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

pretty_name/
type_name.rs
