Split GenerateBacktrace into two traits to allow reuse

snafu-derive/src/shared.rs

@@ -121,11 +121,11 @@ pub mod context_selector {
                 .collect()
         }
 
-        fn construct_backtrace_field(&self) -> Option<TokenStream> {
+        fn construct_implicit_fields(&self) -> Option<TokenStream> {
             self.backtrace_field.map(|field| {
                 let crate_root = self.crate_root;
                 let name = &field.name;
-                quote! { #name: #crate_root::GenerateBacktrace::generate(), }
+                quote! { #name: #crate_root::GenerateImplicitData::generate(), }
             })
         }
 
@@ -165,7 +165,7 @@ pub mod context_selector {
             let visibility = self.visibility;
             let extended_where_clauses = self.extended_where_clauses();
             let transfer_user_fields = self.transfer_user_fields();
-            let construct_backtrace_field = self.construct_backtrace_field();
+            let construct_implicit_fields = self.construct_implicit_fields();
 
             quote! {
                 impl<#(#user_field_generics,)*> #parameterized_selector_name {
@@ -176,7 +176,7 @@ pub mod context_selector {
                         #(#extended_where_clauses),*
                     {
                         #error_constructor_name {
-                            #construct_backtrace_field
+                            #construct_implicit_fields
                             #(#transfer_user_fields,)*
                         }
                     }
@@ -201,7 +201,7 @@ pub mod context_selector {
             let user_field_generics = self.user_field_generics();
             let extended_where_clauses = self.extended_where_clauses();
             let transfer_user_fields = self.transfer_user_fields();
-            let construct_backtrace_field = self.construct_backtrace_field();
+            let construct_implicit_fields = self.construct_implicit_fields();
 
             let (source_ty, transfer_source_field) = match source_field {
                 Some(source_field) => {
@@ -222,7 +222,7 @@ pub mod context_selector {
                     fn into_error(self, error: Self::Source) -> #parameterized_error_name {
                         #error_constructor_name {
                             #transfer_source_field
-                            #construct_backtrace_field
+                            #construct_implicit_fields
                             #(#transfer_user_fields),*
                         }
                     }
@@ -238,7 +238,7 @@ pub mod context_selector {
             let crate_root = self.crate_root;
             let parameterized_error_name = self.parameterized_error_name;
             let error_constructor_name = self.error_constructor_name;
-            let construct_backtrace_field = self.construct_backtrace_field();
+            let construct_implicit_fields = self.construct_implicit_fields();
 
             // testme: transform
 
@@ -267,15 +267,15 @@ pub mod context_selector {
                         #error_constructor_name {
                             #empty_source_field
                             #message_field_name: message,
-                            #construct_backtrace_field
+                            #construct_implicit_fields
                         }
                     }
 
                     fn with_source(error: Self::Source, message: String) -> Self {
                         #error_constructor_name {
                             #transfer_source_field
                             #message_field_name: message,
-                            #construct_backtrace_field
+                            #construct_implicit_fields
                         }
                     }
                 }
@@ -285,7 +285,7 @@ pub mod context_selector {
         fn generate_from_source(self, source_field: &crate::SourceField) -> TokenStream {
             let parameterized_error_name = self.parameterized_error_name;
             let error_constructor_name = self.error_constructor_name;
-            let construct_backtrace_field = self.construct_backtrace_field();
+            let construct_implicit_fields = self.construct_implicit_fields();
             let original_generics_without_defaults = self.original_generics_without_defaults;
             let user_field_generics = self.user_field_generics();
             let where_clauses = self.where_clauses;
@@ -300,7 +300,7 @@ pub mod context_selector {
                     fn from(error: #source_field_type) -> Self {
                         #error_constructor_name {
                             #transfer_source_field
-                            #construct_backtrace_field
+                            #construct_implicit_fields
                         }
                     }
                 }
@@ -633,7 +633,7 @@ pub mod error_compat {
                         name: field_name, ..
                     } = backtrace_field;
                     quote! {
-                        #pattern_ident { ref #field_name, .. } => { #crate_root::GenerateBacktrace::as_backtrace(#field_name) }
+                        #pattern_ident { ref #field_name, .. } => { #crate_root::AsBacktrace::as_backtrace(#field_name) }
                     }
                 }
                 _ => {

src/backtrace_inert.rs

@@ -7,11 +7,13 @@ use core::fmt;
 #[derive(Debug)]
 pub struct Backtrace(());
 
-impl crate::GenerateBacktrace for Backtrace {
+impl crate::GenerateImplicitData for Backtrace {
     fn generate() -> Self {
         Backtrace(())
     }
+}
 
+impl crate::AsBacktrace for Backtrace {
     fn as_backtrace(&self) -> Option<&Backtrace> {
         Some(self)
     }

src/backtrace_shim.rs

@@ -8,13 +8,15 @@ use std::{fmt, path};
 #[derive(Debug)]
 pub struct Backtrace(backtrace::Backtrace);
 
-impl crate::GenerateBacktrace for Backtrace {
+impl crate::GenerateImplicitData for Backtrace {
     // Inlining in an attempt to remove this function from the backtrace
     #[inline(always)]
     fn generate() -> Self {
         Backtrace(backtrace::Backtrace::new())
     }
+}
 
+impl crate::AsBacktrace for Backtrace {
     fn as_backtrace(&self) -> Option<&Backtrace> {
         Some(self)
     }

src/guide/examples/backtrace.rs

@@ -2,7 +2,7 @@
 //!
 //! Start by looking at the error type [`Error`].
 
-use crate::{Snafu, Backtrace, ErrorCompat, GenerateBacktrace};
+use crate::{Snafu, Backtrace, ErrorCompat, GenerateImplicitData};
 
 /// Backtraces aren't yet supported by the stable Rust compiler. SNAFU
 /// provides a stable-compatible way of getting backtraces as well as
@@ -70,10 +70,10 @@ pub enum Error {
 
     /// When an error is expected to be created frequently but the
     /// backtrace is rarely needed, you can wrap it in an
-    /// `Option`. See
-    /// [GenerateBacktrace](GenerateBacktrace#impl-GenerateBacktrace-for-Option<Backtrace>)
-    /// for instructions on how to access the backtrace in this
-    /// case.
+    /// `Option`. See [the instructions][] on how to access the
+    /// backtrace in this case.
+    ///
+    /// [the instructions]: GenerateImplicitData#impl-GenerateImplicitData-for-Option<Backtrace>
     UsedInTightLoop {
         backtrace: Option<Backtrace>,
     },

src/lib.rs

@@ -1020,11 +1020,15 @@ pub trait FromString {
     fn with_source(source: Self::Source, message: String) -> Self;
 }
 
-/// Construct a backtrace, allowing it to be optional.
-pub trait GenerateBacktrace {
-    /// Generate a new backtrace instance
+/// Construct data to be included as part of an error. The data must
+/// require no arguments to be created.
+pub trait GenerateImplicitData {
+    /// Build the data.
     fn generate() -> Self;
+}
 
+/// View a backtrace-like value as an optional backtrace.
+pub trait AsBacktrace {
     /// Retrieve the optional backtrace
     fn as_backtrace(&self) -> Option<&Backtrace>;
 }
@@ -1039,7 +1043,7 @@ pub trait GenerateBacktrace {
 /// changing the environment variable after it has been checked will
 /// have no effect.
 #[cfg(any(feature = "std", test))]
-impl GenerateBacktrace for Option<Backtrace> {
+impl GenerateImplicitData for Option<Backtrace> {
     fn generate() -> Self {
         use std::env;
         use std::sync::{
@@ -1064,29 +1068,38 @@ impl GenerateBacktrace for Option<Backtrace> {
             None
         }
     }
+}
 
+#[cfg(any(feature = "std", test))]
+impl AsBacktrace for Option<Backtrace> {
     fn as_backtrace(&self) -> Option<&Backtrace> {
         self.as_ref()
     }
 }
 
 #[cfg(feature = "backtraces-impl-backtrace-crate")]
-impl GenerateBacktrace for Backtrace {
+impl GenerateImplicitData for Backtrace {
     fn generate() -> Self {
         Backtrace::new()
     }
+}
 
+#[cfg(feature = "backtraces-impl-backtrace-crate")]
+impl AsBacktrace for Backtrace {
     fn as_backtrace(&self) -> Option<&Backtrace> {
         Some(self)
     }
 }
 
 #[cfg(feature = "unstable-backtraces-impl-std")]
-impl GenerateBacktrace for Backtrace {
+impl GenerateImplicitData for Backtrace {
     fn generate() -> Self {
         Backtrace::force_capture()
     }
+}
 
+#[cfg(feature = "unstable-backtraces-impl-std")]
+impl AsBacktrace for Backtrace {
     fn as_backtrace(&self) -> Option<&Backtrace> {
         Some(self)
     }