refactor: improve types of content negotiation methods

Author: thetutlage

adonis-typings/request.ts

@@ -52,13 +52,13 @@ declare module '@ioc:Adonis/Core/Request' {
     url (includeQueryString?: boolean): string
     completeUrl (includeQueryString?: boolean): string
     is (types: string[]): string | null
-    accepts (types: string[]): string | null
+    accepts <T extends string> (types: T[]): T | null
     types (): string[]
-    language (languages: string[]): string | null
+    language <T extends string> (languages: T[]): T | null
     languages (): string[]
-    encoding (encodings: string[]): string | null
+    encoding <T extends string> (encodings: T[]): T | null
     encodings (): string[]
-    charset (charsets: string[]): string | null
+    charset <T extends string> (charsets: T[]): T | null
     charsets (): string[]
     hasBody (): boolean
     fresh (): boolean

src/Request/index.ts

@@ -620,7 +620,7 @@ export class Request extends Macroable implements RequestContract {
    * }
    * ```
    */
-  public accepts (types: string[]): string | null {
+  public accepts <T extends string> (types: T[]): T | null {
     this.initiateAccepts()
     return this.lazyAccepts.type(types) || null
   }
@@ -658,7 +658,7 @@ export class Request extends Macroable implements RequestContract {
    * }
    * ```
    */
-  public language (languages: string[]): string | null {
+  public language <T extends string> (languages: T[]): T | null {
     this.initiateAccepts()
     return this.lazyAccepts.language(languages) || null
   }
@@ -694,7 +694,7 @@ export class Request extends Macroable implements RequestContract {
    * }
    * ```
    */
-  public charset (charsets: string[]): string | null {
+  public charset <T extends string> (charsets: T[]): T | null {
     this.initiateAccepts()
     return this.lazyAccepts.charset(charsets) || null
   }
@@ -720,7 +720,7 @@ export class Request extends Macroable implements RequestContract {
    * Make sure to check [accepts](https://www.npmjs.com/package/accepts) package
    * docs too.
    */
-  public encoding (encodings: string[]): string | null {
+  public encoding <T extends string> (encodings: T[]): T | null {
     this.initiateAccepts()
     return this.lazyAccepts.encoding(encodings) || null
   }