From 0ec852fe743144803a400cc9e7310622415e0641 Mon Sep 17 00:00:00 2001
From: mcmah309 <dillonmcmahon79@gmail.com>
Date: Thu, 17 Oct 2024 17:47:31 +0000
Subject: [PATCH] feat: Support not specifying source for display format str

---
 README.md          |  1 +
 impl/Cargo.toml    |  1 +
 impl/src/expand.rs | 30 ++++++++++++++++++++++++++----
 tests/mod.rs       | 28 ++++++++++++++++++++++++++--
 4 files changed, 54 insertions(+), 6 deletions(-)

diff --git a/README.md b/README.md
index 494318a..33f3f89 100644
--- a/README.md
+++ b/README.md
@@ -401,6 +401,7 @@ error_set! {
         InvalidCredentials
     };
     LoginError = {
+        #[display("Io Error: {}")] // equivalent to `#[display("Io Error: {}", source)]`
         IoError(std::io::Error),
     } || AuthError;
 }
diff --git a/impl/Cargo.toml b/impl/Cargo.toml
index ee4f669..52e01df 100644
--- a/impl/Cargo.toml
+++ b/impl/Cargo.toml
@@ -15,6 +15,7 @@ syn = { version = "2", default-features = false, features = ["parsing","derive",
 proc-macro2 = "1"
 quote = "1"
 indices = "0.3"
+dyn-fmt = "0.4.3"
 
 [features]
 default = []
diff --git a/impl/src/expand.rs b/impl/src/expand.rs
index 79c8484..f2a5abc 100644
--- a/impl/src/expand.rs
+++ b/impl/src/expand.rs
@@ -166,11 +166,20 @@ fn impl_display(error_enum_node: &ErrorEnumGraphNode, token_stream: &mut TokenSt
                 let name = &variant.name;
                 if let Some(display) = &variant.display {
                     let tokens = &display.tokens;
-                    if is_str_literal(tokens.clone()) {
-                        error_variant_tokens.append_all(quote::quote! {
-                            #enum_name::#name(ref source) =>  #tokens,
-                        });
+                    if let Some(string) = extract_string_from_str_literal(tokens.clone()) {
+                        // e.g. `"{}"`
+                        if is_format_str(&string) {
+                            error_variant_tokens.append_all(quote::quote! {
+                                #enum_name::#name(ref source) =>  &*format!(#tokens, source),
+                            });
+                        } else {
+                            // e.g. `"literal str"`
+                            error_variant_tokens.append_all(quote::quote! {
+                                #enum_name::#name(_) =>  #tokens,
+                            });
+                        }
                     } else {
+                        // e.g. `"field: {}", source.field`
                         error_variant_tokens.append_all(quote::quote! {
                             #enum_name::#name(ref source) =>  &*format!(#tokens),
                         });
@@ -383,6 +392,19 @@ fn is_str_literal(input: TokenStream) -> bool {
     false
 }
 
+fn extract_string_from_str_literal(input: TokenStream) -> Option<String> {
+    if let Ok(expr) = syn::parse2::<Lit>(input) {
+        if let Lit::Str(lit) = expr {
+            return Some(lit.value());
+        }
+    }
+    None
+}
+
+fn is_format_str(str: &str) -> bool {
+    dyn_fmt::AsStrFormatExt::format(&str, ["t"]) != str
+}
+
 //************************************************************************//
 
 #[cfg(feature = "coerce_macro")]
diff --git a/tests/mod.rs b/tests/mod.rs
index 8c636ce..f7381d9 100644
--- a/tests/mod.rs
+++ b/tests/mod.rs
@@ -405,6 +405,14 @@ pub mod display_ref_error {
             #[display("Y io error: {}", source)]
             IoError(std::io::Error),
         };
+        Y2 = {
+            #[display("Y2 io error type: {}", source.kind())]
+            IoError(std::io::Error),
+        };
+        Z = {
+            #[display("Z io error: {}")]
+            IoError(std::io::Error),
+        };
     }
 
     #[test]
@@ -413,19 +421,35 @@ pub mod display_ref_error {
             std::io::ErrorKind::OutOfMemory,
             "oops out of memory 1",
         ));
-
         assert_eq!(x.to_string(), "X io error".to_string());
 
         let y = Y::IoError(std::io::Error::new(
             std::io::ErrorKind::OutOfMemory,
             "oops out of memory 2",
         ));
-
         assert_eq!(y.to_string(), "Y io error: oops out of memory 2".to_string());
+
+        let y2 = Y2::IoError(std::io::Error::new(
+            std::io::ErrorKind::OutOfMemory,
+            "oops out of memory 3",
+        ));
+        assert_eq!(y2.to_string(), "Y2 io error type: out of memory".to_string());
+
+        let z = Z::IoError(std::io::Error::new(
+            std::io::ErrorKind::OutOfMemory,
+            "oops out of memory 4",
+        ));
+        assert_eq!(z.to_string(), "Z io error: oops out of memory 4".to_string());
+
         let y_to_x: X = y.into();
         let x_to_y: Y = x.into();
         assert_eq!(y_to_x.to_string(), "X io error".to_string());
         assert_eq!(x_to_y.to_string(), "Y io error: oops out of memory 1".to_string());
+
+        let z_to_y2: Y2 = z.into();
+        let y2_to_z: Z = y2.into();
+        assert_eq!(z_to_y2.to_string(), "Y2 io error type: out of memory".to_string());
+        assert_eq!(y2_to_z.to_string(), "Z io error: oops out of memory 3".to_string());
     }
 }