strum_macros/macros/strings/
display.rs

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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(ref unnamed_fields) => {
33                // Transform unnamed params '(String, u8)' to '(ref field0, ref field1)'
34                let names: Punctuated<_, Token!(,)> = unnamed_fields
35                    .unnamed
36                    .iter()
37                    .enumerate()
38                    .map(|(index, field)| {
39                        assert!(field.ident.is_none());
40                        let ident = syn::parse_str::<Ident>(format!("field{}", index).as_str()).unwrap();
41                        quote! { ref #ident }
42                    })
43                    .collect();
44                quote! { (#names) }
45            }
46            Fields::Named(ref field_names) => {
47                // Transform named params '{ name: String, age: u8 }' to '{ ref name, ref age }'
48                let names: Punctuated<TokenStream, Token!(,)> = field_names
49                    .named
50                    .iter()
51                    .map(|field| {
52                        let ident = field.ident.as_ref().unwrap();
53                        quote! { ref #ident }
54                    })
55                    .collect();
56
57                quote! { {#names} }
58            }
59        };
60
61        if variant_properties.to_string.is_none() && variant_properties.default.is_some() {
62            match &variant.fields {
63                Fields::Unnamed(fields) if fields.unnamed.len() == 1 => {
64                    arms.push(quote! { #name::#ident(ref s) => ::core::fmt::Display::fmt(s, f) });
65                }
66                _ => {
67                    return Err(syn::Error::new_spanned(
68                        variant,
69                        "Default only works on newtype structs with a single String field",
70                    ))
71                }
72            }
73        } else {
74            let arm = match variant.fields {
75                Fields::Named(ref field_names) => {
76                    let used_vars = capture_format_string_idents(&output)?;
77                    if used_vars.is_empty() {
78                        quote! { #name::#ident #params => ::core::fmt::Display::fmt(#output, f) }
79                    } else {
80                        // Create args like 'name = name, age = age' for format macro
81                        let args: Punctuated<_, Token!(,)> = field_names
82                            .named
83                            .iter()
84                            .filter_map(|field| {
85                                let ident = field.ident.as_ref().unwrap();
86                                // Only contain variables that are used in format string
87                                if !used_vars.contains(ident) {
88                                    None
89                                } else {
90                                    Some(quote! { #ident = #ident })
91                                }
92                            })
93                            .collect();
94
95                        quote! {
96                            #[allow(unused_variables)]
97                            #name::#ident #params => ::core::fmt::Display::fmt(&format!(#output, #args), f)
98                        }
99                    }
100                },
101                Fields::Unnamed(ref unnamed_fields) => {
102                    let used_vars = capture_format_strings(&output)?;
103                    if used_vars.iter().any(String::is_empty) {
104                        return Err(syn::Error::new_spanned(
105                            &output,
106                            "Empty {} is not allowed; Use manual numbering ({0})",
107                        ))
108                    }
109                    if used_vars.is_empty() {
110                        quote! { #name::#ident #params => ::core::fmt::Display::fmt(#output, f) }
111                    } else {
112                        let args: Punctuated<_, Token!(,)> = unnamed_fields
113                            .unnamed
114                            .iter()
115                            .enumerate()
116                            .map(|(index, field)| {
117                                assert!(field.ident.is_none());
118                                syn::parse_str::<Ident>(format!("field{}", index).as_str()).unwrap()
119                            })
120                            .collect();
121                        quote! {
122                            #[allow(unused_variables)]
123                            #name::#ident #params => ::core::fmt::Display::fmt(&format!(#output, #args), f)
124                        }
125                    }
126                }
127                Fields::Unit => {
128                    let used_vars = capture_format_strings(&output)?;
129                    if !used_vars.is_empty() {
130                        return Err(syn::Error::new_spanned(
131                            &output,
132                            "Unit variants do not support interpolation",
133                        ));
134                    }
135
136                    quote! { #name::#ident #params => ::core::fmt::Display::fmt(#output, f) }
137                }
138            };
139
140            arms.push(arm);
141        }
142    }
143
144    if arms.len() < variants.len() {
145        arms.push(quote! { _ => panic!("fmt() called on disabled variant.") });
146    }
147
148    Ok(quote! {
149        impl #impl_generics ::core::fmt::Display for #name #ty_generics #where_clause {
150            fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::result::Result<(), ::core::fmt::Error> {
151                match *self {
152                    #(#arms),*
153                }
154            }
155        }
156    })
157}
158
159fn capture_format_string_idents(string_literal: &LitStr) -> syn::Result<Vec<Ident>> {
160    capture_format_strings(string_literal)?.into_iter().map(|ident| {
161        syn::parse_str::<Ident>(ident.as_str()).map_err(|_| {
162            syn::Error::new_spanned(
163                string_literal,
164                "Invalid identifier inside format string bracket",
165            )
166        })
167    }).collect()
168}
169
170fn capture_format_strings(string_literal: &LitStr) -> syn::Result<Vec<String>> {
171    // Remove escaped brackets
172    let format_str = string_literal.value().replace("{{", "").replace("}}", "");
173
174    let mut new_var_start_index: Option<usize> = None;
175    let mut var_used = Vec::new();
176
177    for (i, chr) in format_str.bytes().enumerate() {
178        if chr == b'{' {
179            if new_var_start_index.is_some() {
180                return Err(syn::Error::new_spanned(
181                    string_literal,
182                    "Bracket opened without closing previous bracket",
183                ));
184            }
185            new_var_start_index = Some(i);
186            continue;
187        }
188
189        if chr == b'}' {
190            let start_index = new_var_start_index.take().ok_or(syn::Error::new_spanned(
191                string_literal,
192                "Bracket closed without previous opened bracket",
193            ))?;
194
195            let inside_brackets = &format_str[start_index + 1..i];
196            let ident_str = inside_brackets.split(":").next().unwrap().trim_end();
197            var_used.push(ident_str.to_owned());
198        }
199    }
200
201    Ok(var_used)
202}
strum_macros/macros/strings/display.rs

strum_macros/macros/strings/
display.rs
