Add auto-config for ComponentFlow

- ComponentFlowAutoConfiguration which creates a builder bean
  and configures ComponentFlowCustomizer to set needed
  defaults for terminal, resource loader and template executor.
- Fixes #387

spring-shell-autoconfigure/src/main/java/org/springframework/shell/boot/ComponentFlowAutoConfiguration.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * 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
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.shell.boot;
+
+import org.jline.terminal.Terminal;
+
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Scope;
+import org.springframework.core.annotation.Order;
+import org.springframework.core.io.ResourceLoader;
+import org.springframework.shell.component.flow.ComponentFlow;
+import org.springframework.shell.component.flow.ComponentFlow.Builder;
+import org.springframework.shell.style.TemplateExecutor;
+
+/**
+ * {@link EnableAutoConfiguration Auto-configuration} for {@link ComponentFlow}.
+ *
+ * @author Janne Valkealahti
+ */
+@Configuration(proxyBeanMethods = false)
+@ConditionalOnClass(ComponentFlow.class)
+public class ComponentFlowAutoConfiguration {
+
+	@Bean
+	@Scope("prototype")
+	@ConditionalOnMissingBean
+	public ComponentFlow.Builder componentFlowBuilder(ObjectProvider<ComponentFlowCustomizer> customizerProvider) {
+		ComponentFlow.Builder builder = ComponentFlow.builder();
+		customizerProvider.orderedStream().forEach((customizer) -> customizer.customize(builder));
+		return builder;
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	protected static class ComponentFlowConfiguration {
+
+		@Bean
+		@ConditionalOnMissingBean
+		@Order(0)
+		public ComponentFlowCustomizer exchangeStrategiesCustomizer(ObjectProvider<Terminal> terminal,
+				ObjectProvider<ResourceLoader> resourceLoader, ObjectProvider<TemplateExecutor> templateExecutor) {
+			return new CommonComponentFlowCustomizer(terminal, resourceLoader, templateExecutor);
+		}
+
+	}
+
+	private static class CommonComponentFlowCustomizer implements ComponentFlowCustomizer {
+
+		private final ObjectProvider<Terminal> terminal;
+		private final ObjectProvider<ResourceLoader> resourceLoader;
+		private final ObjectProvider<TemplateExecutor> templateExecutor;
+
+		CommonComponentFlowCustomizer(ObjectProvider<Terminal> terminal, ObjectProvider<ResourceLoader> resourceLoader,
+				ObjectProvider<TemplateExecutor> templateExecutor) {
+			this.terminal = terminal;
+			this.resourceLoader = resourceLoader;
+			this.templateExecutor = templateExecutor;
+		}
+
+		@Override
+		public void customize(Builder componentFlowBuilder) {
+			terminal.ifAvailable(dep -> componentFlowBuilder.terminal(dep));
+			resourceLoader.ifAvailable(dep -> componentFlowBuilder.resourceLoader(dep));
+			templateExecutor.ifAvailable(dep -> componentFlowBuilder.templateExecutor(dep));
+		}
+	}
+}

spring-shell-autoconfigure/src/main/java/org/springframework/shell/boot/ComponentFlowCustomizer.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * 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
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.shell.boot;
+
+import org.springframework.shell.component.flow.ComponentFlow;
+
+/**
+ * Callback interface that can be used to customize a {@link ComponentFlow.Builder}.
+ *
+ * @author Janne Valkealahti
+ */
+@FunctionalInterface
+public interface ComponentFlowCustomizer {
+
+	/**
+	 * Callback to customize a {@link ComponentFlow.Builder} instance.
+	 * @param componentFlowBuilder the component flow builder to customize
+	 */
+	void customize(ComponentFlow.Builder componentFlowBuilder);
+}

spring-shell-autoconfigure/src/main/resources/META-INF/spring.factories

@@ -12,4 +12,5 @@ org.springframework.shell.boot.JCommanderParameterResolverAutoConfiguration,\
 org.springframework.shell.boot.ParameterResolverAutoConfiguration,\
 org.springframework.shell.boot.StandardAPIAutoConfiguration,\
 org.springframework.shell.boot.ThemingAutoConfiguration,\
-org.springframework.shell.boot.StandardCommandsAutoConfiguration
+org.springframework.shell.boot.StandardCommandsAutoConfiguration,\
+org.springframework.shell.boot.ComponentFlowAutoConfiguration