Improve error messages for compile errors caused by the expression specified in #[from_str(with = ..)].

Author: frozenlib

parse-display-derive/src/lib.rs

@@ -618,7 +618,7 @@ impl<'a> ParserBuilder<'a> {
                     },
                 ) in self.with.iter().enumerate()
                 {
-                    with.push(quote! {
+                    with.push(quote_spanned! {expr.span()=>
                         (#capture, #helpers::to_ast::<#ty, _>(&#expr))
                     });
                     let msg = format!(
@@ -1699,14 +1699,23 @@ fn build_parse_capture_expr(
         if let Some(with) = &field.hattrs.with {
             let ty = &field.source.ty;
             expr1 = quote! {
-                #crate_path::helpers::parse_with::<#ty, _ >(#with, #expr0)
+                #crate_path::helpers::parse_with::<#ty, _>(#with, #expr0)
             };
+            expr1 = set_span(expr1, with.span());
         }
     }
     quote! {
         #expr1.map_err(|e| #crate_path::ParseError::with_message(#msg))?
     }
 }
+fn set_span(ts: TokenStream, span: Span) -> TokenStream {
+    ts.into_iter()
+        .map(|mut ts| {
+            ts.set_span(span);
+            ts
+        })
+        .collect()
+}
 
 fn unref_ty(ty: &Type) -> Type {
     if let Type::Reference(ty) = ty {

parse-display/tests/compile_fail/from_str/invalid_with.rs

@@ -0,0 +1,9 @@
+use parse_display::FromStr;
+
+#[derive(FromStr, Debug, PartialEq)]
+struct X {
+    #[from_str(with = "not impl FromStrFormat")]
+    x: u8,
+}
+
+fn main() {}

parse-display/tests/compile_fail/from_str/invalid_with.stderr

@@ -0,0 +1,7 @@
+error[E0277]: the trait bound `&'static str: FromStrFormat<u8>` is not satisfied
+ --> tests/compile_fail/from_str/invalid_with.rs:5:23
+  |
+5 |     #[from_str(with = "not impl FromStrFormat")]
+  |                       ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromStrFormat<u8>` is not implemented for `&'static str`
+  |
+  = note: required for the cast from `&&'static str` to `&dyn FromStrFormat<u8, Err = _>`