Implement From for structs

impl/src/expand.rs

@@ -89,12 +89,25 @@ fn impl_struct(input: Struct) -> TokenStream {
         }
     });
 
+    let from_impl = input.from_field().map(|from_field| {
+        let member = &from_field.member;
+        let from = from_field.ty;
+        quote! {
+            impl #impl_generics std::convert::From<#from> for #ty #ty_generics #where_clause {
+                fn from(source: #from) -> Self {
+                    #ty { #member: source }
+                }
+            }
+        }
+    });
+
     quote! {
         impl #impl_generics std::error::Error for #ty #ty_generics #where_clause {
             #source_method
             #backtrace_method
         }
         #display_impl
+        #from_impl
     }
 }
 

impl/src/prop.rs

@@ -2,6 +2,10 @@ use crate::ast::{Enum, Field, Struct, Variant};
 use syn::{Member, Type};
 
 impl Struct<'_> {
+    pub(crate) fn from_field(&self) -> Option<&Field> {
+        from_field(&self.fields)
+    }
+
     pub(crate) fn source_field(&self) -> Option<&Field> {
         source_field(&self.fields)
     }
@@ -43,6 +47,15 @@ impl Variant<'_> {
     }
 }
 
+fn from_field<'a, 'b>(fields: &'a [Field<'b>]) -> Option<&'a Field<'b>> {
+    for field in fields {
+        if field.attrs.from.is_some() {
+            return Some(&field);
+        }
+    }
+    None
+}
+
 fn source_field<'a, 'b>(fields: &'a [Field<'b>]) -> Option<&'a Field<'b>> {
     for field in fields {
         if field.attrs.from.is_some() || field.attrs.source.is_some() {