Completion command for bash

- Add basic support of defining a command `completion bash` which
  outputs a generic bash script which can be used in a user environment.
- Idea for completion is copied from go's cobra library what comes for
  a bash dance itself.
- Goes through command registry, builds a model for command structure
  and uses antlr st4 for templating bash.
- Should give foundation to create other completions just like in cobra.
- Currently as we don't know a root-command in a generic way, option
  `spring.shell.command.completion.root-command` is required user to set.
- Fixes #343

spring-shell-standard/src/test/java/org/springframework/shell/standard/completion/AbstractCompletionsTests.java

@@ -0,0 +1,140 @@
+/*
+ * 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.standard.completion;
+
+import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.core.convert.support.DefaultConversionService;
+import org.springframework.core.io.DefaultResourceLoader;
+import org.springframework.core.io.ResourceLoader;
+import org.springframework.shell.CommandRegistry;
+import org.springframework.shell.ConfigurableCommandRegistry;
+import org.springframework.shell.MethodTarget;
+import org.springframework.shell.ParameterResolver;
+import org.springframework.shell.standard.ShellMethod;
+import org.springframework.shell.standard.ShellOption;
+import org.springframework.shell.standard.StandardParameterResolver;
+import org.springframework.shell.standard.completion.AbstractCompletions.CommandModel;
+import org.springframework.util.ReflectionUtils;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class AbstractCompletionsTests {
+
+	@Test
+	public void testBasicModelGeneration() {
+		DefaultResourceLoader resourceLoader = new DefaultResourceLoader();
+		ConfigurableCommandRegistry commandRegistry = new ConfigurableCommandRegistry();
+		List<ParameterResolver> parameterResolvers = new ArrayList<>();
+		StandardParameterResolver resolver = new StandardParameterResolver(new DefaultConversionService(),
+				Collections.emptySet());
+		parameterResolvers.add(resolver);
+
+		TestCommands commands = new TestCommands();
+
+		Method method1 = ReflectionUtils.findMethod(TestCommands.class, "test1", String.class);
+		Method method2 = ReflectionUtils.findMethod(TestCommands.class, "test2");
+		Method method3 = ReflectionUtils.findMethod(TestCommands.class, "test3");
+		Method method4 = ReflectionUtils.findMethod(TestCommands.class, "test4", String.class);
+
+		MethodTarget methodTarget1 = new MethodTarget(method1, commands, "help");
+		MethodTarget methodTarget2 = new MethodTarget(method2, commands, "help");
+		MethodTarget methodTarget3 = new MethodTarget(method3, commands, "help");
+		MethodTarget methodTarget4 = new MethodTarget(method4, commands, "help");
+
+		commandRegistry.register("test1", methodTarget1);
+		commandRegistry.register("test2", methodTarget2);
+		commandRegistry.register("test3", methodTarget3);
+		commandRegistry.register("test3 test4", methodTarget4);
+
+		TestCompletions completions = new TestCompletions(resourceLoader, commandRegistry, parameterResolvers);
+		CommandModel commandModel = completions.testCommandModel();
+		assertThat(commandModel.getCommands()).hasSize(3);
+		assertThat(commandModel.getCommands().stream().map(c -> c.getMainCommand())).containsExactlyInAnyOrder("test1", "test2",
+				"test3");
+		assertThat(commandModel.getCommands().stream().filter(c -> c.getMainCommand().equals("test1")).findFirst().get()
+				.getOptions()).hasSize(1);
+		assertThat(commandModel.getCommands().stream().filter(c -> c.getMainCommand().equals("test1")).findFirst().get()
+				.getOptions().get(0).option()).isEqualTo("--param1");
+		assertThat(commandModel.getCommands().stream().filter(c -> c.getMainCommand().equals("test2")).findFirst().get()
+				.getOptions()).hasSize(0);
+		assertThat(commandModel.getCommands().stream().filter(c -> c.getMainCommand().equals("test3")).findFirst().get()
+				.getOptions()).hasSize(0);
+		assertThat(commandModel.getCommands().stream().filter(c -> c.getMainCommand().equals("test3")).findFirst().get()
+				.getCommands()).hasSize(1);
+		assertThat(commandModel.getCommands().stream().filter(c -> c.getMainCommand().equals("test3")).findFirst().get()
+				.getCommands().get(0).getMainCommand()).isEqualTo("test4");
+		assertThat(commandModel.getCommands().stream().filter(c -> c.getMainCommand().equals("test3")).findFirst().get()
+				.getCommands().get(0).getOptions()).hasSize(1);
+		assertThat(commandModel.getCommands().stream().filter(c -> c.getMainCommand().equals("test3")).findFirst().get()
+				.getCommands().get(0).getOptions().get(0).option()).isEqualTo("--param4");
+	}
+
+	@Test
+	public void testBuilder() {
+		DefaultResourceLoader resourceLoader = new DefaultResourceLoader();
+		ConfigurableCommandRegistry commandRegistry = new ConfigurableCommandRegistry();
+		List<ParameterResolver> parameterResolvers = new ArrayList<>();
+		TestCompletions completions = new TestCompletions(resourceLoader, commandRegistry, parameterResolvers);
+
+		String result = completions.testBuilder()
+				.attribute("x", "command")
+				.group("classpath:completion/test.stg")
+				.appendGroup("a")
+				.build();
+		assertThat(result).contains("foocommand");
+	}
+
+	private static class TestCompletions extends AbstractCompletions {
+
+		public TestCompletions(ResourceLoader resourceLoader, CommandRegistry commandRegistry,
+				List<ParameterResolver> parameterResolvers) {
+			super(resourceLoader, commandRegistry, parameterResolvers);
+		}
+
+		CommandModel testCommandModel() {
+			return generateCommandModel();
+		}
+
+		Builder testBuilder() {
+			return super.builder();
+		}
+	}
+
+	private static class TestCommands {
+
+		@ShellMethod
+		void test1(@ShellOption String param1) {
+		}
+
+		@ShellMethod
+		void test2() {
+		}
+
+		@ShellMethod
+		void test3() {
+		}
+
+		@ShellMethod
+		void test4(@ShellOption String param4) {
+		}
+	}
+}

spring-shell-standard/src/test/java/org/springframework/shell/standard/completion/BashCompletionsTests.java

@@ -0,0 +1,57 @@
+/*
+ * 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.standard.completion;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.shell.ConfigurableCommandRegistry;
+import org.springframework.shell.ParameterResolver;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class BashCompletionsTests {
+
+	AnnotationConfigApplicationContext context;
+
+	@BeforeEach
+	public void setup() {
+		context = new AnnotationConfigApplicationContext();
+		context.refresh();
+	}
+
+	@AfterEach
+	public void clean() {
+		if (context != null) {
+			context.close();
+		}
+		context = null;
+	}
+
+	@Test
+	public void testDoesNotError() {
+		ConfigurableCommandRegistry commandRegistry = new ConfigurableCommandRegistry();
+		List<ParameterResolver> parameterResolvers = new ArrayList<>();
+		BashCompletions completions = new BashCompletions(context, commandRegistry, parameterResolvers);
+		String bash = completions.generate("root-command");
+		assertThat(bash).contains("root-command");
+	}
+}

spring-shell-standard/src/test/resources/completion/test.stg

@@ -0,0 +1,4 @@
+b(y) ::= "<y>"
+a(x) ::= <<
+foo<b(x)>
+>>