eval: Use better error messages when failing to dump values

Examples:

    let g:SR = [[]]
    call add(g:SR[0], g:SR)
    wshada
    " E952: Unable to dump variable g:SR: container references itself in index 0, index 0

    let g:F = {'_TYPE': v:msgpack_types.map, '_VAL': [[{'abc': 1}, function("tr")]]}
    wshada
    " E951: Error while dumping variable g:F, key {'abc': 1} at index 0 from special map, key '': attempt to dump function reference
    " (no msgpack#string available)
    " E951: Error while dumping variable g:F, key {="abc": 1} at index 0 from special map, key '': attempt to dump function reference
    " (msgpack#string available)

    let g:F = {'_TYPE': v:msgpack_types.map, '_VAL': [[g:SR, function("tr")]]}
    wshada
    " E951: Error while dumping variable g:F, key [[[[{E724@0}]]]] at index 0 from special map, index 1: attempt to dump function reference

    call msgpackdump([g:SR])
    " E952: Unable to dump msgpackdump() argument, index 0: container references itself in index 0, index 0

Not tested yet.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/nvim/eval.h b/src/nvim/eval.h
index 19a1bbb083..ea8b5bc253 100644
--- a/src/nvim/eval.h
+++ b/src/nvim/eval.h
@@ -118,7 +118,8 @@ enum {
 /// Maximum number of function arguments
 #define MAX_FUNC_ARGS   20
 
-int vim_to_msgpack(msgpack_packer *const, typval_T *const);
+int vim_to_msgpack(msgpack_packer *const, typval_T *const,
+                   const char *const objname);
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "eval.h.generated.h"