Don't erase configuration file on YAML-dump failure

configlib-yaml/src/main/java/de/exlll/configlib/YamlConfigurationStore.java

@@ -73,8 +73,8 @@ public void write(T configuration, OutputStream outputStream) {
         requireNonNull(configuration, "configuration");
         requireNonNull(outputStream, "output stream");
         var extractedCommentNodes = extractor.extractCommentNodes(configuration);
-        var yamlFileWriter = new YamlWriter(outputStream, properties);
         var dumpedYaml = tryDump(configuration);
+        var yamlFileWriter = new YamlWriter(outputStream, properties);
         yamlFileWriter.writeYaml(dumpedYaml, extractedCommentNodes);
     }
 
@@ -84,8 +84,8 @@ public void save(T configuration, Path configurationFile) {
         requireNonNull(configurationFile, "configuration file");
         tryCreateParentDirectories(configurationFile);
         var extractedCommentNodes = extractor.extractCommentNodes(configuration);
-        var yamlFileWriter = new YamlWriter(configurationFile, properties);
         var dumpedYaml = tryDump(configuration);
+        var yamlFileWriter = new YamlWriter(configurationFile, properties);
         yamlFileWriter.writeYaml(dumpedYaml, extractedCommentNodes);
     }
 

configlib-yaml/src/test/java/de/exlll/configlib/YamlConfigurationStoreTest.java

@@ -572,4 +572,65 @@ void tryCreateParentDirectoriesDoesNotThrowIfParentIsNull(boolean createParentDi
         Path path = fs.getPath("config.yml");
         assertDoesNotThrow(() -> store.tryCreateParentDirectories(path));
     }
+
+    private record ThrowingWhileSerializingSerializer()
+            implements Serializer<String, String> {
+
+        @Override
+        public String serialize(String element) {
+            throw new UnsupportedOperationException(element);
+        }
+
+        @Override
+        public String deserialize(String element) {
+            return element;
+        }
+    }
+
+    @Configuration
+    private static final class G {
+        private String content = "-";
+    }
+
+    @Test
+    void saveDoesNotOverwriteConfigurationFileContentsOnYamlDumpFailure() throws IOException {
+        YamlConfigurationStore<G> store = new YamlConfigurationStore<>(
+                G.class,
+                YamlConfigurationProperties.newBuilder()
+                        .addSerializer(String.class, new ThrowingWhileSerializingSerializer())
+                        .build()
+        );
+
+        String content = "content: abcde";
+        Files.writeString(yamlFile, content);
+
+        G config = store.load(yamlFile);
+        assertThat(config.content, is("abcde"));
+        assertThrows(
+                UnsupportedOperationException.class,
+                () -> store.save(config, yamlFile)
+        );
+        assertThat(readFile(yamlFile), is(content));
+    }
+
+    @Test
+    void writeDoesNotOverwriteStreamContentsOnYamlDumpFailure() {
+        YamlConfigurationStore<G> store = new YamlConfigurationStore<>(
+                G.class,
+                YamlConfigurationProperties.newBuilder()
+                        .addSerializer(String.class, new ThrowingWhileSerializingSerializer())
+                        .build()
+        );
+
+        String content = "content: abcde";
+        outputStream.writeBytes(content.getBytes());
+
+        G config = store.read(inputFromOutput());
+        assertThat(config.content, is("abcde"));
+        assertThrows(
+                UnsupportedOperationException.class,
+                () -> store.write(config, outputStream)
+        );
+        assertThat(outputStream.toString(), is(content));
+    }
 }