Merge pull request #6 from yaahc/displaypath

feat: add Display support for Path and PathBuf

Author: yaahc

.github/workflows/ci.yml

@@ -39,6 +39,10 @@ jobs:
       - uses: actions-rs/cargo@v1
         with:
           command: test
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --no-default-features
 
   fmt:
     name: Rustfmt

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "displaydoc"
-version = "0.1.4"
+version = "0.1.5"
 authors = ["Jane Lusby <jlusby@yaah.dev>"]
 edition = "2018"
 license = "MIT OR Apache-2.0"
@@ -16,7 +16,9 @@ A derive macro for implementing the display Trait via a doc comment and string i
 [lib]
 proc-macro = true
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+[features]
+default = ["std"]
+std = []
 
 [dependencies]
 syn = "1.0"
@@ -28,3 +30,4 @@ trybuild = "1.0"
 static_assertions = "0.3.4"
 libc = { version = "0.2", default-features = false }
 rustversion = "1.0.0"
+pretty_assertions = "0.6.1"

README.md

@@ -11,7 +11,7 @@ This library provides a convenient derive macro for the standard library's
 
 ```toml
 [dependencies]
-displaydoc = "0.1.4"
+displaydoc = "0.1"
 ```
 
 *Compiler support: requires rustc 1.31+*
@@ -62,6 +62,9 @@ pub enum DataStoreError {
 1. **Is this crate `no_std` compatible?**
     * Yes! This crate implements the `core::fmt::Display` trait not the `std::fmt::Display` trait so it should work in `std` and `no_std` environments.
 
+2. **Does this crate work with `Path` and `PathBuf` via the `Display` trait?**
+    * Yuuup. This crate uses @dtolnay's [autoref specialization technique](https://github.com/dtolnay/case-studies/blob/master/autoref-specialization/README.md) to add a special trait for types to get the display impl, it then specializes for `Path` and `PathBuf` and when either of these types are found it calls `self.display()` to get a `std::path::Display<'_>` type which can be used with the Display format specifier!
+
 <br>
 
 #### License

src/expand.rs

@@ -11,6 +11,42 @@ pub fn derive(input: &DeriveInput) -> Result<TokenStream> {
     }
 }
 
+#[cfg(feature = "std")]
+fn specialization() -> TokenStream {
+    quote! {
+        trait DisplayToDisplayDoc {
+            fn get_display(&self) -> Self;
+        }
+
+        impl<T: core::fmt::Display> DisplayToDisplayDoc for &T {
+            fn get_display(&self) -> Self {
+                self
+            }
+        }
+
+        trait PathToDisplayDoc {
+            fn get_display(&self) -> std::path::Display<'_>;
+        }
+
+        impl PathToDisplayDoc for std::path::Path {
+            fn get_display(&self) -> std::path::Display<'_> {
+                self.display()
+            }
+        }
+
+        impl PathToDisplayDoc for std::path::PathBuf {
+            fn get_display(&self) -> std::path::Display<'_> {
+                self.display()
+            }
+        }
+    }
+}
+
+#[cfg(not(feature = "std"))]
+fn specialization() -> TokenStream {
+    quote! {}
+}
+
 fn impl_struct(input: &DeriveInput, data: &DataStruct) -> Result<TokenStream> {
     let ty = &input.ident;
     let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
@@ -38,7 +74,11 @@ fn impl_struct(input: &DeriveInput, data: &DataStruct) -> Result<TokenStream> {
         }
     });
 
+    let needed_traits = specialization();
+
     Ok(quote! {
+        #needed_traits
+
         #display
     })
 }
@@ -89,7 +129,11 @@ fn impl_enum(input: &DeriveInput, data: &DataEnum) -> Result<TokenStream> {
         return Err(Error::new_spanned(input, "Missing doc comments"));
     };
 
+    let needed_traits = specialization();
+
     Ok(quote! {
+        #needed_traits
+
         #display
     })
 }

src/fmt.rs

@@ -3,6 +3,20 @@ use proc_macro2::TokenStream;
 use quote::quote_spanned;
 use syn::{Ident, LitStr};
 
+#[cfg(feature = "std")]
+const IS_STD: bool = true;
+#[cfg(not(feature = "std"))]
+const IS_STD: bool = false;
+
+macro_rules! peek_next {
+    ($read:ident) => {
+        match $read.chars().next() {
+            Some(next) => next,
+            None => return,
+        }
+    };
+}
+
 impl Display {
     // Transform `"error {var}"` to `"error {}", var`.
     pub fn expand_shorthand(&mut self) {
@@ -15,22 +29,33 @@ impl Display {
         while let Some(brace) = read.find('{') {
             out += &read[..=brace];
             read = &read[brace + 1..];
+
+            // skip cases where we find a {{
             if read.starts_with('{') {
                 out.push('{');
                 read = &read[1..];
                 continue;
             }
-            let next = match read.chars().next() {
-                Some(next) => next,
-                None => return,
-            };
+
+            let next = peek_next!(read);
+
             let var = match next {
                 '0'..='9' => take_int(&mut read),
                 'a'..='z' | 'A'..='Z' | '_' => take_ident(&mut read),
                 _ => return,
             };
+
             let ident = Ident::new(&var, span);
-            args.extend(quote_spanned!(span=> , #ident));
+
+            let next = peek_next!(read);
+
+            let arg = if IS_STD && next == '}' {
+                quote_spanned!(span=> , (&#ident).get_display())
+            } else {
+                quote_spanned!(span=> , #ident)
+            };
+
+            args.extend(arg);
         }
 
         out += read;
@@ -71,6 +96,7 @@ fn take_ident(read: &mut &str) -> String {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use pretty_assertions::assert_eq;
     use proc_macro2::Span;
 
     fn assert(input: &str, fmt: &str, args: &str) {
@@ -85,12 +111,20 @@ mod tests {
 
     #[test]
     fn test_expand() {
-        assert("error {var}", "error {}", ", var");
         assert("fn main() {{ }}", "fn main() {{ }}", "");
+    }
+
+    #[test]
+    #[cfg_attr(not(feature = "std"), ignore)]
+    fn test_std_expand() {
         assert(
             "{v} {v:?} {0} {0:?}",
             "{} {:?} {} {:?}",
-            ", v , v , _0 , _0",
+            ", ( & v ) . get_display ( ) , v , ( & _0 ) . get_display ( ) , _0",
         );
+        assert("error {var}", "error {}", ", ( & var ) . get_display ( )");
+
+        // assert("The path {0.display()}", "The path {}", "0.display()");
+        // assert("The path {0.display():?}", "The path {:?}", "0.display()");
     }
 }

tests/compile_tests.rs

@@ -1,4 +1,6 @@
+#[allow(unused_attributes)]
 #[rustversion::attr(not(nightly), ignore)]
+#[cfg_attr(feature = "std", ignore)]
 #[test]
 fn no_std() {
     let t = trybuild::TestCases::new();

tests/happy.rs

@@ -1,4 +1,5 @@
 use displaydoc::Display;
+// use std::path::PathBuf;
 
 #[derive(Display)]
 enum Happy {
@@ -17,6 +18,8 @@ enum Happy {
     /// Variant5 just has {0} many problems
     /// but multi line comments aren't one of them
     Variant5(u32),
+    // /// The path {0.display()}
+    // Variant6(PathBuf),
 }
 
 fn assert_display<T: std::fmt::Display>(input: T, expected: &'static str) {
@@ -34,4 +37,8 @@ fn does_it_print() {
         "Variant4 wants to have a lot of lines\n\n Lets see how this works out for it",
     );
     assert_display(Happy::Variant5(2), "Variant5 just has 2 many problems");
+    // assert_display(
+    //     Happy::Variant6(PathBuf::from("/var/log/happy")),
+    //     "The path /var/log/happy",
+    // );
 }