pretty_name/
type_name.rs

1use syn::*;
2
3/// Get the human-friendly type name of given type `T`, removing visual clutter such as
4/// full module paths.
5/// 
6/// # Examples
7/// ```rust
8/// use pretty_name::type_name;
9/// assert_eq!(type_name::<Option<i32>>(), "Option<i32>");
10/// assert_eq!(type_name::<&str>(), "&str");
11/// assert_eq!(type_name::<Vec<Box<dyn std::fmt::Debug>>>(), "Vec<Box<dyn Debug>>");
12/// ```
13pub fn type_name<T: ?Sized>() -> &'static str {
14    use std::cell::RefCell;
15    use std::collections::HashMap;
16    use std::collections::hash_map::Entry;
17
18    thread_local! {
19        static TYPE_NAME_CACHE: RefCell<HashMap<&'static str, &'static str>> =
20            RefCell::new(HashMap::new());
21    }
22
23    let full_name = std::any::type_name::<T>();
24    TYPE_NAME_CACHE.with_borrow_mut(|cache| match cache.entry(full_name) {
25        Entry::Occupied(entry) =>
26            *entry.get(),
27        Entry::Vacant(entry) =>
28            *entry.insert(type_name_internal::<T>()),
29    })
30}
31
32/// Get the human-friendly type name of the given value, removing visual clutter such as
33/// full module paths.
34/// 
35/// Note that even if the value is a reference, you should pass a reference to it to get
36/// the correct type name.
37/// 
38/// # Examples
39/// ```rust
40/// use pretty_name::type_name_of_val;
41/// let value = vec![1, 2, 3];
42/// assert_eq!(type_name_of_val(&value), "Vec<i32>");
43/// assert_eq!(type_name_of_val(&value.as_slice()), "&[i32]");
44/// ```
45pub fn type_name_of_val<T: ?Sized>(_: &T) -> &'static str {
46    type_name::<T>()
47}
48
49fn type_name_internal<T: ?Sized>() -> &'static str {
50    let type_name = std::any::type_name::<T>();
51    let Ok(mut ty) = syn::parse_str::<Type>(type_name) else {
52        return "<error>";
53    };
54
55    truncate_type(&mut ty);
56
57    // Use rustfmt to get a nicely formatted type string.
58    // rustfmt only accepts full source files, so we wrap the type in a dummy function.
59    use quote::quote;
60    use rust_format::Formatter as _;
61    let format_result =
62        rust_format::RustFmt::default()
63            .format_tokens(quote!(fn main() -> #ty {}))
64            .unwrap_or("<error>".to_string());
65    let start = const { "fn main() -> ".len() };
66    let end = format_result.len() - const { " {}\r\n".len() };
67    Box::leak(
68        format_result[start..end]
69            .to_owned()
70            .into_boxed_str())
71}
72
73fn truncate_type(ty: &mut Type) {
74    match *ty {
75        Type::Infer(_) |
76        Type::Macro(_) |
77        Type::Never(_) |
78        Type::Verbatim(_) => {}
79
80        Type::Array(TypeArray { ref mut elem, .. }) |
81        Type::Group(TypeGroup { group_token: _, ref mut elem }) |
82        Type::Paren(TypeParen { paren_token: _, ref mut elem }) |
83        Type::Ptr(TypePtr { ref mut elem, .. }) |
84        Type::Slice(TypeSlice { ref mut elem, .. }) => truncate_type(elem),
85
86        Type::Reference(TypeReference {
87            ref mut lifetime,
88            ref mut elem,
89            ..
90        }) => {
91            *lifetime = None;
92            truncate_type(elem);
93        }
94
95        Type::Path(ref mut ty) => truncate_path(&mut ty.path),
96
97        Type::BareFn(ref mut ty) => {
98            for input in ty.inputs.iter_mut() {
99                truncate_type(&mut input.ty);
100            }
101
102            if let ReturnType::Type(_, ref mut ty) = ty.output {
103                truncate_type(ty.as_mut());
104            }
105        }
106
107        Type::ImplTrait(ref mut ty) => {
108            for bound in ty.bounds.iter_mut() {
109                if let &mut TypeParamBound::Trait(ref mut trt) = bound {
110                    truncate_path(&mut trt.path);
111                }
112            }
113        }
114
115        Type::TraitObject(ref mut ty) => {
116            for bound in ty.bounds.iter_mut() {
117                if let &mut TypeParamBound::Trait(ref mut trt) = bound {
118                    truncate_path(&mut trt.path);
119                }
120            }
121        }
122
123        Type::Tuple(ref mut ty) => {
124            for elem in ty.elems.iter_mut() {
125                truncate_type(elem);
126            }
127        }
128
129        _ => { /* non_exhaustive variants */ }
130    }
131}
132
133fn truncate_path(path: &mut Path) {
134    let path_mut = path;
135    let path = std::mem::replace(
136        path_mut,
137        Path {
138            leading_colon: None,
139            segments: Default::default(),
140        });
141
142    let Some(mut last_segment) = path.segments.into_iter().last() else {
143        path_mut.leading_colon = None;
144        path_mut.segments = Default::default();
145        return;
146    };
147
148    match last_segment.arguments {
149        PathArguments::None => {}
150        PathArguments::AngleBracketed(ref mut args) => {
151            for arg in args.args.iter_mut() {
152                match *arg {
153                    GenericArgument::Type(ref mut ty) => truncate_type(ty),
154                    GenericArgument::AssocType(ref mut ty) => {
155                        truncate_type(&mut ty.ty)
156                    }
157                    _ => {}
158                }
159            }
160        }
161        PathArguments::Parenthesized(ref mut args) => {
162            for input in args.inputs.iter_mut() {
163                truncate_type(input);
164            }
165            if let ReturnType::Type(_, ref mut output) = args.output {
166                truncate_type(output);
167            }
168        }
169    }
170
171    path_mut.leading_colon = None;
172    path_mut.segments = Some(last_segment).into_iter().collect();
173}
174
175#[cfg(test)]
176mod test {
177    use super::type_name;
178
179    #[test]
180    fn test_type_name() {
181        // ===== Primitives =====
182        assert_eq!(type_name::<i32>(), "i32");
183        assert_eq!(type_name::<bool>(), "bool");
184
185        // ===== Unsized Primitives =====
186        assert_eq!(type_name::<str>(), "str");
187        assert_eq!(type_name::<[i32]>(), "[i32]");
188
189        // ===== References - Immutable =====
190        assert_eq!(type_name::<&i32>(), "&i32");
191        assert_eq!(type_name::<&str>(), "&str");
192        // Lifetime elision - 'static should be removed
193        assert_eq!(type_name::<&'static str>(), "&str");
194        // Multiple levels of indirection
195        assert_eq!(type_name::<&&&str>(), "&&&str");
196        // Reference to unsized slice
197        assert_eq!(type_name::<&[i32]>(), "&[i32]");
198
199        // ===== References - Mutable =====
200        assert_eq!(type_name::<&mut String>(), "&mut String");
201        assert_eq!(type_name::<&mut &str>(), "&mut &str");
202        assert_eq!(type_name::<&mut str>(), "&mut str");
203        assert_eq!(type_name::<&mut [i32]>(), "&mut [i32]");
204
205        // ===== Raw Pointers =====
206        assert_eq!(type_name::<*const i32>(), "*const i32");
207        assert_eq!(type_name::<*mut i32>(), "*mut i32");
208        assert_eq!(type_name::<*const str>(), "*const str");
209        assert_eq!(type_name::<*mut [u8]>(), "*mut [u8]");
210        // Nested raw pointers
211        assert_eq!(type_name::<*const *mut i32>(), "*const *mut i32");
212        // Mixed pointer types
213        assert_eq!(type_name::<*const &str>(), "*const &str");
214        assert_eq!(type_name::<&*const i32>(), "&*const i32");
215
216        // ===== Arrays =====
217        assert_eq!(type_name::<[i32; 5]>(), "[i32; 5]");
218        assert_eq!(type_name::<[bool; 0]>(), "[bool; 0]");
219        assert_eq!(type_name::<&[i32; 3]>(), "&[i32; 3]");
220        assert_eq!(type_name::<&mut [i32; 5]>(), "&mut [i32; 5]");
221        // Nested arrays
222        assert_eq!(type_name::<[[i32; 2]; 3]>(), "[[i32; 2]; 3]");
223        assert_eq!(type_name::<[[[u8; 2]; 3]; 4]>(), "[[[u8; 2]; 3]; 4]");
224        // Array of tuples
225        assert_eq!(type_name::<[(i32, bool); 10]>(), "[(i32, bool); 10]");
226
227        // ===== Tuples =====
228        assert_eq!(type_name::<()>(), "()");
229        assert_eq!(type_name::<(i32,)>(), "(i32,)");
230        assert_eq!(type_name::<(i32, String, bool)>(), "(i32, String, bool)");
231        // Nested tuples
232        assert_eq!(type_name::<(i32, (String, bool))>(), "(i32, (String, bool))");
233        // Tuples with references to unsized
234        assert_eq!(type_name::<(&str, &[u8])>(), "(&str, &[u8])");
235        assert_eq!(type_name::<(&mut String, &i32)>(), "(&mut String, &i32)");
236
237        // ===== Generic Containers =====
238        assert_eq!(type_name::<Option<i32>>(), "Option<i32>");
239        assert_eq!(type_name::<Option<&str>>(), "Option<&str>");
240        assert_eq!(type_name::<Result<i32, String>>(), "Result<i32, String>");
241        assert_eq!(type_name::<Result<(), ()>>(), "Result<(), ()>");
242        assert_eq!(type_name::<Vec<i32>>(), "Vec<i32>");
243        assert_eq!(type_name::<std::collections::HashMap<String, i32>>(), "HashMap<String, i32>");
244        assert_eq!(type_name::<std::collections::BTreeMap<String, i32>>(), "BTreeMap<String, i32>");
245
246        // ===== Function Pointers =====
247        assert_eq!(type_name::<fn()>(), "fn()");
248        assert_eq!(type_name::<fn(i32) -> i32>(), "fn(i32) -> i32");
249        assert_eq!(type_name::<fn(i32, String, bool)>(), "fn(i32, String, bool)");
250        assert_eq!(type_name::<fn(&str) -> String>(), "fn(&str) -> String");
251        assert_eq!(type_name::<fn(&mut i32)>(), "fn(&mut i32)");
252        assert_eq!(type_name::<fn(*const i32) -> *mut i32>(), "fn(*const i32) -> *mut i32");
253        // Function returning function
254        assert_eq!(type_name::<fn() -> fn(i32) -> i32>(), "fn() -> fn(i32) -> i32");
255        assert_eq!(type_name::<fn(fn(i32) -> i32) -> i32>(), "fn(fn(i32) -> i32) -> i32");
256        // Unsafe and extern functions
257        assert_eq!(type_name::<unsafe fn()>(), "unsafe fn()");
258        assert_eq!(type_name::<extern "C" fn(i32) -> i32>(), "extern \"C\" fn(i32) -> i32");
259        assert_eq!(type_name::<unsafe extern "C" fn(i32)>(), "unsafe extern \"C\" fn(i32)");
260
261        // ===== Trait Objects =====
262        assert_eq!(type_name::<Box<dyn std::fmt::Debug>>(), "Box<dyn Debug>");
263        assert_eq!(type_name::<&dyn std::fmt::Display>(), "&dyn Display");
264        assert_eq!(type_name::<&mut dyn std::io::Write>(), "&mut dyn Write");
265        assert_eq!(type_name::<Box<dyn std::fmt::Debug + Send>>(), "Box<dyn Debug + Send>");
266        assert_eq!(type_name::<Box<dyn std::fmt::Debug + Send + Sync>>(), "Box<dyn Debug + Send + Sync>");
267        assert_eq!(type_name::<dyn std::fmt::Debug>(), "dyn Debug");
268        assert_eq!(type_name::<dyn std::fmt::Debug + Send>(), "dyn Debug + Send");
269
270        // ===== Smart Pointers =====
271        assert_eq!(type_name::<Box<i32>>(), "Box<i32>");
272        assert_eq!(type_name::<Box<str>>(), "Box<str>");
273        assert_eq!(type_name::<Box<[i32]>>(), "Box<[i32]>");
274        assert_eq!(type_name::<std::rc::Rc<String>>(), "Rc<String>");
275        assert_eq!(type_name::<std::sync::Arc<String>>(), "Arc<String>");
276        assert_eq!(type_name::<std::cell::RefCell<i32>>(), "RefCell<i32>");
277
278        // ===== Nested Generic Types =====
279        assert_eq!(type_name::<Vec<Vec<String>>>(), "Vec<Vec<String>>");
280        assert_eq!(type_name::<Vec<Vec<Vec<i32>>>>(), "Vec<Vec<Vec<i32>>>");
281        assert_eq!(type_name::<Option<Result<i32, String>>>(), "Option<Result<i32, String>>");
282        assert_eq!(type_name::<Box<Option<Vec<String>>>>(), "Box<Option<Vec<String>>>");
283        assert_eq!(type_name::<Option<Box<dyn std::fmt::Debug>>>(), "Option<Box<dyn Debug>>");
284        assert_eq!(type_name::<Vec<Option<&str>>>(), "Vec<Option<&str>>");
285
286        // ===== Composite Structures =====
287        assert_eq!(type_name::<(Option<i32>, Result<String, ()>)>(), "(Option<i32>, Result<String, ()>)");
288        assert_eq!(type_name::<&[(i32, String)]>(), "&[(i32, String)]");
289        assert_eq!(type_name::<[(Option<i32>, &str); 5]>(), "[(Option<i32>, &str); 5]");
290        assert_eq!(type_name::<std::collections::HashMap<String, Vec<i32>>>(), "HashMap<String, Vec<i32>>");
291        assert_eq!(type_name::<&[Option<Result<i32, String>>]>(), "&[Option<Result<i32, String>>]");
292        // Function pointers in containers
293        assert_eq!(type_name::<Vec<fn(i32) -> i32>>(), "Vec<fn(i32) -> i32>");
294        assert_eq!(type_name::<Option<fn() -> String>>(), "Option<fn() -> String>");
295
296        // ===== Path Simplification =====
297        assert_eq!(type_name::<std::vec::Vec<i32>>(), "Vec<i32>");
298        assert_eq!(type_name::<std::string::String>(), "String");
299        assert_eq!(type_name::<std::boxed::Box<i32>>(), "Box<i32>");
300        // Nested qualified paths
301        assert_eq!(type_name::<Result<Vec<u8>, std::io::Error>>(), "Result<Vec<u8>, Error>");
302        assert_eq!(type_name::<std::collections::HashMap<std::string::String, std::vec::Vec<i32>>>(), "HashMap<String, Vec<i32>>");
303
304        // ===== Extreme Nesting & Combinations =====
305        assert_eq!(type_name::<Vec<Option<Result<Box<dyn std::fmt::Debug>, String>>>>(), "Vec<Option<Result<Box<dyn Debug>, String>>>");
306        assert_eq!(type_name::<&[Option<&[(i32, &str)]>]>(), "&[Option<&[(i32, &str)]>]");
307        assert_eq!(type_name::<fn(Vec<&str>) -> Option<Result<i32, Box<dyn std::error::Error>>>>(), "fn(Vec<&str>) -> Option<Result<i32, Box<dyn Error>>>");
308
309        // ===== Edge Cases =====
310        assert_eq!(type_name::<[(); 5]>(), "[(); 5]");
311        assert_eq!(type_name::<std::marker::PhantomData<i32>>(), "PhantomData<i32>");
312        assert_eq!(type_name::<std::marker::PhantomData<&str>>(), "PhantomData<&str>");
313    }
314}
pretty_name/type_name.rs

pretty_name/
type_name.rs
