Libguestfs - Feb 2020 - [PATCH] golang: make API idiomatic so that functions return (<val>, error)

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

On Wed, Feb 19, 2020 at 02:30:45PM +0100, Csaba Henk
wrote:
> 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.
Thanks - pushed.

The bindtests fail with a rather obscure error.  I don't know what it
means or if it's related to this patch.

=============================================   libguestfs 1.41.8:
golang/test-suite.log
=============================================
# TOTAL: 2
# PASS:  1
# SKIP:  0
# XFAIL: 0
# FAIL:  1
# XPASS: 0
# ERROR: 0

.. contents:: :depth: 2

FAIL: run-bindtests
==================
panic: runtime error: cgo argument has Go pointer to Go pointer

goroutine 1 [running]:
libguestfs.org/guestfs.(*Guestfs).Internal_test.func7(0xc000010028, 0x107a430,
0x1078a20, 0xc000010050, 0xc000000000, 0x0, 0x0, 0x1079ec0, 0x1075190,
0x10751b0, ...)
	/home/rjones/d/libguestfs/golang/src/libguestfs.org/guestfs/guestfs.go:6667
+0xf7
libguestfs.org/guestfs.(*Guestfs).Internal_test(0xc000010028, 0x4f3f43, 0x3,
0xc000063b90, 0xc000063aa0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
	/home/rjones/d/libguestfs/golang/src/libguestfs.org/guestfs/guestfs.go:6667
+0x3cc
main.main()
	/home/rjones/d/libguestfs/golang/bindtests.go:77 +0x127d
exit status 2
FAIL run-bindtests (exit status: 1)


Rich.

-- 
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