Add core JavaPoet utilities

This commit adds utilities that facilitate code generation patterns
used by the AOT engine.

Closes gh-28028

Author: snicoll

spring-core/src/main/java/org/springframework/javapoet/support/CodeSnippet.java

@@ -0,0 +1,188 @@
+/*
+ * Copyright 2002-2022 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.javapoet.support;
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.util.function.Consumer;
+import java.util.stream.Collectors;
+
+import javax.lang.model.element.Modifier;
+
+import org.springframework.javapoet.CodeBlock;
+import org.springframework.javapoet.JavaFile;
+import org.springframework.javapoet.MethodSpec;
+import org.springframework.javapoet.TypeSpec;
+
+/**
+ * A code snippet using tabs indentation that is fully processed by JavaPoet so
+ * that imports are resolved.
+ *
+ * @author Stephane Nicoll
+ * @since 6.0
+ */
+public final class CodeSnippet {
+
+	private static final String START_SNIPPET = "// start-snippet\n";
+
+	private static final String END_SNIPPET = "// end-snippet";
+
+	private final String fileContent;
+
+	private final String snippet;
+
+
+	CodeSnippet(String fileContent, String snippet) {
+		this.fileContent = fileContent;
+		this.snippet = snippet;
+	}
+
+
+	String getFileContent() {
+		return this.fileContent;
+	}
+
+	/**
+	 * Return the rendered code snippet.
+	 * @return a code snippet where imports have been resolved
+	 */
+	public String getSnippet() {
+		return this.snippet;
+	}
+
+	/**
+	 * Specify if an import statement for the specified type is present.
+	 * @param type the type to check
+	 * @return true if this type has an import statement, false otherwise
+	 */
+	public boolean hasImport(Class<?> type) {
+		return hasImport(type.getName());
+	}
+
+	/**
+	 * Specify if an import statement for the specified class name is present.
+	 * @param className the name of the class to check
+	 * @return true if this type has an import statement, false otherwise
+	 */
+	public boolean hasImport(String className) {
+		return getFileContent().lines().anyMatch(candidate ->
+				candidate.equals(String.format("import %s;", className)));
+	}
+
+	/**
+	 * Return a new {@link CodeSnippet} where the specified number of indentations
+	 * have been removed.
+	 * @param indent the number of indent to remove
+	 * @return a CodeSnippet instance with the number of indentations removed
+	 */
+	public CodeSnippet removeIndent(int indent) {
+		return new CodeSnippet(this.fileContent, this.snippet.lines().map(line ->
+				removeIndent(line, indent)).collect(Collectors.joining("\n")));
+	}
+
+	/**
+	 * Create a {@link CodeSnippet} using the specified code.
+	 * @param code the code snippet
+	 * @return a {@link CodeSnippet} instance
+	 */
+	public static CodeSnippet of(CodeBlock code) {
+		return new Builder().build(code);
+	}
+
+	/**
+	 * Process the specified code and return a fully-processed code snippet
+	 * as a String.
+	 * @param code a consumer to use to generate the code snippet
+	 * @return a resolved code snippet
+	 */
+	public static String process(Consumer<CodeBlock.Builder> code) {
+		CodeBlock.Builder body = CodeBlock.builder();
+		code.accept(body);
+		return process(body.build());
+	}
+
+	/**
+	 * Process the specified {@link CodeBlock code} and return a
+	 * fully-processed code snippet as a String.
+	 * @param code the code snippet
+	 * @return a resolved code snippet
+	 */
+	public static String process(CodeBlock code) {
+		return of(code).getSnippet();
+	}
+
+	private String removeIndent(String line, int indent) {
+		for (int i = 0; i < indent; i++) {
+			if (line.startsWith("\t")) {
+				line = line.substring(1);
+			}
+		}
+		return line;
+	}
+
+	private static final class Builder {
+
+		private static final String INDENT = "\t";
+
+		private static final String SNIPPET_INDENT = INDENT + INDENT;
+
+		public CodeSnippet build(CodeBlock code) {
+			MethodSpec.Builder method = MethodSpec.methodBuilder("test")
+					.addModifiers(Modifier.PUBLIC);
+			CodeBlock.Builder body = CodeBlock.builder();
+			body.add(START_SNIPPET);
+			body.add(code);
+			body.add(END_SNIPPET);
+			method.addCode(body.build());
+			String fileContent = write(createTestJavaFile(method.build()));
+			String snippet = isolateGeneratedContent(fileContent);
+			return new CodeSnippet(fileContent, snippet);
+		}
+
+		private String isolateGeneratedContent(String javaFile) {
+			int start = javaFile.indexOf(START_SNIPPET);
+			String tmp = javaFile.substring(start + START_SNIPPET.length());
+			int end = tmp.indexOf(END_SNIPPET);
+			tmp = tmp.substring(0, end);
+			// Remove indent
+			return tmp.lines().map(line -> {
+				if (!line.startsWith(SNIPPET_INDENT)) {
+					throw new IllegalStateException("Missing indent for " + line);
+				}
+				return line.substring(SNIPPET_INDENT.length());
+			}).collect(Collectors.joining("\n"));
+		}
+
+		private JavaFile createTestJavaFile(MethodSpec method) {
+			return JavaFile.builder("example", TypeSpec.classBuilder("Test")
+					.addModifiers(Modifier.PUBLIC)
+					.addMethod(method).build()).indent(INDENT).build();
+		}
+
+		private String write(JavaFile file) {
+			try {
+				StringWriter out = new StringWriter();
+				file.writeTo(out);
+				return out.toString();
+			}
+			catch (IOException ex) {
+				throw new IllegalStateException("Failed to write " + file, ex);
+			}
+		}
+
+	}
+}

spring-core/src/main/java/org/springframework/javapoet/support/MultiCodeBlock.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2002-2022 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.javapoet.support;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Consumer;
+
+import org.springframework.javapoet.CodeBlock;
+import org.springframework.javapoet.CodeBlock.Builder;
+
+
+/**
+ * A {@link CodeBlock} wrapper for joining multiple blocks.
+ *
+ * @author Stephane Nicoll
+ * @since 6.0
+ */
+public class MultiCodeBlock {
+
+	private final List<CodeBlock> codeBlocks = new ArrayList<>();
+
+
+	/**
+	 * Add the specified {@link CodeBlock}.
+	 * @param code the code block to add
+	 */
+	public void add(CodeBlock code) {
+		if (code.isEmpty()) {
+			throw new IllegalArgumentException("Could not add empty CodeBlock");
+		}
+		this.codeBlocks.add(code);
+	}
+
+	/**
+	 * Add a {@link CodeBlock} using the specified callback.
+	 * @param code the callback to use
+	 */
+	public void add(Consumer<Builder> code) {
+		Builder builder = CodeBlock.builder();
+		code.accept(builder);
+		add(builder.build());
+	}
+
+	/**
+	 * Add a code block using the specified formatted String and the specified
+	 * arguments.
+	 * @param code the code
+	 * @param arguments the arguments
+	 * @see Builder#add(String, Object...)
+	 */
+	public void add(String code, Object... arguments) {
+		add(CodeBlock.of(code, arguments));
+	}
+
+	/**
+	 * Return a {@link CodeBlock} that joins the different blocks registered in
+	 * this instance with the specified delimiter.
+	 * @param delimiter the delimiter to use (not {@literal null})
+	 * @return a {@link CodeBlock} joining the blocks of this instance with the
+	 * specified {@code delimiter}
+	 * @see CodeBlock#join(Iterable, String)
+	 */
+	public CodeBlock join(String delimiter) {
+		return CodeBlock.join(this.codeBlocks, delimiter);
+	}
+
+}