Implement support for no_std

This brings no_std support to SNAFU. It now has a `std` feature which
is activated by default. To make no_std support as frictionless as
possible, SNAFU now reexports the `std::error::Error` trait as
`snafu::Error` when the feature is activated and defines its own API
compatible trait instead when it's disabled.

In order to not commit to having a publicly visible copy of the
`Error` trait in SNAFU, hiding it from the documentation allows for
SNAFU to still support all of its features, but the user never gets to
use the trait. This way SNAFU can switch out the trait at any point
with `core::error::Error` if that becomes a thing. Alternatively the
trait here can also be made visible at some point. Both of these
possibilities are not breaking, so the conservative approach with
`doc(hidden)` allows for the smoothest experience going forward.

Resolves #85

.cirrus.yml

@@ -27,6 +27,22 @@ stable_test_task:
     - cargo fmt --all -- --check
   before_cache_script: rm -rf $CARGO_HOME/registry/index
 
+no_std_test_task:
+  name: "Rust Stable (no_std)"
+  container:
+    image: rust:latest
+    cpu: 1
+    memory: 2Gi
+  cargo_cache:
+    folder: $CARGO_HOME/registry
+    fingerprint_script: cat Cargo.toml
+  setup_script:
+    - rustup target add thumbv6m-none-eabi
+  primary_test_script:
+    - rustc --version
+    - cargo build --no-default-features --target thumbv6m-none-eabi
+  before_cache_script: rm -rf $CARGO_HOME/registry/index
+
 nightly_test_task:
   name: "Rust Nightly"
   container:

Cargo.toml

@@ -11,8 +11,8 @@ repository = "https://github.com/shepmaster/snafu"
 
 license = "MIT OR Apache-2.0"
 
-keywords = ["error", "ergonomic", "library"]
-categories = ["rust-patterns"]
+keywords = ["error", "ergonomic", "library", "no_std"]
+categories = ["rust-patterns", "no-std"]
 
 exclude = [
   "/.cirrus.yml",
@@ -24,10 +24,13 @@ exclude = [
 all-features = true
 
 [features]
-default = ["backtraces"]
+default = ["backtraces", "std"]
+
+# Implement the `std::error::Error` trait.
+std = []
 
 # Adds the backtrace type
-backtraces = ["snafu-derive/backtraces", "backtrace"]
+backtraces = ["std", "snafu-derive/backtraces", "backtrace"]
 
 # Add conversion to `backtrace::Backtrace`
 backtrace-crate = ["backtraces"]

compatibility-tests/without-backtrace/Cargo.toml

@@ -5,4 +5,4 @@ authors = ["Jake Goulding <[email protected]>"]
 edition = "2018"
 
 [dependencies]
-snafu = { path = "../..", default-features = false, features = [] }
+snafu = { path = "../..", default-features = false, features = ["std"] }

snafu-derive/src/lib.rs

@@ -1298,7 +1298,7 @@ impl<'a> quote::ToTokens for ContextSelector<'a> {
         let backtrace_field = match *backtrace_field {
             Some(ref field) => {
                 let name = &field.name;
-                quote! { #name: std::default::Default::default(), }
+                quote! { #name: core::default::Default::default(), }
             }
             None => quote! {},
         };
@@ -1308,7 +1308,7 @@ impl<'a> quote::ToTokens for ContextSelector<'a> {
             .zip(user_fields)
             .map(|(gen_ty, f)| {
                 let Field { ref ty, .. } = *f;
-                quote! { #gen_ty: std::convert::Into<#ty> }
+                quote! { #gen_ty: core::convert::Into<#ty> }
             })
             .chain(self.0.provided_where_clauses())
             .collect();
@@ -1318,16 +1318,16 @@ impl<'a> quote::ToTokens for ContextSelector<'a> {
                 impl<#(#generic_names,)*> #selector_name
                 {
                     #[doc = "Consume the selector and return a `Result` with the associated error"]
-                    #visibility fn fail<#(#original_generics_without_defaults,)* __T>(self) -> std::result::Result<__T, #parameterized_enum_name>
+                    #visibility fn fail<#(#original_generics_without_defaults,)* __T>(self) -> core::result::Result<__T, #parameterized_enum_name>
                     where
                         #(#where_clauses),*
                     {
                         let Self { #(#names),* } = self;
                         let error = #enum_name::#variant_name {
                             #backtrace_field
-                            #( #names: std::convert::Into::into(#names) ),*
+                            #( #names: core::convert::Into::into(#names) ),*
                         };
-                        std::result::Result::Err(error)
+                        core::result::Result::Err(error)
                     }
                 }
             }
@@ -1367,7 +1367,7 @@ impl<'a> quote::ToTokens for ContextSelector<'a> {
             quote! {
                 impl#generics_list snafu::IntoError<#parameterized_enum_name> for #selector_name
                 where
-                    #parameterized_enum_name: std::error::Error + snafu::ErrorCompat,
+                    #parameterized_enum_name: snafu::Error + snafu::ErrorCompat,
                     #(#where_clauses),*
                 {
                     type Source = #source_ty;
@@ -1453,11 +1453,11 @@ impl<'a> quote::ToTokens for DisplayImpl<'a> {
 
         stream.extend({
             quote! {
-                impl<#(#original_generics),*> std::fmt::Display for #parameterized_enum_name
+                impl<#(#original_generics),*> core::fmt::Display for #parameterized_enum_name
                 where
                     #(#where_clauses),*
                 {
-                    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+                    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
                         #[allow(unused_variables)]
                         match *self {
                             #(#variants_to_display)*
@@ -1509,13 +1509,13 @@ impl<'a> ErrorImpl<'a> {
                         } = *source_field;
                         quote! {
                             #enum_name::#variant_name { ref #field_name, .. } => {
-                                std::option::Option::Some(#field_name.as_error_source())
+                                core::option::Option::Some(#field_name.as_error_source())
                             }
                         }
                     }
                     None => {
                         quote! {
-                            #enum_name::#variant_name { .. } => { std::option::Option::None }
+                            #enum_name::#variant_name { .. } => { core::option::Option::None }
                         }
                     }
                 }
@@ -1543,7 +1543,7 @@ impl<'a> quote::ToTokens for ErrorImpl<'a> {
         let variants_to_source = &self.variants_to_source();
 
         let cause_fn = quote! {
-            fn cause(&self) -> Option<&dyn std::error::Error> {
+            fn cause(&self) -> Option<&dyn snafu::Error> {
                 use snafu::AsErrorSource;
                 match *self {
                     #(#variants_to_source)*
@@ -1552,7 +1552,7 @@ impl<'a> quote::ToTokens for ErrorImpl<'a> {
         };
 
         let source_fn = quote! {
-            fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+            fn source(&self) -> Option<&(dyn snafu::Error + 'static)> {
                 use snafu::AsErrorSource;
                 match *self {
                     #(#variants_to_source)*
@@ -1562,9 +1562,9 @@ impl<'a> quote::ToTokens for ErrorImpl<'a> {
 
         stream.extend({
             quote! {
-                impl<#(#original_generics),*> std::error::Error for #parameterized_enum_name
+                impl<#(#original_generics),*> snafu::Error for #parameterized_enum_name
                 where
-                    Self: std::fmt::Debug + std::fmt::Display,
+                    Self: core::fmt::Debug + core::fmt::Display,
                     #(#where_clauses),*
                 {
                     #description_fn
@@ -1606,12 +1606,12 @@ impl<'a> ErrorCompatImpl<'a> {
                         ..
                     } = *backtrace_field;
                     quote! {
-                        #enum_name::#variant_name { ref #field_name, .. } => { std::option::Option::Some(#field_name) }
+                        #enum_name::#variant_name { ref #field_name, .. } => { core::option::Option::Some(#field_name) }
                     }
                 }
                 _ => {
                     quote! {
-                        #enum_name::#variant_name { .. } => { std::option::Option::None }
+                        #enum_name::#variant_name { .. } => { core::option::Option::None }
                     }
                 }
             }
@@ -1673,19 +1673,19 @@ impl StructInfo {
 
         let description_fn = quote! {
             fn description(&self) -> &str {
-                std::error::Error::description(&self.0)
+                snafu::Error::description(&self.0)
             }
         };
 
         let cause_fn = quote! {
-            fn cause(&self) -> Option<&dyn std::error::Error> {
-                std::error::Error::cause(&self.0)
+            fn cause(&self) -> Option<&dyn snafu::Error> {
+                snafu::Error::cause(&self.0)
             }
         };
 
         let source_fn = quote! {
-            fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
-                std::error::Error::source(&self.0)
+            fn source(&self) -> Option<&(dyn snafu::Error + 'static)> {
+                snafu::Error::source(&self.0)
             }
         };
 
@@ -1700,7 +1700,7 @@ impl StructInfo {
         };
 
         let error_impl = quote! {
-            impl#generics std::error::Error for #parameterized_struct_name
+            impl#generics snafu::Error for #parameterized_struct_name
             where
                 #(#where_clauses),*
             {
@@ -1720,18 +1720,18 @@ impl StructInfo {
         };
 
         let display_impl = quote! {
-            impl#generics std::fmt::Display for #parameterized_struct_name
+            impl#generics core::fmt::Display for #parameterized_struct_name
             where
                 #(#where_clauses),*
             {
-                fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-                    std::fmt::Display::fmt(&self.0, f)
+                fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+                    core::fmt::Display::fmt(&self.0, f)
                 }
             }
         };
 
         let from_impl = quote! {
-            impl#generics std::convert::From<#inner_type> for #parameterized_struct_name
+            impl#generics core::convert::From<#inner_type> for #parameterized_struct_name
             where
                 #(#where_clauses),*
             {

src/futures/try_future.rs

@@ -2,15 +2,15 @@
 //!
 //! [`TryFuture`]: futures_core::future::TryFuture
 
-use crate::{ErrorCompat, IntoError};
-use futures_core::future::TryFuture;
-use pin_project::pin_project;
-use std::{
+use crate::{Error, ErrorCompat, IntoError};
+use core::{
     future::Future,
     marker::PhantomData,
     pin::Pin,
     task::{Context as TaskContext, Poll},
 };
+use futures_core::future::TryFuture;
+use pin_project::pin_project;
 
 /// Additions to [`TryFuture`].
 pub trait TryFutureExt: TryFuture + Sized {
@@ -49,7 +49,7 @@ pub trait TryFutureExt: TryFuture + Sized {
     fn context<C, E>(self, context: C) -> Context<Self, C, E>
     where
         C: IntoError<E, Source = Self::Error>,
-        E: std::error::Error + ErrorCompat;
+        E: Error + ErrorCompat;
 
     /// Extend a [`TryFuture`]'s error with lazily-generated context-sensitive
     /// information.
@@ -87,7 +87,7 @@ pub trait TryFutureExt: TryFuture + Sized {
     where
         F: FnOnce() -> C,
         C: IntoError<E, Source = Self::Error>,
-        E: std::error::Error + ErrorCompat;
+        E: Error + ErrorCompat;
 }
 
 impl<Fut> TryFutureExt for Fut
@@ -97,7 +97,7 @@ where
     fn context<C, E>(self, context: C) -> Context<Self, C, E>
     where
         C: IntoError<E, Source = Self::Error>,
-        E: std::error::Error + ErrorCompat,
+        E: Error + ErrorCompat,
     {
         Context {
             inner: self,
@@ -110,7 +110,7 @@ where
     where
         F: FnOnce() -> C,
         C: IntoError<E, Source = Self::Error>,
-        E: std::error::Error + ErrorCompat,
+        E: Error + ErrorCompat,
     {
         WithContext {
             inner: self,
@@ -137,7 +137,7 @@ impl<Fut, C, E> Future for Context<Fut, C, E>
 where
     Fut: TryFuture,
     C: IntoError<E, Source = Fut::Error>,
-    E: std::error::Error + ErrorCompat,
+    E: Error + ErrorCompat,
 {
     type Output = Result<Fut::Ok, E>;
 
@@ -173,7 +173,7 @@ where
     Fut: TryFuture,
     F: FnOnce() -> C,
     C: IntoError<E, Source = Fut::Error>,
-    E: std::error::Error + ErrorCompat,
+    E: Error + ErrorCompat,
 {
     type Output = Result<Fut::Ok, E>;
 

src/futures/try_stream.rs

@@ -2,14 +2,14 @@
 //!
 //! [`TryStream`]: futures_core::TryStream
 
-use crate::{ErrorCompat, IntoError};
-use futures_core::stream::{Stream, TryStream};
-use pin_project::pin_project;
-use std::{
+use crate::{Error, ErrorCompat, IntoError};
+use core::{
     marker::PhantomData,
     pin::Pin,
     task::{Context as TaskContext, Poll},
 };
+use futures_core::stream::{Stream, TryStream};
+use pin_project::pin_project;
 
 /// Additions to [`TryStream`].
 pub trait TryStreamExt: TryStream + Sized {
@@ -49,7 +49,7 @@ pub trait TryStreamExt: TryStream + Sized {
     fn context<C, E>(self, context: C) -> Context<Self, C, E>
     where
         C: IntoError<E, Source = Self::Error> + Clone,
-        E: std::error::Error + ErrorCompat;
+        E: Error + ErrorCompat;
 
     /// Extend a [`TryStream`]'s error with lazily-generated
     /// context-sensitive information.
@@ -88,7 +88,7 @@ pub trait TryStreamExt: TryStream + Sized {
     where
         F: FnMut() -> C,
         C: IntoError<E, Source = Self::Error>,
-        E: std::error::Error + ErrorCompat;
+        E: Error + ErrorCompat;
 }
 
 impl<St> TryStreamExt for St
@@ -98,7 +98,7 @@ where
     fn context<C, E>(self, context: C) -> Context<Self, C, E>
     where
         C: IntoError<E, Source = Self::Error> + Clone,
-        E: std::error::Error + ErrorCompat,
+        E: Error + ErrorCompat,
     {
         Context {
             inner: self,
@@ -111,7 +111,7 @@ where
     where
         F: FnMut() -> C,
         C: IntoError<E, Source = Self::Error>,
-        E: std::error::Error + ErrorCompat,
+        E: Error + ErrorCompat,
     {
         WithContext {
             inner: self,
@@ -138,7 +138,7 @@ impl<St, C, E> Stream for Context<St, C, E>
 where
     St: TryStream,
     C: IntoError<E, Source = St::Error> + Clone,
-    E: std::error::Error + ErrorCompat,
+    E: Error + ErrorCompat,
 {
     type Item = Result<St::Ok, E>;
 
@@ -177,7 +177,7 @@ where
     St: TryStream,
     F: FnMut() -> C,
     C: IntoError<E, Source = St::Error>,
-    E: std::error::Error + ErrorCompat,
+    E: Error + ErrorCompat,
 {
     type Item = Result<St::Ok, E>;