Emit error when user writes incorrect format for display attribute (#…

…127, #160)

Additionally:
- set Clippy's MSRV to 1.36.0
- refine Clippy options on CI

.github/workflows/ci.yml

@@ -85,7 +85,7 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: clippy
-          args: --all -- -D clippy::all -D warnings -A clippy::match_like_matches_macro
+          args: --all-features -- -D warnings
 
   rustfmt:
     name: rustfmt

clippy.toml

@@ -0,0 +1 @@
+msrv = "1.36.0"

src/display.rs

@@ -1,4 +1,4 @@
-use std::{fmt::Display, iter::FromIterator as _, str::FromStr as _};
+use std::{fmt::Display, str::FromStr as _};
 
 use proc_macro2::{Ident, Span, TokenStream};
 use quote::{quote, quote_spanned};
@@ -115,7 +115,7 @@ fn trait_name_to_trait_bound(trait_name: &str) -> syn::TraitBound {
         paren_token: None,
         path: syn::Path {
             leading_colon: Some(syn::Token![::](Span::call_site())),
-            segments: syn::punctuated::Punctuated::from_iter(path_segments_iterator),
+            segments: path_segments_iterator.collect(),
         },
     }
 }
@@ -221,34 +221,44 @@ impl<'a, 'b> State<'a, 'b> {
         attrs: &[syn::Attribute],
         meta_key: &str,
     ) -> Result<Option<syn::Meta>> {
-        let mut iterator = attrs
-            .iter()
-            .filter_map(|attr| attr.parse_meta().ok())
-            .filter(|meta| {
-                let meta = match meta {
-                    syn::Meta::List(meta) => meta,
-                    _ => return false,
-                };
-
-                if !meta.path.is_ident(self.trait_attr) || meta.nested.is_empty() {
-                    return false;
-                }
+        let mut metas = Vec::new();
+        for meta in attrs.iter().filter_map(|attr| attr.parse_meta().ok()) {
+            let meta_list = match &meta {
+                syn::Meta::List(meta) => meta,
+                _ => continue,
+            };
 
-                let meta = match &meta.nested[0] {
-                    syn::NestedMeta::Meta(meta) => meta,
-                    _ => return false,
-                };
+            if !meta_list.path.is_ident(self.trait_attr) {
+                continue;
+            }
 
-                let meta = match meta {
-                    syn::Meta::NameValue(meta) => meta,
-                    _ => return false,
-                };
+            use syn::{Meta, NestedMeta};
+            let meta_nv = match meta_list.nested.first() {
+                Some(NestedMeta::Meta(Meta::NameValue(meta_nv))) => meta_nv,
+                _ => {
+                    // If the given attribute is not MetaNameValue, it most likely implies that the
+                    // user is writing an incorrect format. For example:
+                    // - `#[display()]`
+                    // - `#[display("foo")]`
+                    // - `#[display(foo)]`
+                    return Err(Error::new(
+                        meta.span(),
+                        format!(
+                            r#"The format for this attribute cannot be parsed. Correct format: `#[{}({} = "...")]`"#,
+                            self.trait_attr, meta_key
+                        ),
+                    ));
+                }
+            };
 
-                meta.path.is_ident(meta_key)
-            });
+            if meta_nv.path.is_ident(meta_key) {
+                metas.push(meta);
+            }
+        }
 
-        let meta = iterator.next();
-        if iterator.next().is_none() {
+        let mut iter = metas.into_iter();
+        let meta = iter.next();
+        if iter.next().is_none() {
             Ok(meta)
         } else {
             Err(Error::new(meta.span(), "Too many attributes specified"))
@@ -775,7 +785,7 @@ mod regex_maybe_placeholder_spec {
         let fmt_string = "{}, {:?}, {{}}, {{{1:0$}}}";
         let placeholders: Vec<_> = crate::parsing::all_placeholders(&fmt_string)
             .into_iter()
-            .flat_map(|x| x)
+            .flatten()
             .collect();
         assert_eq!(placeholders, vec!["{}", "{:?}", "{1:0$}"]);
     }

src/lib.rs

@@ -182,9 +182,6 @@
 //! [`Constructor`]: https://jeltef.github.io/derive_more/derive_more/constructor.html
 //! [`IsVariant`]: https://jeltef.github.io/derive_more/derive_more/is_variant.html
 
-// Suppress Clippy tips to use `matches!` macro, because minimal supported Rust version is 1.36.0.
-// Remove this suppression once minimal supported Rust version is bumped up to 1.42.0 or above.
-#![cfg_attr(nightly, allow(clippy::match_like_matches_macro))]
 #![recursion_limit = "128"]
 
 extern crate proc_macro;