From 0911289db829803f19002735dd75c3f20cc28f88 Mon Sep 17 00:00:00 2001
From: Chris Beck <beck.ct@gmail.com>
Date: Thu, 12 Sep 2019 14:47:19 -0700
Subject: [PATCH] Fixup prost-derive dependency on std-only features of failure
 crate

---
 prost-derive/Cargo.toml |  1 -
 prost-derive/src/lib.rs | 30 ++++++++++++++++++++++--------
 2 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/prost-derive/Cargo.toml b/prost-derive/Cargo.toml
index c89da0b4e..905962bbd 100644
--- a/prost-derive/Cargo.toml
+++ b/prost-derive/Cargo.toml
@@ -29,7 +29,6 @@ use_std = [ "failure/std" ]
 default = []
 
 [dependencies]
-failure = { version = "0.1", default-features = false }
 itertools = "0.8"
 proc-macro2 = "0.4.4"
 quote = "0.6.3"
diff --git a/prost-derive/src/lib.rs b/prost-derive/src/lib.rs
index 646534a46..7460c6752 100644
--- a/prost-derive/src/lib.rs
+++ b/prost-derive/src/lib.rs
@@ -5,10 +5,8 @@
 extern crate proc_macro;
 extern crate alloc;
 
-use failure::bail;
 use quote::quote;
 
-use failure::Error;
 use itertools::Itertools;
 use proc_macro::TokenStream;
 use proc_macro2::Span;
@@ -20,7 +18,23 @@ use syn::{
 mod field;
 use crate::field::Field;
 
-fn try_message(input: TokenStream) -> Result<TokenStream, Error> {
+// Note: Historically we used failure::bail!, but this requires std feature in failure
+// which makes it incompatible with any no_std targets that use failure crate, since
+// cargo will perform feature unification
+//
+// This drops std::error::Error and replaces it with String, and makes bail! produce a string.
+// It also drops our dependency on failure crate entirely.
+use alloc::string::String;
+macro_rules! bail {
+    ($e:expr) => {
+        return Err(($e).into());
+    };
+    ($fmt:expr, $($arg:tt)*) => {
+        return Err(format!($fmt, $($arg)*));
+    };
+}
+
+fn try_message(input: TokenStream) -> Result<TokenStream, String> {
     let input: DeriveInput = syn::parse(input)?;
 
     let ident = input.ident;
@@ -68,11 +82,11 @@ fn try_message(input: TokenStream) -> Result<TokenStream, Error> {
                 }
                 Ok(None) => None,
                 Err(err) => Some(Err(
-                    err.context(format!("invalid message field {}.{}", ident, field_ident))
+                    format!("invalid message field {}.{}\n{}", ident, field_ident, err))
                 )),
             }
         })
-        .collect::<Result<Vec<(Ident, Field)>, failure::Context<String>>>()?;
+        .collect::<Result<Vec<(Ident, Field)>, String>>()?;
 
     // We want Debug to be in declaration order
     let unsorted_fields = fields.clone();
@@ -239,7 +253,7 @@ pub fn message(input: TokenStream) -> TokenStream {
     try_message(input).unwrap()
 }
 
-fn try_enumeration(input: TokenStream) -> Result<TokenStream, Error> {
+fn try_enumeration(input: TokenStream) -> Result<TokenStream, String> {
     let input: DeriveInput = syn::parse(input)?;
     let ident = input.ident;
 
@@ -340,7 +354,7 @@ pub fn enumeration(input: TokenStream) -> TokenStream {
     try_enumeration(input).unwrap()
 }
 
-fn try_oneof(input: TokenStream) -> Result<TokenStream, Error> {
+fn try_oneof(input: TokenStream) -> Result<TokenStream, String> {
     let input: DeriveInput = syn::parse(input)?;
 
     let ident = input.ident;
@@ -382,7 +396,7 @@ fn try_oneof(input: TokenStream) -> Result<TokenStream, Error> {
 
     let mut tags = fields
         .iter()
-        .flat_map(|&(ref variant_ident, ref field)| -> Result<u32, Error> {
+        .flat_map(|&(ref variant_ident, ref field)| -> Result<u32, String> {
             if field.tags().len() > 1 {
                 bail!(
                     "invalid oneof variant {}::{}: oneof variants may only have a single tag",