[Libguestfs] [PATCH] golang: make API idiomatic so that functions return (<val>, error)

[Csaba Henk]

Go API functions returned (<val>, *GuestfsError) that made
code like this fail to build:

    n, err := os.Stdin.Read(buf)
    if err != nil {
        log.Fatal(err)
    }
    n, err = g.Pwrite_device(dev, buf[:n], off)
    ...

As err should be of error (interface) type as of the stdlib call,
and should be of *GuestfsError type as of the libguestfs call.

The concrete error value that libguestfs functions return can be
a *GuestfsError, but the function signature should have (<val>, error)
as return value.
---
 generator/golang.ml | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/generator/golang.ml b/generator/golang.ml
index bd09ae9cf..e11967d57 100644
--- a/generator/golang.ml
+++ b/generator/golang.ml
@@ -114,6 +114,11 @@ func (e *GuestfsError) String() string {
     }
 }

+/* Implement the error interface */
+func (e *GuestfsError) Error() string {
+     return e.String()
+}
+
 func get_error_from_handle (g *Guestfs, op string) *GuestfsError {
     // NB: DO NOT try to free c_errmsg!
     c_errmsg := C.guestfs_last_error (g.g)
@@ -322,24 +327,24 @@ func return_hashtable (argv **C.char) map[string]string {
       (* Return type. *)
       let noreturn =
         match ret with
-        | RErr -> pr " *GuestfsError"; ""
-        | RInt _ -> pr " (int, *GuestfsError)"; "0, "
-        | RInt64 _ -> pr " (int64, *GuestfsError)"; "0, "
-        | RBool _ -> pr " (bool, *GuestfsError)"; "false, "
+        | RErr -> pr " error"; ""
+        | RInt _ -> pr " (int, error)"; "0, "
+        | RInt64 _ -> pr " (int64, error)"; "0, "
+        | RBool _ -> pr " (bool, error)"; "false, "
         | RConstString _
-        | RString _ -> pr " (string, *GuestfsError)"; "\"\", "
-        | RConstOptString _ -> pr " (*string, *GuestfsError)"; "nil, "
-        | RStringList _ -> pr " ([]string, *GuestfsError)"; "nil, "
+        | RString _ -> pr " (string, error)"; "\"\", "
+        | RConstOptString _ -> pr " (*string, error)"; "nil, "
+        | RStringList _ -> pr " ([]string, error)"; "nil, "
         | RStruct (_, sn) ->
           let sn = camel_name_of_struct sn in
-          pr " (*%s, *GuestfsError)" sn;
+          pr " (*%s, error)" sn;
           sprintf "&%s{}, " sn
         | RStructList (_, sn) ->
           let sn = camel_name_of_struct sn in
-          pr " (*[]%s, *GuestfsError)" sn;
+          pr " (*[]%s, error)" sn;
           "nil, "
-        | RHashtable _ -> pr " (map[string]string, *GuestfsError)"; "nil, "
-        | RBufferOut _ -> pr " ([]byte, *GuestfsError)"; "nil, " in
+        | RHashtable _ -> pr " (map[string]string, error)"; "nil, "
+        | RBufferOut _ -> pr " ([]byte, error)"; "nil, " in

       (* Body of the function. *)
       pr " {\n";
-- 
2.25.1