[Various] -DsupportingFiles generates incorrect code without -Dapis

Description

Information about API operations is only calculated/computed when APIs are being generated, but some targets seem to have lists of operations in their supporting files. These targets cannot generate correctly generate their supporting files when -DsupportingFiles is specified by itself.

This affects the Go client and probably also JavaSpring, Go server, nodejs, and pythonFlaskConnexion.

Swagger-codegen version

3.0.25-SNAPSHOT

Swagger declaration file content or url

There is no specific OpenAPI code that triggers this problem, but here's a test one to make the commands to reproduce more complete.

openapi: 3.0.0
info:
  title: "Example 01"
paths:
  "/mibs/keys":
    get:
      summary: "List all MIB names"
      responses:
        '200':
          description: Successful operation
          content:
            application/json:
              schema:
                type: string

Command line used for generation

java -cp $classpath
io.swagger.codegen.v3.cli.SwaggerCodegen
generate -l go -DsupportingFiles -i example01.yaml -o output/example02

Steps to reproduce

codegen() {
    java -cp $classpath \
	 io.swagger.codegen.v3.cli.SwaggerCodegen \
	 generate "$@"
}
codegen -l go -Dapis            -i example01.yaml -o output/example02 > /dev/null
codegen -l go -DsupportingFiles -i example01.yaml -o output/example02 > /dev/null
codegen -l go -Dmodels          -i example01.yaml -o output/example02 > /dev/null
mkdir -p output/example02/test
cp example01.go output/example02/test/example02.go

cd output/example02
test -f go.mod || go mod init example01
test -f go.sum || go mod tidy
go build test/example02.go || echo Expected failure: "test/example02.go:14:28: client.DefaultApi undefined (type *swagger.APIClient has no field or method DefaultApi)"

The example01.go source file I used to test is here.

package main

import (
	"context"
	"example01" // Gets imported as "swagger"
)

func main() {

	client := swagger.NewAPIClient(swagger.NewConfiguration())
	client.DefaultApi.MibsKeysGet(context.TODO())
}

The client template for Go (main/resources/handlebars/go/client.mustache) has the following two blocks of Handlebars/Mustache code in it

{{#operations}}

        {{classname}} *{{classname}}Service
{{/operations}}

and

{{#operations}}
        c.{{classname}} = (*{{classname}}Service)(&c.common)
{{/operations}}

They expand to nothing unless APIs are being generated.

Related issues/PRs

Suggest a fix/enhancement

The obvious fix is to rewrite the target templates to not use the operations in supporting files. There is no good reason why the Go client target does this. This does change the target interface, but it is slightly cleaner than trying to stop processing the APIs halfway through so that you have all the operations without generating the APIs.

Or you could fiddle with the generateApis private method of the DefaultGenerator class. I will have a PR for this in a few minutes because it's probably the option you are going to pick.

Reproduce the failure with example01.yaml and the supportingFiles-only commands, then inspect main/resources/handlebars/go/client.mustache and DefaultGenerator.generateApis. Compare the generated Go client with the APIs-plus-supportingFiles run; done means supporting files retain the required operations and the resulting example builds successfully.