/openrewrite/maven/MavenMojoProjectParser.java
+++ b/src/main/java/org/openrewrite/maven/MavenMojoProjectParser.java
@@ -323,13 +323,13 @@ private Stream<SourceFile> processMainSources(
         javaParserBuilder.classpath(dependencies).typeCache(typeCache);
         kotlinParserBuilder.classpath(dependencies).typeCache(new JavaTypeCache());
 
-        Stream<? extends SourceFile> cus = Stream.of(javaParserBuilder)
-                .map(JavaParser.Builder::build)
-                .flatMap(parser -> parser.parse(mainJavaSources, baseDir, ctx));
+        Stream<? extends SourceFile> cus = mainJavaSources.isEmpty() ? Stream.empty()
+                : Stream.of(javaParserBuilder).map(JavaParser.Builder::build)
+                        .flatMap(parser -> parser.parse(mainJavaSources, baseDir, ctx));
 
-        Stream<? extends SourceFile> kcus = Stream.of(kotlinParserBuilder)
-                .map(KotlinParser.Builder::build)
-                .flatMap(parser -> parser.parse(mainKotlinSources, baseDir, ctx));
+        Stream<? extends SourceFile> kcus = mainKotlinSources.isEmpty() ? Stream.empty()
+                : Stream.of(kotlinParserBuilder).map(KotlinParser.Builder::build)
+                        .flatMap(parser -> parser.parse(mainKotlinSources, baseDir, ctx));
 
         List<Marker> mainProjectProvenance = new ArrayList<>(projectProvenance);
         mainProjectProvenance.add(sourceSet("main", dependencies, typeCache));
@@ -382,13 +382,13 @@ private Stream<SourceFile> processTestSources(
 
         alreadyParsed.addAll(testKotlinSources);
 
-        Stream<? extends SourceFile> cus = Stream.of(javaParserBuilder)
-                .map(JavaParser.Builder::build)
-                .flatMap(parser -> parser.parse(testJavaSources, baseDir, ctx));
+        Stream<? extends SourceFile> cus = testJavaSources.isEmpty() ? Stream.empty()
+                : Stream.of(javaParserBuilder).map(JavaParser.Builder::build)
+                        .flatMap(parser -> parser.parse(testJavaSources, baseDir, ctx));
 
-        Stream<? extends SourceFile> kcus = Stream.of(kotlinParserBuilder)
-                .map(KotlinParser.Builder::build)
-                .flatMap(parser -> parser.parse(testKotlinSources, baseDir, ctx));
+        Stream<? extends SourceFile> kcus = testKotlinSources.isEmpty() ? Stream.empty()
+                : Stream.of(kotlinParserBuilder).map(KotlinParser.Builder::build)
+                        .flatMap(parser -> parser.parse(testKotlinSources, baseDir, ctx));
 
         List<Marker> markers = new ArrayList<>(projectProvenance);
         markers.add(sourceSet("test", testDependencies, typeCache));