Add context to code suggestions API

What does this MR do and why?

Adds context to code completion API

Add a context param to /code_suggestions/completions API. The context is an array of object with the following fields:

• type - The type of the content. Can be either 'file' or 'function'.
• name - The name of the content. File name for files, and function name for functions.
• content - The content itself. The file or a code snippet

Contributes to https://gitlab.com/gitlab-org/editor-extensions/gitlab-lsp/-/issues/208

MR acceptance checklist

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How to set up and validate locally

Let's assume the codebase consists of 3 files. FullName method, intentionally implemented in an unusually way, to demonstrate that the context improves code suggestions.

user.go file

package main

type User struct {
	Title string
	First string
	Last  string
}

func (u User) FullName(withTitle bool) string {
	fullName := u.First + " " + u.Last

	if withTitle {
		fullName = u.Title + ". " + fullName
	}

	return fullName
}

main.go file

package main

import "fmt"

func main() {
	user := User{"Mr", "John", "Doe"}
	fmt.Printf("Full name: %s\n", user.FullName(true))
}

user_test.go file

package main

import "testing"

// Write test for User FullName

Request without context

curl --request POST \
     --url http://gdk.test:3000/api/v4/code_suggestions/completions \
     --header 'Content-Type: application/json' \
     --header "Private-Token: $LOCALHOST_TOKEN" \
     --data-binary '{
  "current_file": {
    "file_name": "user_test.go",
    "content_above_cursor": "package main\\n\\nimport \"testing\"\\n// Write test for User FullName",
    "content_below_cursor": "\\n"
  },
  "stream": true
}' --no-buffer --location

Response

func TestUserFullName(t *testing.T) {
    user := User{
        FirstName: "John",
        LastName:  "Doe",
    }

    fullName := user.FullName()
    expected := "John Doe"

    if fullName != expected {
        t.Errorf("FullName() = %q, expected %q", fullName, expected)
    }
}

As you can see, the code suggestion is a pure guess. The code is only generated for the function name.

Request with context

curl --request POST \
     --url http://gdk.test:3000/api/v4/code_suggestions/completions \
     --header 'Content-Type: application/json' \
     --header "Private-Token: $LOCALHOST_TOKEN" \
     --data-binary '{
  "current_file": {
    "file_name": "user_test.go",
    "content_above_cursor": "package main\\n\\nimport \"testing\"\\n// Write test for User FullName",
    "content_below_cursor": "\\n"
  },
  "stream": true,
  "instruction": "Write test for User FullName function",
  "context": [
    { "type": "file", "name": "user.go", "content": "package main\n\ntype User struct {\n\tTitle string\n\tFirst string\n\tLast  string\n}\n\nfunc (u User) FullName(withTitle bool) string {\n\tfullName := u.First + \" \" + u.Last\n\n\tif withTitle {\n\t\tfullName = u.Title + \". \" + fullName\n\t}\n\n\treturn fullName\n}\n" },
    { "type": "file", "name": "main.go", "content": "package main\n\nimport \"fmt\"\n\nfunc main() {\n\tuser := User{\"Mr\", \"John\", \"Doe\"}\n\tfmt.Printf(\"Full name: %s\\n\", user.FullName(true))\n}\n" }
  ]
}' --no-buffer --location

Response

Now with an additional context we managed to generate correct code for your weirdly implemented function.

func TestUserFullName(t *testing.T) {
	user := User{"Mr", "John", "Doe"}

	fullName := user.FullName(true)
	expected := "Mr. John Doe"
	if fullName != expected {
		t.Errorf("FullName(true) = %s; expected %s", fullName, expected)
	}

	fullName = user.FullName(false)
	expected = "John Doe"
	if fullName != expected {
		t.Errorf("FullName(false) = %s; expected %s", fullName, expected)
	}
}