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

pretty_name/
type_name.rs
