Support no_std

Cargo.toml

@@ -14,13 +14,17 @@ readme = "README.md"
 travis-ci = { repository = "dtolnay/thiserror" }
 
 [dependencies]
-thiserror-impl = { version = "=1.0.11", path = "impl" }
+thiserror-impl = { version = "=1.0.11", path = "impl", default-features = false }
 
 [dev-dependencies]
 anyhow = "1.0"
 ref-cast = "1.0"
 rustversion = "1.0"
 trybuild = { version = "1.0.19", features = ["diff"] }
 
+[features]
+default = ["std"]
+std = ["thiserror-impl/std"]
+
 [workspace]
 members = ["impl"]

impl/Cargo.toml

@@ -17,3 +17,7 @@ travis-ci = { repository = "dtolnay/thiserror" }
 proc-macro2 = "1.0"
 quote = "1.0"
 syn = "1.0.11"
+
+[features]
+default = ["std"]
+std = []

impl/src/expand.rs

@@ -1,6 +1,9 @@
 use crate::ast::{Enum, Field, Input, Struct};
 use proc_macro2::TokenStream;
-use quote::{format_ident, quote, quote_spanned, ToTokens};
+#[cfg(feature = "std")]
+use quote::quote_spanned;
+use quote::{format_ident, quote, ToTokens};
+#[cfg(feature = "std")]
 use syn::spanned::Spanned;
 use syn::{DeriveInput, Member, PathArguments, Result, Type};
 
@@ -17,6 +20,7 @@ fn impl_struct(input: Struct) -> TokenStream {
     let ty = &input.ident;
     let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
 
+    #[cfg(feature = "std")]
     let source_body = if input.attrs.transparent.is_some() {
         let only_field = &input.fields[0].member;
         Some(quote! {
@@ -36,6 +40,7 @@ fn impl_struct(input: Struct) -> TokenStream {
     } else {
         None
     };
+    #[cfg(feature = "std")]
     let source_method = source_body.map(|body| {
         quote! {
             fn source(&self) -> std::option::Option<&(dyn std::error::Error + 'static)> {
@@ -45,6 +50,7 @@ fn impl_struct(input: Struct) -> TokenStream {
         }
     });
 
+    #[cfg(feature = "std")]
     let backtrace_method = input.backtrace_field().map(|backtrace_field| {
         let backtrace = &backtrace_field.member;
         let body = if let Some(source_field) = input.source_field() {
@@ -96,7 +102,10 @@ fn impl_struct(input: Struct) -> TokenStream {
         let use_as_display = if display.has_bonus_display {
             Some(quote! {
                 #[allow(unused_imports)]
-                use thiserror::private::{DisplayAsDisplay, PathAsDisplay};
+                use thiserror::private::DisplayAsDisplay;
+                #[cfg(feature = "std")]
+                #[allow(unused_imports)]
+                use thiserror::private::PathAsDisplay;
             })
         } else {
             None
@@ -126,19 +135,26 @@ fn impl_struct(input: Struct) -> TokenStream {
         let from = from_field.ty;
         let body = from_initializer(from_field, backtrace_field);
         quote! {
-            impl #impl_generics std::convert::From<#from> for #ty #ty_generics #where_clause {
+            impl #impl_generics core::convert::From<#from> for #ty #ty_generics #where_clause {
                 fn from(source: #from) -> Self {
                     #ty #body
                 }
             }
         }
     });
 
-    quote! {
+    #[cfg(feature = "std")]
+    let error_impl = quote! {
         impl #impl_generics std::error::Error for #ty #ty_generics #where_clause {
             #source_method
             #backtrace_method
         }
+    };
+    #[cfg(not(feature = "std"))]
+    let error_impl = quote! {};
+
+    quote! {
+        #error_impl
         #display_impl
         #from_impl
     }
@@ -148,6 +164,7 @@ fn impl_enum(input: Enum) -> TokenStream {
     let ty = &input.ident;
     let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
 
+    #[cfg(feature = "std")]
     let source_method = if input.has_source() {
         let arms = input.variants.iter().map(|variant| {
             let ident = &variant.ident;
@@ -186,6 +203,7 @@ fn impl_enum(input: Enum) -> TokenStream {
         None
     };
 
+    #[cfg(feature = "std")]
     let backtrace_method = if input.has_backtrace() {
         let arms = input.variants.iter().map(|variant| {
             let ident = &variant.ident;
@@ -260,7 +278,10 @@ fn impl_enum(input: Enum) -> TokenStream {
         }) {
             Some(quote! {
                 #[allow(unused_imports)]
-                use thiserror::private::{DisplayAsDisplay, PathAsDisplay};
+                use thiserror::private::DisplayAsDisplay;
+                #[allow(unused_imports)]
+                #[cfg(feature = "std")]
+                use thiserror::private::PathAsDisplay;
             })
         } else {
             None
@@ -309,19 +330,26 @@ fn impl_enum(input: Enum) -> TokenStream {
         let from = from_field.ty;
         let body = from_initializer(from_field, backtrace_field);
         Some(quote! {
-            impl #impl_generics std::convert::From<#from> for #ty #ty_generics #where_clause {
+            impl #impl_generics core::convert::From<#from> for #ty #ty_generics #where_clause {
                 fn from(source: #from) -> Self {
                     #ty::#variant #body
                 }
             }
         })
     });
 
-    quote! {
+    #[cfg(feature = "std")]
+    let error_impl = quote! {
         impl #impl_generics std::error::Error for #ty #ty_generics #where_clause {
             #source_method
             #backtrace_method
         }
+    };
+    #[cfg(not(feature = "std"))]
+    let error_impl = quote! {};
+
+    quote! {
+        #error_impl
         #display_impl
         #(#from_impls)*
     }

impl/src/prop.rs

@@ -1,11 +1,14 @@
 use crate::ast::{Enum, Field, Struct, Variant};
-use syn::{Member, Type};
+#[cfg(feature = "std")]
+use syn::Member;
+use syn::Type;
 
 impl Struct<'_> {
     pub(crate) fn from_field(&self) -> Option<&Field> {
         from_field(&self.fields)
     }
 
+    #[cfg(feature = "std")]
     pub(crate) fn source_field(&self) -> Option<&Field> {
         source_field(&self.fields)
     }
@@ -16,12 +19,14 @@ impl Struct<'_> {
 }
 
 impl Enum<'_> {
+    #[cfg(feature = "std")]
     pub(crate) fn has_source(&self) -> bool {
         self.variants
             .iter()
             .any(|variant| variant.source_field().is_some() || variant.attrs.transparent.is_some())
     }
 
+    #[cfg(feature = "std")]
     pub(crate) fn has_backtrace(&self) -> bool {
         self.variants
             .iter()
@@ -47,6 +52,7 @@ impl Variant<'_> {
         from_field(&self.fields)
     }
 
+    #[cfg(feature = "std")]
     pub(crate) fn source_field(&self) -> Option<&Field> {
         source_field(&self.fields)
     }
@@ -71,6 +77,7 @@ fn from_field<'a, 'b>(fields: &'a [Field<'b>]) -> Option<&'a Field<'b>> {
     None
 }
 
+#[cfg(feature = "std")]
 fn source_field<'a, 'b>(fields: &'a [Field<'b>]) -> Option<&'a Field<'b>> {
     for field in fields {
         if field.attrs.from.is_some() || field.attrs.source.is_some() {

src/display.rs

@@ -1,4 +1,5 @@
 use std::fmt::Display;
+#[cfg(feature = "std")]
 use std::path::{self, Path, PathBuf};
 
 pub trait DisplayAsDisplay {
@@ -11,16 +12,19 @@ impl<T: Display> DisplayAsDisplay for &T {
     }
 }
 
+#[cfg(feature = "std")]
 pub trait PathAsDisplay {
     fn as_display(&self) -> path::Display<'_>;
 }
 
+#[cfg(feature = "std")]
 impl PathAsDisplay for Path {
     fn as_display(&self) -> path::Display<'_> {
         self.display()
     }
 }
 
+#[cfg(feature = "std")]
 impl PathAsDisplay for PathBuf {
     fn as_display(&self) -> path::Display<'_> {
         self.display()

src/lib.rs

@@ -176,6 +176,20 @@
 //!
 //!   [`anyhow`]: https://github.com/dtolnay/anyhow
 
+// Always enabled to force devs to add use statements for things like Vec and String, even when
+// working with std.
+#![no_std]
+
+#[cfg(not(feature = "std"))]
+#[allow(unused_imports)]
+#[macro_use]
+extern crate alloc as std;
+#[cfg(feature = "std")]
+#[allow(unused_imports)]
+#[macro_use]
+extern crate std;
+
+#[cfg(feature = "std")]
 mod aserror;
 mod display;
 
@@ -184,6 +198,9 @@ pub use thiserror_impl::*;
 // Not public API.
 #[doc(hidden)]
 pub mod private {
+    #[cfg(feature = "std")]
     pub use crate::aserror::AsDynError;
-    pub use crate::display::{DisplayAsDisplay, PathAsDisplay};
+    pub use crate::display::DisplayAsDisplay;
+    #[cfg(feature = "std")]
+    pub use crate::display::PathAsDisplay;
 }