genai: do not fail with custom HTTP client (#81)

If there is no WithAPIKey option, we were returning an error.
But it's possible that the user provided an alternative HTTP
client that does auth, so don't return an error in that case.

Fixes #80.

genai/client.go

@@ -70,16 +70,22 @@ Import the option package as "google.golang.org/api/option".`)
 	return &Client{c: c, mc: mc}, nil
 }
 
-// hasAPIKey reports whether one of the options was created with
-// WithAPIKey.
-// There is no good way to do that, because the type of the option
-// is unexported, and the struct that it populates is in an internal package.
+// hasAPIKey reports whether the options imply that there is an API key.
+// That is the case if either the WithAPIKey or WithHTTPClient options is present.
+// (If the latter is present, we assume it handles auth).
+//
+// There is no good way to make these checks, because the types of the options
+// are unexported, and the struct that they populates is in an internal package.
 func hasAPIKey(opts []option.ClientOption) bool {
 	for _, opt := range opts {
 		v := reflect.ValueOf(opt)
-		if v.Type().String() == "option.withAPIKey" {
+		ts := v.Type().String()
+		if ts == "option.withAPIKey" {
 			return v.String() != ""
 		}
+		if ts == "option.withHTTPClient" {
+			return true
+		}
 	}
 	return false
 }