1use proc_macro2::{Ident, TokenStream};
2use quote::quote;
3use syn::{punctuated::Punctuated, Data, DeriveInput, Fields, LitStr, Token};
4
5use crate::helpers::{non_enum_error, HasStrumVariantProperties, HasTypeProperties};
6
7pub fn display_inner(ast: &DeriveInput) -> syn::Result<TokenStream> {
8 let name = &ast.ident;
9 let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
10 let variants = match &ast.data {
11 Data::Enum(v) => &v.variants,
12 _ => return Err(non_enum_error()),
13 };
14
15 let type_properties = ast.get_type_properties()?;
16
17 let mut arms = Vec::new();
18 for variant in variants {
19 let ident = &variant.ident;
20 let variant_properties = variant.get_variant_properties()?;
21
22 if variant_properties.disabled.is_some() {
23 continue;
24 }
25
26 // Look at all the serialize attributes.
27 let output = variant_properties
28 .get_preferred_name(type_properties.case_style, type_properties.prefix.as_ref());
29
30 let params = match variant.fields {
31 Fields::Unit => quote! {},
32 Fields::Unnamed(..) => quote! { (..) },
33 Fields::Named(ref field_names) => {
34 // Transform named params '{ name: String, age: u8 }' to '{ ref name, ref age }'
35 let names: Punctuated<TokenStream, Token!(,)> = field_names
36 .named
37 .iter()
38 .map(|field| {
39 let ident = field.ident.as_ref().unwrap();
40 quote! { ref #ident }
41 })
42 .collect();
43
44 quote! { {#names} }
45 }
46 };
47
48 if variant_properties.to_string.is_none() && variant_properties.default.is_some() {
49 match &variant.fields {
50 Fields::Unnamed(fields) if fields.unnamed.len() == 1 => {
51 arms.push(quote! { #name::#ident(ref s) => ::core::fmt::Display::fmt(s, f) });
52 }
53 _ => {
54 return Err(syn::Error::new_spanned(
55 variant,
56 "Default only works on newtype structs with a single String field",
57 ))
58 }
59 }
60 } else {
61 let arm = if let Fields::Named(ref field_names) = variant.fields {
62 let used_vars = capture_format_string_idents(&output)?;
63 if used_vars.is_empty() {
64 quote! { #name::#ident #params => ::core::fmt::Display::fmt(#output, f) }
65 } else {
66 // Create args like 'name = name, age = age' for format macro
67 let args: Punctuated<_, Token!(,)> = field_names
68 .named
69 .iter()
70 .filter_map(|field| {
71 let ident = field.ident.as_ref().unwrap();
72 // Only contain variables that are used in format string
73 if !used_vars.contains(ident) {
74 None
75 } else {
76 Some(quote! { #ident = #ident })
77 }
78 })
79 .collect();
80
81 quote! {
82 #[allow(unused_variables)]
83 #name::#ident #params => ::core::fmt::Display::fmt(&format!(#output, #args), f)
84 }
85 }
86 } else {
87 quote! { #name::#ident #params => ::core::fmt::Display::fmt(#output, f) }
88 };
89
90 arms.push(arm);
91 }
92 }
93
94 if arms.len() < variants.len() {
95 arms.push(quote! { _ => panic!("fmt() called on disabled variant.") });
96 }
97
98 Ok(quote! {
99 impl #impl_generics ::core::fmt::Display for #name #ty_generics #where_clause {
100 fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::result::Result<(), ::core::fmt::Error> {
101 match *self {
102 #(#arms),*
103 }
104 }
105 }
106 })
107}
108
109fn capture_format_string_idents(string_literal: &LitStr) -> syn::Result<Vec<Ident>> {
110 // Remove escaped brackets
111 let format_str = string_literal.value().replace("{{", "").replace("}}", "");
112
113 let mut new_var_start_index: Option<usize> = None;
114 let mut var_used: Vec<Ident> = Vec::new();
115
116 for (i, chr) in format_str.bytes().enumerate() {
117 if chr == b'{' {
118 if new_var_start_index.is_some() {
119 return Err(syn::Error::new_spanned(
120 string_literal,
121 "Bracket opened without closing previous bracket",
122 ));
123 }
124 new_var_start_index = Some(i);
125 continue;
126 }
127
128 if chr == b'}' {
129 let start_index = new_var_start_index.take().ok_or(syn::Error::new_spanned(
130 string_literal,
131 "Bracket closed without previous opened bracket",
132 ))?;
133
134 let inside_brackets = &format_str[start_index + 1..i];
135 let ident_str = inside_brackets.split(":").next().unwrap();
136 let ident = syn::parse_str::<Ident>(ident_str).map_err(|_| {
137 syn::Error::new_spanned(
138 string_literal,
139 "Invalid identifier inside format string bracket",
140 )
141 })?;
142 var_used.push(ident);
143 }
144 }
145
146 Ok(var_used)
147}
148