wip: Reduce test differences [ci-skip]

 - Handle UTF-16 surrogate pairs
 - Handle cycles in values
 - Handle cycles in types
 - Better errors
 - Handle case-folding of struct field names
 - Allow []byteTypeWithMethods
 - Fix struct field-order
 - Fix handling of interfaces storing pointers
 - Enforce a maximum decode depth
 - Validate struct tags

1 files changed, 130 insertions, 0 deletions

diff --git a/errors.go b/errors.go
new file mode 100644
index 0000000..a5a4080
--- /dev/null
+++ b/errors.go
@@ -0,0 +1,130 @@
+// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package lowmemjson
+
+import (
+	"encoding/json"
+	"fmt"
+	"reflect"
+	"strings"
+	"errors"
+)
+
+// low-level decode errors /////////////////////////////////////////////////////////////////////////
+// These will be wrapped in a *DecodeError.
+
+// A *DecodeReadError is returned from Decode if there is an I/O error
+// reading the input.
+type DecodeReadError struct {
+	Err    error
+	Offset int64
+}
+
+func (e *DecodeReadError) Error() string {
+	return fmt.Sprintf("json: I/O error at input byte %v: %v", e.Offset, e.Err)
+}
+func (e *DecodeReadError) Unwrap() error { return e.Err }
+
+// A *DecodeSyntaxError is returned from Decode if there is a syntax
+// error in the input.
+type DecodeSyntaxError struct {
+	Err    error
+	Offset int64
+}
+
+func (e *DecodeSyntaxError) Error() string {
+	return fmt.Sprintf("json: syntax error at input byte %v: %v", e.Offset, e.Err)
+}
+
+// A *DecodeTypeError is returned from Decode if the JSON input is not
+// appropriate for the given Go type.
+//
+// If a .DecodeJSON, .UnmarshalJSON, or .UnmashaleText method returns
+// an error, it is wrapped in a *DecodeTypeError.
+type DecodeTypeError struct {
+	JSONType string //  (optional)
+	GoType   reflect.Type
+	Offset   int64
+	Err      error // (optional)
+}
+
+func (e *DecodeTypeError) Error() string {
+	var buf strings.Builder
+	buf.WriteString("json: cannot decode ")
+	if e.JSONType != "" {
+		fmt.Fprintf(&buf, "JSON %s ", e.JSONType)
+	}
+	fmt.Fprintf(&buf, "at input byte %v in to Go %v", e.Offset, e.GoType)
+	if e.Err != nil {
+		fmt.Fprintf(&buf, ": %v", strings.TrimPrefix(e.Err.Error(), "json: "))
+	}
+	return buf.String()
+}
+
+func (e *DecodeTypeError) Unwrap() error { return e.Err }
+
+var ErrDecodeExceededMaxDepth = errors.New("exceeded max depth")
+
+// high-level decode errors ////////////////////////////////////////////////////////////////////////
+
+// A *DecodeArgumentError is returned from Decode if the argument is
+// not a non-nil pointer or is not settable.
+//
+// Alternatively, a *DecodeArgument error may be found inside of a
+// *DecodeTypeError if the type being decoded in to is not a type that
+// can be decoded in to (such as map with non-stringable type as
+// keys).
+//
+//	type DecodeArgumentError struct {
+//	    Type reflect.Type
+//	}
+type DecodeArgumentError = json.InvalidUnmarshalError
+
+type DecodeError struct {
+	Field string
+	Err   error
+
+	FieldParent string // for compat
+	FieldName   string // for compat
+}
+
+func (e *DecodeError) Error() string {
+	return fmt.Sprintf("json: %s: %s", e.Field, strings.TrimPrefix(e.Err.Error(), "json: "))
+}
+func (e *DecodeError) Unwrap() error { return e.Err }
+
+// encode errors ///////////////////////////////////////////////////////////////////////////////////
+
+// An *EncodeTypeError is returned by Encode when attempting to encode
+// an unsupported type.
+//
+//	type EncodeTypeError struct {
+//	    Type reflect.Type
+//	}
+type EncodeTypeError = json.UnsupportedTypeError
+
+// An *EncodeValueError is returned by Encode when attempting to
+// encode an unsupported value (such as a datastructure with a cycle).
+//
+//	type UnsupportedValueError struct {
+//	    Value reflect.Value
+//	    Str   string
+//	}
+type EncodeValueError = json.UnsupportedValueError
+
+// An *EncodeTypeError is returned by Encode when attempting to encode
+// an unsupported value type.
+type EncodeMethodError struct {
+	Type       reflect.Type
+	Err        error
+	SourceFunc string
+}
+
+func (e *EncodeMethodError) Error() string {
+	return fmt.Sprintf("json: error calling %v for type %v: %v",
+		e.SourceFunc, e.Type, strings.TrimPrefix(e.Err.Error(), "json: "))
+}
+
+func (e *EncodeMethodError) Unwrap() error { return e.Err }