Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When generating Go client code for an endpoint that accepts an array of binary files (e.g., type: array, items: {type: string, format: binary}), the generator fails to add the import "os" statement to the generated API file, even though the parameter type is []*os.File. This results in a compilation error in the generated Go code.

The same issue affects array parameters with format: date-time, where the import "time" statement is missing.

openapi-generator version

7.18.0-SNAPSHOT (master branch as of November 19, 2025)

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  title: Test API
  version: 1.0.0
paths:
  '/upload':
    post:
      operationId: uploadFiles
      requestBody:
        required: true
        content:
          multipart/mixed:
            schema:
              type: object
              properties:
                files:
                  type: array
                  items:
                    type: string
                    format: binary
      responses:
        '200':
          description: Success
  '/events':
    get:
      operationId: getEvents
      parameters:
        - name: timestamps
          in: query
          schema:
            type: array
            items:
              type: string
              format: date-time
      responses:
        '200':
          description: Success

Generation Details

openapi-generator-cli generate \
    --additional-properties packageName=client \
    --additional-properties withGoCodegenComment=true \
    -i test-binary-array.yaml \
    -g go \
    -o ./generated

Steps to reproduce

1. Create an OpenAPI spec with an endpoint that has an array parameter with format: binary (see example above)
2. Generate Go client code using the go generator
3. Check the generated API file (e.g., api_default.go) - notice it's missing import "os"
4. Try to compile the generated code:

   cd generated
   go build

5. Compilation fails with error:

./api_default.go:29:16: undefined: time
./api_default.go:32:54: undefined: time
./api_default.go:132:11: undefined: os
./api_default.go:135:47: undefined: os

Related issues/PRs

Issues containing os.File:
https://github.com/OpenAPITools/openapi-generator/search?q=os.File&type=Issues

Open issues are very old, some might apply, but are very outdated.

Similar issues may exist for other array-based type mappings

Suggest a fix

Root Cause:
In AbstractGoCodegen.java, the methods postProcessOperationsWithModels() and postProcessWebhooksWithModels() only check if param.dataType equals "*os.File" or "time.Time". This works for single file/datetime parameters but fails for arrays.

For array parameters:

• Single file: param.dataType = "*os.File" ✓
• Array of files: param.dataType = "[]*os.File", but param.items.dataType = "*os.File" ✗

Solution:
The import detection logic needs to also check param.items.dataType for array parameters, similar to how it's already correctly implemented in postProcessModels() for model properties.

Required changes in AbstractGoCodegen.java:

1. In postProcessOperationsWithModels() method (~line 550):

// OLD CODE:
if (!addedOSImport && "*os.File".equals(param.dataType)) {
    imports.add(createMapping("import", "os"));
    addedOSImport = true;
}

if (!addedTimeImport && "time.Time".equals(param.dataType)) {
    imports.add(createMapping("import", "time"));
    addedTimeImport = true;
}

// NEW CODE:
if (!addedOSImport && ("*os.File".equals(param.dataType) ||
        (param.items != null && "*os.File".equals(param.items.dataType)))) {
    imports.add(createMapping("import", "os"));
    addedOSImport = true;
}

if (!addedTimeImport && ("time.Time".equals(param.dataType) ||
        (param.items != null && "time.Time".equals(param.items.dataType)))) {
    imports.add(createMapping("import", "time"));
    addedTimeImport = true;
}

2. In postProcessWebhooksWithModels() method (~line 651): Apply the same change

Why this works:

• For single parameters, param.dataType is checked directly
• For array parameters, param.items contains the element type information
• This aligns with the existing correct implementation in postProcessModels() (line ~780)

I will provide a PR with the fix