strum_macros/macros/strings/
display.rs

1use proc_macro2::{Ident, TokenStream};
2use quote::quote;
3use syn::{punctuated::Punctuated, Data, DeriveInput, Fields, LitStr, Token};
4
5use crate::helpers::{
6    non_enum_error, non_single_field_variant_error, HasStrumVariantProperties, HasTypeProperties,
7};
8
9pub fn display_inner(ast: &DeriveInput) -> syn::Result<TokenStream> {
10    let name = &ast.ident;
11    let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
12    let variants = match &ast.data {
13        Data::Enum(v) => &v.variants,
14        _ => return Err(non_enum_error()),
15    };
16
17    let type_properties = ast.get_type_properties()?;
18
19    let mut arms = Vec::new();
20    for variant in variants {
21        let ident = &variant.ident;
22        let variant_properties = variant.get_variant_properties()?;
23
24        if variant_properties.disabled.is_some() {
25            continue;
26        }
27
28        if let Some(..) = variant_properties.transparent {
29            let arm = super::extract_single_field_variant_and_then(name, variant, |tok| {
30                quote! { ::core::fmt::Display::fmt(#tok, f) }
31            })
32            .map_err(|_| non_single_field_variant_error("transparent"))?;
33
34            arms.push(arm);
35            continue;
36        }
37
38        // Look at all the serialize attributes.
39        let output = variant_properties
40            .get_preferred_name(type_properties.case_style, type_properties.prefix.as_ref());
41
42        let params = match variant.fields {
43            Fields::Unit => quote! {},
44            Fields::Unnamed(ref unnamed_fields) => {
45                // Transform unnamed params '(String, u8)' to '(ref field0, ref field1)'
46                let names: Punctuated<_, Token!(,)> = unnamed_fields
47                    .unnamed
48                    .iter()
49                    .enumerate()
50                    .map(|(index, field)| {
51                        assert!(field.ident.is_none());
52                        let ident =
53                            syn::parse_str::<Ident>(format!("field{}", index).as_str()).unwrap();
54                        quote! { ref #ident }
55                    })
56                    .collect();
57                quote! { (#names) }
58            }
59            Fields::Named(ref field_names) => {
60                // Transform named params '{ name: String, age: u8 }' to '{ ref name, ref age }'
61                let names: Punctuated<TokenStream, Token!(,)> = field_names
62                    .named
63                    .iter()
64                    .map(|field| {
65                        let ident = field.ident.as_ref().unwrap();
66                        quote! { ref #ident }
67                    })
68                    .collect();
69
70                quote! { {#names} }
71            }
72        };
73
74        if variant_properties.to_string.is_none() && variant_properties.default.is_some() {
75            let arm = super::extract_single_field_variant_and_then(name, variant, |tok| {
76                quote! { ::core::fmt::Display::fmt(#tok, f)}
77            })
78            .map_err(|_| {
79                syn::Error::new_spanned(
80                    variant,
81                    "Default only works on newtype structs with a single String field",
82                )
83            })?;
84
85            arms.push(arm);
86            continue;
87        }
88
89        let arm = match variant.fields {
90            Fields::Named(ref field_names) => {
91                let used_vars = capture_format_string_idents(&output)?;
92                if used_vars.is_empty() {
93                    quote! { #name::#ident #params => ::core::fmt::Display::fmt(#output, f) }
94                } else {
95                    // Create args like 'name = name, age = age' for format macro
96                    let args: Punctuated<_, Token!(,)> = field_names
97                        .named
98                        .iter()
99                        .filter_map(|field| {
100                            let ident = field.ident.as_ref().unwrap();
101                            // Only contain variables that are used in format string
102                            if !used_vars.contains(ident) {
103                                None
104                            } else {
105                                Some(quote! { #ident = #ident })
106                            }
107                        })
108                        .collect();
109
110                    quote! {
111                        #[allow(unused_variables)]
112                        #name::#ident #params => ::core::fmt::Display::fmt(&format_args!(#output, #args), f)
113                    }
114                }
115            }
116            Fields::Unnamed(ref unnamed_fields) => {
117                let used_vars = capture_format_strings(&output)?;
118                if used_vars.iter().any(String::is_empty) {
119                    return Err(syn::Error::new_spanned(
120                        &output,
121                        "Empty {} is not allowed; Use manual numbering ({0})",
122                    ));
123                }
124                if used_vars.is_empty() {
125                    quote! { #name::#ident #params => ::core::fmt::Display::fmt(#output, f) }
126                } else {
127                    let args: Punctuated<_, Token!(,)> = unnamed_fields
128                        .unnamed
129                        .iter()
130                        .enumerate()
131                        .map(|(index, field)| {
132                            assert!(field.ident.is_none());
133                            syn::parse_str::<Ident>(format!("field{}", index).as_str()).unwrap()
134                        })
135                        .collect();
136                    quote! {
137                        #[allow(unused_variables)]
138                        #name::#ident #params => ::core::fmt::Display::fmt(&format!(#output, #args), f)
139                    }
140                }
141            }
142            Fields::Unit => {
143                let used_vars = capture_format_strings(&output)?;
144                if !used_vars.is_empty() {
145                    return Err(syn::Error::new_spanned(
146                        &output,
147                        "Unit variants do not support interpolation",
148                    ));
149                }
150
151                quote! { #name::#ident #params => ::core::fmt::Display::fmt(#output, f) }
152            }
153        };
154
155        arms.push(arm);
156    }
157
158    if arms.len() < variants.len() {
159        arms.push(quote! { _ => panic!("fmt() called on disabled variant.") });
160    }
161
162    Ok(quote! {
163        impl #impl_generics ::core::fmt::Display for #name #ty_generics #where_clause {
164            fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::result::Result<(), ::core::fmt::Error> {
165                match *self {
166                    #(#arms),*
167                }
168            }
169        }
170    })
171}
172
173fn capture_format_string_idents(string_literal: &LitStr) -> syn::Result<Vec<Ident>> {
174    capture_format_strings(string_literal)?
175        .into_iter()
176        .map(|ident| {
177            syn::parse_str::<Ident>(ident.as_str()).map_err(|_| {
178                syn::Error::new_spanned(
179                    string_literal,
180                    "Invalid identifier inside format string bracket",
181                )
182            })
183        })
184        .collect()
185}
186
187fn capture_format_strings(string_literal: &LitStr) -> syn::Result<Vec<String>> {
188    // Remove escaped brackets
189    let format_str = string_literal.value().replace("{{", "").replace("}}", "");
190
191    let mut new_var_start_index: Option<usize> = None;
192    let mut var_used = Vec::new();
193
194    for (i, chr) in format_str.bytes().enumerate() {
195        if chr == b'{' {
196            if new_var_start_index.is_some() {
197                return Err(syn::Error::new_spanned(
198                    string_literal,
199                    "Bracket opened without closing previous bracket",
200                ));
201            }
202            new_var_start_index = Some(i);
203            continue;
204        }
205
206        if chr == b'}' {
207            let start_index = new_var_start_index.take().ok_or(syn::Error::new_spanned(
208                string_literal,
209                "Bracket closed without previous opened bracket",
210            ))?;
211
212            let inside_brackets = &format_str[start_index + 1..i];
213            let ident_str = inside_brackets.split(":").next().unwrap().trim_end();
214            var_used.push(ident_str.to_owned());
215        }
216    }
217
218    Ok(var_used)
219}
strum_macros/macros/strings/display.rs

strum_macros/macros/strings/
display.rs
