[cli][doc] Document batch command (#4572)

* [cli][batch] Better glob support

If invoked as `openapi-generator batch *.yaml`, the command might
previously fail in some shells where `*.yaml` expands to file name only.

This supports globs without path-part in the filename to prevent
possible NPE.

* [cli] Document batch command

docs/usage.md

@@ -557,3 +557,85 @@ The name of the file should be `config.yml` or `config.yaml` (in our example it
 openapi-generator generate -i petstore.yaml -g typescript-fetch -o out \
     -c config.yaml
 ```
+
+
+## batch
+
+The `batch` command allows you to move all CLI arguments supported by the `generate` command into a YAML or JSON file.
+
+*NOTE*: This command supports an additional `!include` property which may point to another "shared" file, the base path to which can be
+modified by `--includes-base-dir`.
+
+```bash
+openapi-generator help batch
+NAME
+        openapi-generator-cli batch - Generate code in batch via external
+        configs.
+
+SYNOPSIS
+        openapi-generator-cli batch [--fail-fast]
+                [--includes-base-dir <includes>] [(-r <threads> | --threads <threads>)]
+                [--root-dir <root>] [--timeout <timeout>] [(-v | --verbose)] [--]
+                <configs>...
+
+OPTIONS
+        --fail-fast
+            fail fast on any errors
+
+        --includes-base-dir <includes>
+            base directory used for includes
+
+        -r <threads>, --threads <threads>
+            thread count
+
+        --root-dir <root>
+            root directory used output/includes (includes can be overridden)
+
+        --timeout <timeout>
+            execution timeout (minutes)
+
+        -v, --verbose
+            verbose mode
+
+        --
+            This option can be used to separate command-line options from the
+            list of argument, (useful when arguments might be mistaken for
+            command-line options
+
+        <configs>
+            Generator configuration files.
+```
+
+Example:
+
+```bash
+# create "shared" config
+mkdir shared && cat > shared/common.yaml <<EOF
+inputSpec: https://raw.githubusercontent.com/OpenAPITools/openapi-generator/master/modules/openapi-generator/src/test/resources/2_0/petstore.yaml
+additionalProperties:
+    x-ext-name: "Your Name"
+EOF
+
+# create "standard" configs
+cat > kotlin.yaml <<EOF
+'!include': 'shared/common.yaml'
+outputDir: out/kotlin
+generatorName: kotlin
+artifactId: kotlin-petstore-string
+additionalProperties:
+  dateLibrary: string
+  serializableModel: "true"
+EOF
+
+cat > csharp.yaml <<EOF
+'!include': 'shared/common.yaml'
+outputDir: out/csharp-netcore
+generatorName: csharp-netcore
+additionalProperties:
+  packageGuid: "{321C8C3F-0156-40C1-AE42-D59761FB9B6C}"
+  useCompareNetObjects: "true"
+EOF
+
+# Generate them
+openapi-generator batch *.yaml
+```

modules/openapi-generator-cli/src/main/java/org/openapitools/codegen/cmd/GenerateBatch.java

@@ -39,6 +39,7 @@ import org.slf4j.LoggerFactory;
 
 import java.io.File;
 import java.io.IOException;
+import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.List;
@@ -100,16 +101,6 @@ public class GenerateBatch implements Runnable {
             numThreads = threads;
         }
 
-        // This allows us to put meta-configs in a different file from referenced configs.
-        // If not specified, we'll assume it's the parent directory of the first file.
-        File includesDir;
-        if (includes != null) {
-            includesDir = new File(includes);
-        } else {
-            Path first = Paths.get(configs.get(0));
-            includesDir = first.getParent().toFile();
-        }
-
         Path rootDir;
         if (root != null) {
             rootDir = Paths.get(root);
@@ -117,7 +108,23 @@ public class GenerateBatch implements Runnable {
             rootDir = Paths.get(System.getProperty("user.dir"));
         }
 
-        LOGGER.info(String.format(Locale.ROOT, "Batch generation using %d threads.\nIncludes: %s\nRoot: %s", numThreads, includesDir.getAbsolutePath(), rootDir.toAbsolutePath().toString()));
+        // This allows us to put meta-configs in a different file from referenced configs.
+        // If not specified, we'll assume it's the parent directory of the first file.
+        File includesDir;
+        if (includes != null) {
+            includesDir = new File(includes);
+        } else {
+            Path first = Paths.get(configs.get(0));
+            if (Files.isRegularFile(first) && !Files.isSymbolicLink(first)) {
+                includesDir = first.toAbsolutePath().getParent().toFile();
+            } else {
+                // Not traversing symbolic links for includes. Falling back to rooted working directory.
+                includesDir = rootDir.toFile();
+            }
+        }
+
+
+        LOGGER.info(String.format(Locale.ROOT, "Batch generation using up to %d threads.\nIncludes: %s\nRoot: %s", numThreads, includesDir.getAbsolutePath(), rootDir.toAbsolutePath().toString()));
 
         // Create a module which loads our config files, but supports a special "!include" key which can point to an existing config file.
         // This allows us to create a sort of meta-config which holds configs which are otherwise required at CLI time (via generate task).