Use an iterator + collect instead of a for loop

The panics are removed as rust-lang/rust#65785
has made them an error and the compiler will complain anyway for ill
formed attributes.

The use _could_ allow them, technically. But this doesn't really exist:

https://github.com/search?q=allow%28ill_formed_attribute_input%29&type=code

Shows 4 occurences at time of commit. I would also think that users that
enable this, should know what they are doing ;)

Signed-off-by: Marcel Müller <neikos@neikos.email>

Author: TheNeikos

crates/proc_macros/src/util.rs

@@ -1,30 +1,26 @@
-use darling::ToTokens;
 use syn::visit_mut::VisitMut;
-use syn::{Attribute, Expr, GenericArgument, ItemImpl, Lit, Meta, PathArguments, Type, TypePath};
+use syn::{Attribute, Expr, ExprLit, GenericArgument, ItemImpl, Lit, Meta, MetaNameValue, PathArguments, Type, TypePath};
 
 /// From a let of attributes to an item, extracts the ones that are documentation, as strings.
 pub fn extract_doc_lines(attributes: &[Attribute]) -> Vec<String> {
-    let mut docs = Vec::new();
-
-    for attr in attributes {
-        if &attr.path().to_token_stream().to_string() != "doc" {
-            continue;
-        }
-
-        if let Meta::NameValue(x) = &attr.meta {
-            match &x.value {
-                Expr::Lit(x) => match &x.lit {
-                    Lit::Str(x) => {
-                        docs.push(x.value());
-                    }
-                    _ => panic!("Unexpected content in doc string: not a string."),
-                },
-                _ => panic!("Unexpected content in doc string: not a literal."),
+    attributes
+        .iter()
+        .filter_map(|attr| {
+            if !attr.path().is_ident("doc") {
+                return None;
             }
-        }
-    }
 
-    docs
+            let Meta::NameValue(MetaNameValue {
+                value: Expr::Lit(ExprLit { lit: Lit::Str(litstr), .. }),
+                ..
+            }) = &attr.meta
+            else {
+                return None;
+            };
+
+            Some(litstr.value())
+        })
+        .collect()
 }
 
 struct LifetimeRemover;