From f041a64fca8ff76123adf5c49d34f7e32f9bcd26 Mon Sep 17 00:00:00 2001
From: Jeffrey Czyz <jkczyz@gmail.com>
Date: Thu, 3 Mar 2022 23:59:44 -0800
Subject: [PATCH] Check for no-std compatibility across dependencies

To ensure no-std is honored across dependencies, add a crate depending
on lightning crates supporting no-std. This should ensure any
regressions are caught. Otherwise, cargo doesn't seem to catch some
incompatibilities (e.g., f64::log10 unavailable in core) and seemingly
across other dependencies as describe here:

https://blog.dbrgn.ch/2019/12/24/testing-for-no-std-compatibility/
---
 .github/workflows/build.yml |  4 ++++
 .gitignore                  |  1 +
 Cargo.toml                  |  4 ++++
 no-std-check/Cargo.toml     | 11 +++++++++++
 no-std-check/src/lib.rs     |  0
 5 files changed, 20 insertions(+)
 create mode 100644 no-std-check/Cargo.toml
 create mode 100644 no-std-check/src/lib.rs

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index a4eec2bbc..e894b4947 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -122,6 +122,10 @@ jobs:
           cargo test --verbose --color always --no-default-features --features no-std
           # check if there is a conflict between no-std and the default std feature
           cargo test --verbose --color always --features no-std
+          # check no-std compatibility across dependencies
+          cd ..
+          cd no-std-check
+          cargo check --verbose --color always
           cd ..
       - name: Test on no-std builds Rust ${{ matrix.toolchain }} and full code-linking for coverage generation
         if: "matrix.build-no-std && matrix.coverage"
diff --git a/.gitignore b/.gitignore
index a108267c2..10e905af5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,3 +8,4 @@ lightning-c-bindings/a.out
 Cargo.lock
 .idea
 lightning/target
+no-std-check/target
diff --git a/Cargo.toml b/Cargo.toml
index df32ac5d9..6e03fc1ac 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,6 +9,10 @@ members = [
     "lightning-background-processor",
 ]
 
+exclude = [
+    "no-std-check",
+]
+
 # Our tests do actual crypo and lots of work, the tradeoff for -O1 is well worth it.
 # Ideally we would only do this in profile.test, but profile.test only applies to
 # the test binary, not dependencies, which means most of the critical code still
diff --git a/no-std-check/Cargo.toml b/no-std-check/Cargo.toml
new file mode 100644
index 000000000..15d2c196c
--- /dev/null
+++ b/no-std-check/Cargo.toml
@@ -0,0 +1,11 @@
+[package]
+name = "no-std-check"
+version = "0.1.0"
+edition = "2018"
+
+[features]
+default = ["lightning/no-std", "lightning-invoice/no-std"]
+
+[dependencies]
+lightning = { path = "../lightning", default-features = false }
+lightning-invoice = { path = "../lightning-invoice", default-features = false }
diff --git a/no-std-check/src/lib.rs b/no-std-check/src/lib.rs
new file mode 100644
index 000000000..e69de29bb
-- 
2.39.5