feat: Add ApiVersion support (#20930)

* feat: Add ApiVersion support

* chore: Update to set the headers in constructor

* chore: Add empty string check

* chore: Update the template

* chore: Remove not needed file

* chore: Add comment for API_VERSION

generator/src/googleapis/codegen/api.py

@@ -685,6 +685,10 @@ def __init__(self, api, name, def_dict, parent=None):
     # TODO(user): if rest_path is not set, raise a good error and fail fast.
     self.SetTemplateValue('restPath', rest_path)
 
+    # Check that ApiVersion field exists and is not empty string ("")
+    if 'apiVersion' in def_dict and def_dict.get('apiVersion'):
+      self.SetTemplateValue('apiVersion', def_dict.get('apiVersion'))
+
     # Figure out the input and output types and schemas for this method.
     expected_request = self.values.get('request')
     if expected_request:

generator/src/googleapis/codegen/languages/java/2.0.0/templates/_method.tmpl

@@ -88,6 +88,10 @@ public class {{ method.className }} extends {{ api.className }}Request<{{ method
 
   private static final String REST_PATH = "{{ method.restPath }}";
 
+  {% if method.apiVersion %}
+  private static final String API_VERSION = "{{ method.apiVersion }}";
+  {% endif %}
+
   {% for param in method.parameters %}
     {% if param.pattern %}
   private final java.util.regex.Pattern {{ param.constantName }}_PATTERN =
@@ -136,6 +140,13 @@ public class {{ method.className }} extends {{ api.className }}Request<{{ method
   {% if method.supportsMediaDownload %}
     initializeMediaDownload();
   {% endif %}
+  {% if method.apiVersion %}
+    // Does not override the API_VERSION if already configured
+    com.google.api.client.http.HttpHeaders headers = getRequestHeaders();
+    if (headers.get(API_VERSION_HEADER) == null) {
+      headers.set(API_VERSION_HEADER, API_VERSION);
+    }
+  {% endif %}
   }
 {% endfilter %}
 
@@ -184,6 +195,13 @@ public class {{ method.className }} extends {{ api.className }}Request<{{ method
     com.google.api.client.util.Preconditions.checkNotNull(mediaContent, "Required parameter mediaContent must be specified.");
     initializeMediaUpload(mediaContent);
   {% call_template _alt_def method=method %}
+  {% if method.apiVersion %}
+    // Does not override the API_VERSION if already configured
+    com.google.api.client.http.HttpHeaders headers = getRequestHeaders();
+    if (headers.get(API_VERSION_HEADER) == null) {
+      headers.set(API_VERSION_HEADER, API_VERSION);
+    }
+  {% endif %}
   }
 {% endif %}
 {% endfilter %}