From b40ec7135e843bef06c8fa3b93217f47cf34e7f9 Mon Sep 17 00:00:00 2001
From: David Kotval <kotval@protonmail.com>
Date: Fri, 1 Mar 2024 13:54:05 -0600
Subject: [PATCH] wip: returning to cfg based dependency specification

---
 curve25519-dalek/Cargo.toml   | 12 ++++++------
 curve25519-dalek/build.rs     |  4 +++-
 curve25519-dalek/src/field.rs |  1 +
 curve25519-dalek/src/lib.rs   | 15 +++------------
 4 files changed, 13 insertions(+), 19 deletions(-)

diff --git a/curve25519-dalek/Cargo.toml b/curve25519-dalek/Cargo.toml
index fd89fbf..e8cdce9 100644
--- a/curve25519-dalek/Cargo.toml
+++ b/curve25519-dalek/Cargo.toml
@@ -57,10 +57,12 @@ serde = { version = "1.0", default-features = false, optional = true, features =
 zeroize = { version = "1", default-features = false, optional = true }
 
 # Betrusted/Precursor dependency set, enabled by backend_u32e feature
-log = { version = "0.4", optional = true}
-engine25519-as = {git = "https://github.com/betrusted-io/engine25519-as.git", rev = "d249c967556b02ab5439eacb5078fa00c60b93d6", default-features = false, features = [], optional = true}
-engine-25519 = { git = "https://github.com/betrusted-io/xous-engine-25519.git", rev = "63d3d1f30736022e791deaacf4dd62c00b42fe2e", optional = true}
-utralib = {version = "0.1.24", default-features = false, optional = true}
+[target.'cfg(curve25519_dalek_backend = "u32e_backend")'.dependencies]
+log = { version = "0.4"}
+engine25519-as = {git = "https://github.com/betrusted-io/engine25519-as.git", rev = "d249c967556b02ab5439eacb5078fa00c60b93d6", default-features = false, features = []}
+engine-25519 = { git = "https://github.com/betrusted-io/xous-engine-25519.git", rev = "63d3d1f30736022e791deaacf4dd62c00b42fe2e"}
+utralib = {version = "0.1.24", default-features = false}
+
 
 [target.'cfg(target_arch = "x86_64")'.dependencies]
 cpufeatures = "0.2.6"
@@ -72,8 +74,6 @@ default = ["alloc", "precomputed-tables", "zeroize"]
 alloc = ["zeroize?/alloc"]
 precomputed-tables = []
 legacy_compatibility = []
-fiat_backend = ["dep:fiat-crypto"]
-u32e_backend = ["dep:engine25519-as","dep:engine-25519","dep:utralib","log","zeroize"]
 group = ["dep:group", "rand_core"]
 group-bits = ["group", "ff/bits"]
 
diff --git a/curve25519-dalek/build.rs b/curve25519-dalek/build.rs
index aeed124..85c3f56 100644
--- a/curve25519-dalek/build.rs
+++ b/curve25519-dalek/build.rs
@@ -12,6 +12,7 @@ enum DalekBits {
     Dalek64,
 }
 
+//TODO: remove debugging before merging
 macro_rules! build_debug {
     ($($tokens: tt)*) => {
         println!("cargo:warning={}", format!($($tokens)*))
@@ -71,7 +72,7 @@ fn main() {
             },
             //coprocessor for Precursor
             Ok("u32e_backend") => {
-                if curve25519_dalek_bits != DalekBits::Dalek64{
+                if curve25519_dalek_bits != DalekBits::Dalek32{
                     panic!("u32e_backend only supports 32 bit bits");
                 }
                 "u32e_backend"
@@ -85,6 +86,7 @@ fn main() {
                 },
             }
         };
+    build_debug!("CARGO_CFG_CURVE25519_DALEK_BACKEND: {:?}", std::env::var("CARGO_CFG_CURVE25519_DALEK_BACKEND").as_deref());
     build_debug!("curve25519_dalek_backend {:?}", curve25519_dalek_backend);
     println!("cargo:rustc-cfg=curve25519_dalek_backend=\"{curve25519_dalek_backend}\"");
 }
diff --git a/curve25519-dalek/src/field.rs b/curve25519-dalek/src/field.rs
index db65845..f9b192c 100644
--- a/curve25519-dalek/src/field.rs
+++ b/curve25519-dalek/src/field.rs
@@ -509,6 +509,7 @@ mod test {
     }
 
     #[test]
+    #[cfg(curve25519_dalek_backend = "u32e_backend")]
     fn make_vectors() {
         // reminder to self: to create just this vector, run
         // cargo test field::test::make_vectors
diff --git a/curve25519-dalek/src/lib.rs b/curve25519-dalek/src/lib.rs
index aa930a6..aded117 100644
--- a/curve25519-dalek/src/lib.rs
+++ b/curve25519-dalek/src/lib.rs
@@ -62,21 +62,12 @@ pub(crate) mod macros;
 
 //To consider upstreaming, we likely can't do this. Consider the "panic_on_sw_eval" feature
 #[allow(unused_imports)]
-#[cfg(any(test, curve25519_dalek_backend = "u32e_backend"))]
+#[cfg(curve25519_dalek_backend = "u32e_backend")]
 #[macro_use]
 extern crate engine25519_as;
-#[cfg(curve25519_dalek_backend = "u32e_backend")] //this is the binding for betrusted, so it should be gated 
-                                                  //with a "betrusted" flag, but we gate it with the backend 
-                                                  //flag for now. We'd need to refactor this to be
-                                                  //make it easier to support other platforms,
-                                                  //though there are no other platforms. For
-                                                  //upstreaming this might be diserable, but for
-                                                  //now, we'll leave it as a TODO.
+#[cfg(curve25519_dalek_backend = "u32e_backend")]
 extern crate engine_25519;
-
-#[cfg(curve25519_dalek_backend = "u32e_backend")] //while this is specific to betrusted, any other
-                                                  //use of this hardware would likely also need
-                                                  //utralib, at least that would be easiest.
+#[cfg(curve25519_dalek_backend = "u32e_backend")]
 extern crate utralib;
 
 //------------------------------------------------------------------------