Adds Collapse Spec Optionss to Maven Plugin

* Adds a collapsedSpec option to the maven plugin that produces a single-file representation of the spec in the output directory.
* Adds a includeCollapsedSpecInArtifacts option to the maven plugin that adds the collapsed spec file to the maven artifacts.

modules/openapi-generator-maven-plugin/src/main/java/org/openapitools/codegen/plugin/CodeGenMojo.java

@@ -20,6 +20,10 @@
 import static org.apache.commons.lang3.StringUtils.isNotEmpty;
 import static org.openapitools.codegen.config.CodegenConfiguratorUtils.*;
 
+import io.swagger.v3.core.util.Json;
+import io.swagger.v3.core.util.Yaml;
+import io.swagger.v3.parser.OpenAPIResolver;
+import io.swagger.v3.parser.OpenAPIV3Parser;
 import io.swagger.v3.parser.core.models.AuthorizationValue;
 import java.io.File;
 import java.io.FileOutputStream;
@@ -33,13 +37,17 @@
 import java.nio.channels.FileChannel;
 import java.nio.channels.ReadableByteChannel;
 import java.nio.charset.StandardCharsets;
+import java.nio.file.Path;
+import java.text.MessageFormat;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 
 import com.google.common.io.ByteSource;
 import com.google.common.io.CharSource;
+import io.swagger.v3.parser.core.models.ParseOptions;
 import io.swagger.v3.parser.util.ClasspathHelper;
 import org.apache.commons.io.FileUtils;
 import org.apache.commons.lang3.StringUtils;
@@ -52,6 +60,7 @@
 import org.apache.maven.plugins.annotations.Component;
 import org.apache.maven.project.MavenProject;
 
+import org.apache.maven.project.MavenProjectHelper;
 import org.openapitools.codegen.CliOption;
 import org.openapitools.codegen.ClientOptInput;
 import org.openapitools.codegen.CodegenConfig;
@@ -139,6 +148,18 @@ public class CodeGenMojo extends AbstractMojo {
     @Parameter(name = "gitRepoId", property = "openapi.generator.maven.plugin.gitRepoId")
     private String gitRepoId;
 
+    /**
+     * The path to the collapsed single-file representation of the OpenAPI spec.
+     */
+    @Parameter(name = "collapsedSpec", property = "openapi.generator.maven.plugin.collapsedSpec")
+    private String collapsedSpec;
+
+    /**
+     * Includes the collapsed spec in the Maven artifacts.
+     */
+    @Parameter(name = "includeCollapsedSpecInArtifacts", property = "openapi.generator.maven.plugin.publishCollapsedSpec", defaultValue = "false")
+    private boolean includeCollapsedSpecInArtifacts;
+
     /**
      * Folder containing the template files.
      */
@@ -509,6 +530,18 @@ public class CodeGenMojo extends AbstractMojo {
     @Parameter(property = "codegen.configHelp")
     private boolean configHelp = false;
 
+    /**
+     * The Maven project context.
+     */
+    @Parameter(defaultValue = "${project}", required = true, readonly = true)
+    MavenProject mavenProject;
+
+    /**
+     * Maven ProjectHelper used to manage build artifacts.
+     */
+    @Component
+    MavenProjectHelper mavenProjectHelper;
+
     @Parameter(defaultValue = "${mojoExecution}", readonly = true)
     private MojoExecution mojo;
 
@@ -538,6 +571,17 @@ public void execute() throws MojoExecutionException {
                             "generated-test-sources/openapi" : "generated-sources/openapi");
         }
 
+        if (collapsedSpec != null) {
+            final var collapsedSpecPath = createCollapsedSpec();
+            if (includeCollapsedSpecInArtifacts) {
+                mavenProjectHelper.attachArtifact(
+                        mavenProject,
+                        collapsedSpecPath.toString().toLowerCase(Locale.ROOT).endsWith(".json") ? "json" : "yaml",
+                        collapsedSpec,
+                        collapsedSpecPath.toFile());
+            }
+        }
+
         addCompileSourceRootIfConfigured();
 
         try {
@@ -1094,4 +1138,27 @@ private void adjustAdditionalProperties(final CodegenConfig config) {
             }
         }
     }
+
+    private Path createCollapsedSpec() throws MojoExecutionException {
+        // Merge the OpenAPI spec file.
+        final var parseOptions = new ParseOptions();
+        parseOptions.setResolve(true);
+        final var openApiMerged = new OpenAPIResolver(new OpenAPIV3Parser().readLocation(inputSpec, null, parseOptions).getOpenAPI()).resolve();
+
+        // Switch based on JSON or YAML.
+        final var extension = inputSpec.toLowerCase(Locale.ROOT).endsWith(".json") ? ".json" : ".yaml";
+        final var mapper = inputSpec.toLowerCase(Locale.ROOT).endsWith(".json") ? Json.mapper() : Yaml.mapper();
+
+        // Write the merged spec to the output file.
+        final var collapsedSpecPath = output.toPath().resolve(collapsedSpec + extension).toAbsolutePath();
+        try {
+            final var openApiString = mapper.writeValueAsString(openApiMerged);
+            FileUtils.writeStringToFile(collapsedSpecPath.toFile(), openApiString, StandardCharsets.UTF_8);
+        } catch (final IOException e) {
+            throw new MojoExecutionException(new MessageFormat("Failed to write collapsed spec {0}", Locale.ROOT).format(collapsedSpecPath), e);
+        }
+
+        // Return the path to the collapsed spec file.
+        return collapsedSpecPath;
+    }
 }

modules/openapi-generator-maven-plugin/src/test/java/org/openapitools/codegen/plugin/CodeGenMojoTest.java

@@ -21,9 +21,12 @@
 import java.nio.file.Path;
 import java.util.Arrays;
 import java.util.Comparator;
+import java.util.List;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.apache.commons.io.FileUtils;
+import org.apache.maven.artifact.Artifact;
 import org.apache.maven.execution.DefaultMavenExecutionRequest;
 import org.apache.maven.execution.MavenExecutionRequest;
 import org.apache.maven.execution.MavenSession;
@@ -150,6 +153,34 @@ public void testSkipRegenerationForClasspathSpecFileWithChange() throws Exceptio
 
     }
 
+    public void testCollapsedSpecProduced() throws Exception {
+        // GIVEN
+        Path folder = Files.createTempDirectory("test");
+        CodeGenMojo mojo = loadMojo(folder.toFile(), "src/test/resources/default", "executionId");
+
+        // WHEN
+        mojo.execute();
+
+        // THEN
+        File collapseSpecFile = folder.resolve("target/generated-sources/common-maven/remote-openapi/petstore-full-spec.yaml").toFile();
+        assertTrue(collapseSpecFile.exists());
+    }
+
+    public void testCollapsedSpecAddedToArtifacts() throws Exception {
+        // GIVEN
+        Path folder = Files.createTempDirectory("test");
+        CodeGenMojo mojo = loadMojo(folder.toFile(), "src/test/resources/default", "executionId");
+
+        // WHEN
+        mojo.execute();
+
+        // THEN
+        List<Artifact> matchingArtifacts = mojo.mavenProject.getAttachedArtifacts().stream()
+            .filter(artifact -> artifact.getFile().getName().equals("petstore-full-spec.yaml"))
+            .collect(Collectors.toList());
+        assertEquals(1, matchingArtifacts.size());
+    }
+
     protected CodeGenMojo loadMojo(File temporaryFolder, String projectRoot) throws Exception {
         return loadMojo(temporaryFolder, projectRoot, "default");
     }