implement Display for enums with attribute config_type (#3621)

config_proc_macro/src/item_enum.rs

@@ -23,6 +23,7 @@ pub fn define_config_type_on_enum(em: &syn::ItemEnum) -> syn::Result<TokenStream
 
     let impl_doc_hint = impl_doc_hint(&em.ident, &em.variants);
     let impl_from_str = impl_from_str(&em.ident, &em.variants);
+    let impl_display = impl_display(&em.ident, &em.variants);
     let impl_serde = impl_serde(&em.ident, &em.variants);
     let impl_deserialize = impl_deserialize(&em.ident, &em.variants);
 
@@ -31,6 +32,7 @@ pub fn define_config_type_on_enum(em: &syn::ItemEnum) -> syn::Result<TokenStream
         mod #mod_name {
             #[derive(Debug, Copy, Clone, Eq, PartialEq)]
             pub #enum_token #ident #generics { #variants }
+            #impl_display
             #impl_doc_hint
             #impl_from_str
             #impl_serde
@@ -68,6 +70,29 @@ fn impl_doc_hint(ident: &syn::Ident, variants: &Variants) -> TokenStream {
     }
 }
 
+fn impl_display(ident: &syn::Ident, variants: &Variants) -> TokenStream {
+    let vs = variants
+        .iter()
+        .filter(|v| is_unit(v))
+        .map(|v| (config_value_of_variant(v), &v.ident));
+    let match_patterns = fold_quote(vs, |(s, v)| {
+        quote! {
+            #ident::#v => write!(f, "{}", #s),
+        }
+    });
+    quote! {
+        use std::fmt;
+        impl fmt::Display for #ident {
+            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                match self {
+                    #match_patterns
+                    _ => unimplemented!(),
+                }
+            }
+        }
+    }
+}
+
 fn impl_from_str(ident: &syn::Ident, variants: &Variants) -> TokenStream {
     let vs = variants
         .iter()

src/config/config_type.rs

@@ -249,11 +249,15 @@ macro_rules! create_config {
                             }
                             name_out.push_str(name_raw);
                             name_out.push(' ');
+                            let mut default_str = format!("{}", $def);
+                            if default_str.is_empty() {
+                                default_str = String::from("\"\"");
+                            }
                             writeln!(out,
-                                    "{}{} Default: {:?}{}",
+                                    "{}{} Default: {}{}",
                                     name_out,
                                     <$ty>::doc_hint(),
-                                    $def,
+                                    default_str,
                                     if !$stb { " (unstable)" } else { "" }).unwrap();
                             $(
                                 writeln!(out, "{}{}", space_str, $dstring).unwrap();

src/config/file_lines.rs

@@ -1,5 +1,6 @@
 //! This module contains types and functions to support formatting specific line ranges.
 
+use itertools::Itertools;
 use std::collections::HashMap;
 use std::path::PathBuf;
 use std::rc::Rc;
@@ -92,6 +93,12 @@ impl<'a> From<&'a LineRange> for Range {
     }
 }
 
+impl fmt::Display for Range {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}..{}", self.lo, self.hi)
+    }
+}
+
 impl Range {
     pub fn new(lo: usize, hi: usize) -> Range {
         Range { lo, hi }
@@ -149,6 +156,21 @@ impl Range {
 #[derive(Clone, Debug, Default, PartialEq)]
 pub struct FileLines(Option<HashMap<FileName, Vec<Range>>>);
 
+impl fmt::Display for FileLines {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match &self.0 {
+            None => write!(f, "None")?,
+            Some(map) => {
+                for (file_name, ranges) in map.iter() {
+                    write!(f, "{}: ", file_name)?;
+                    write!(f, "{}\n", ranges.iter().format(", "))?;
+                }
+            }
+        };
+        Ok(())
+    }
+}
+
 /// Normalizes the ranges so that the invariants for `FileLines` hold: ranges are non-overlapping,
 /// and ordered by their start point.
 fn normalize_ranges(ranges: &mut HashMap<FileName, Vec<Range>>) {

src/config/options.rs

@@ -3,6 +3,7 @@ use std::fmt;
 use std::path::{Path, PathBuf};
 
 use atty;
+use itertools::Itertools;
 use rustfmt_config_proc_macro::config_type;
 use serde::de::{SeqAccess, Visitor};
 use serde::ser::SerializeSeq;
@@ -193,6 +194,12 @@ pub struct WidthHeuristics {
     pub single_line_if_else_max_width: usize,
 }
 
+impl fmt::Display for WidthHeuristics {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:?}", self)
+    }
+}
+
 impl WidthHeuristics {
     // Using this WidthHeuristics means we ignore heuristics.
     pub fn null() -> WidthHeuristics {
@@ -264,6 +271,21 @@ pub struct IgnoreList {
     rustfmt_toml_path: PathBuf,
 }
 
+impl fmt::Display for IgnoreList {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            f,
+            "[{}]",
+            self.path_set
+                .iter()
+                .format_with(", ", |path, f| f(&format_args!(
+                    "{}",
+                    path.to_string_lossy()
+                )))
+        )
+    }
+}
+
 impl Serialize for IgnoreList {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where