Added from type info to cast errors

src/errors.rs

@@ -30,7 +30,7 @@ pub enum Error {
     /// Step was out of range for usize on this platform
     StepSizeOutOfRange(i32),
     /// A numeric cast from `value` failed during `task`
-    NumericCastFailed {
+    CastFromI32Failed {
         source: std::num::TryFromIntError,
         task: ErrorTask,
         value: usize,
@@ -72,7 +72,7 @@ impl std::error::Error for Error {
         match &self {
             NullInStr(err) => Some(err),
             CouldNotCheckNAtoms(err) => Some(err.as_ref()),
-            NumericCastFailed { source, .. } => Some(source),
+            CastFromI32Failed { source, .. } => Some(source),
             _ => None,
         }
     }
@@ -135,9 +135,9 @@ impl std::fmt::Display for Error {
                 write!(f, "Failed to read number of atoms in trajectory file")
             }
             StepSizeOutOfRange(n) => write!(f, "Step {} does not fit in usize on this platform", n),
-            NumericCastFailed { value, task, .. } => write!(
+            CastFromI32Failed { value, task, .. } => write!(
                 f,
-                "Numeric cast from {value} failed while {task}",
+                "Numeric cast from {value}:usize to i32 failed while {task}",
                 value = value,
                 task = task
             ),

src/lib.rs

@@ -109,7 +109,7 @@ fn path_to_cstring(path: impl AsRef<Path>) -> Result<CString> {
 }
 
 fn to_i32(value: usize, task: ErrorTask) -> Result<i32> {
-    value.try_into().map_err(|e| Error::NumericCastFailed {
+    value.try_into().map_err(|e| Error::CastFromI32Failed {
         source: e,
         value,
         task,
@@ -809,7 +809,7 @@ mod tests {
             Err(e) => e,
             _ => panic!("Conversion from -1 to u8 succeeded"),
         };
-        let expected = Error::NumericCastFailed {
+        let expected = Error::CastFromI32Failed {
             source: try_from_int_err,
             task: ErrorTask::Write,
             value: 3_294_967_295_usize,