data: add structured error in exception

libyang/context.py

@@ -16,7 +16,15 @@
     validation_flags,
 )
 from .schema import Module, SNode, schema_in_format
-from .util import DataType, IOType, LibyangError, c2str, data_load, str2c
+from .util import (
+    DataType,
+    IOType,
+    LibyangError,
+    LibyangErrorItem,
+    c2str,
+    data_load,
+    str2c,
+)
 
 
 # -------------------------------------------------------------------------------------
@@ -284,23 +292,35 @@ def __exit__(self, *args, **kwargs):
         self.destroy()
 
     def error(self, msg: str, *args) -> LibyangError:
-        msg %= args
+        if args:
+            msg = msg % args
+
+        parts = [msg]
+        errors = []
 
         if self.cdata:
             err = lib.ly_err_first(self.cdata)
             while err:
-                if err.msg:
-                    msg += ": %s" % c2str(err.msg)
-                if err.data_path:
-                    msg += ": Data path: %s" % c2str(err.data_path)
-                if err.schema_path:
-                    msg += ": Schema path: %s" % c2str(err.schema_path)
-                if err.line != 0:
-                    msg += " (line %u)" % err.line
+                m = c2str(err.msg) if err.msg else None
+                dp = c2str(err.data_path) if err.data_path else None
+                sp = c2str(err.schema_path) if err.schema_path else None
+                ln = int(err.line) if err.line else None
+                parts.extend(
+                    tmpl.format(val)
+                    for val, tmpl in [
+                        (m, ": {}"),
+                        (dp, ": Data path: {}"),
+                        (sp, ": Schema path: {}"),
+                        (ln, " (line {})"),
+                    ]
+                    if val is not None
+                )
+                errors.append(LibyangErrorItem(m, dp, sp, ln))
                 err = err.next
             lib.ly_err_clean(self.cdata, ffi.NULL)
 
-        return LibyangError(msg)
+        msg = "".join(parts)
+        return LibyangError(msg, errors=errors)
 
     def parse_module(
         self,

libyang/util.py

@@ -2,16 +2,34 @@
 # Copyright (c) 2021 RACOM s.r.o.
 # SPDX-License-Identifier: MIT
 
+from dataclasses import dataclass
 import enum
-from typing import Optional
+from typing import Iterable, Optional
 import warnings
 
 from _libyang import ffi, lib
 
 
+# -------------------------------------------------------------------------------------
+@dataclass(frozen=True)
+class LibyangErrorItem:
+    msg: Optional[str]
+    data_path: Optional[str]
+    schema_path: Optional[str]
+    line: Optional[int]
+
+
 # -------------------------------------------------------------------------------------
 class LibyangError(Exception):
-    pass
+    def __init__(
+        self, message: str, *args, errors: Optional[Iterable[LibyangErrorItem]] = None
+    ):
+        super().__init__(message, *args)
+        self.message = message
+        self.errors = tuple(errors or ())
+
+    def __str__(self):
+        return self.message
 
 
 # -------------------------------------------------------------------------------------

tests/test_data.py

@@ -289,6 +289,18 @@ def test_data_parse_config_xml_multi_error(self):
             "Data path: /yolo-system:conf/url[proto='https'] (line 7)",
         )
 
+        first = cm.exception.errors[0]
+        self.assertEqual(first.msg, 'Invalid boolean value "abcd".')
+        self.assertEqual(
+            first.data_path, "/yolo-system:conf/url[proto='https']/enabled"
+        )
+        self.assertEqual(first.line, 6)
+
+        second = cm.exception.errors[1]
+        self.assertEqual(second.msg, 'List instance is missing its key "host".')
+        self.assertEqual(second.data_path, "/yolo-system:conf/url[proto='https']")
+        self.assertEqual(second.line, 7)
+
     XML_STATE = """<state xmlns="urn:yang:yolo:system">
   <hostname>foo</hostname>
   <url>