[librsvg] error.rs: Implement From<ParseError> for AttributeError

[Federico Mena Quintero <federico src gnome org>]

commit bbea658427ff3d3b693fb46f07ea17d4b70c0618
Author: Federico Mena Quintero <federico gnome org>
Date:   Wed Mar 15 20:42:32 2017 -0600

    error.rs: Implement From<ParseError> for AttributeError
    
    This lets us convert a low-level ParseError implicitly to a higher-level
    AttributeError.

 rust/src/error.rs |   27 +++++++++++++++++++++++++++
 1 files changed, 27 insertions(+), 0 deletions(-)
---
diff --git a/rust/src/error.rs b/rust/src/error.rs
index ea07cd1..101f2b7 100644
--- a/rust/src/error.rs
+++ b/rust/src/error.rs
@@ -59,3 +59,30 @@ impl fmt::Display for NodeError {
     }
 }
 
+impl From<ParseError> for AttributeError {
+    fn from (pe: ParseError) -> AttributeError {
+        AttributeError::Parse (pe)
+    }
+}
+
+pub fn is_parse_error<T> (r: &Result<T, AttributeError>) -> bool {
+    if r.is_err () {
+        match r.unwrap_err () {
+            AttributeError::Parse (_) => true,
+            _ => false
+        }
+    } else {
+        false
+    }
+}
+
+pub fn is_value_error<T> (r: &Result<T, AttributeError>) -> bool {
+    if r.is_err () {
+        match r.unwrap_err () {
+            AttributeError::Value (_) => true,
+            _ => false
+        }
+    } else {
+        false
+    }
+}