Provide opt-out source compilation by feature `from_source

Co-authored-by: sagudev <16504129+sagudev@users.noreply.github.com>
Co-authored-by: Oliver Schneider <oli-obk@users.noreply.github.com>

README.md

@@ -75,22 +75,8 @@ fn main() {
 
 ## Note about serde_derive Binary
 
-When using `serde_derive` either directly or via `serde` with `derive` feature.
-
-Please note that `serde_derive` may be distributed from within pre-compiled binary
-
-To force building `serde_derive` from source, an override is provided:
-
-```sh
-RUSTFLAGS='--cfg serde_derive_build="source"'
-```
-
-Alternatively in `~/.cargo/config`:
-```toml
-rustflags = ['--cfg serde_derive_build="source"']
-```
-
-More info from [cargo reference](https://doc.rust-lang.org/cargo/reference/config.html#buildrustflags).
+To force building `serde_derive` from source, an override is provided via
+feature `from_source` if the target environment requires it.
 
 ## Getting help
 

precompiled/serde_derive/Cargo.toml

@@ -17,11 +17,19 @@ rust-version = "1.56"
 [features]
 default = []
 deserialize_in_place = []
+from_source = ["proc-macro2", "quote", "syn"]
 
 [lib]
 proc-macro = true
 
-[target.'cfg(any(serde_derive_build = "source", not(all(target_arch = "x86_64", target_os = "linux", target_env = "gnu"))))'.dependencies]
+# By feature source compilation
+[dependencies]
+proc-macro2 = { version = "1", optional = true }
+quote = { version = "1", optional = true }
+syn = { version = "2.0.28", optional = true }
+
+# Compile from source when no precompiled binary available
+[target.'cfg(not(all(target_arch = "x86_64", target_os = "linux", target_env = "gnu")))'.dependencies]
 proc-macro2 = "1"
 quote = "1"
 syn = "2.0.28"

precompiled/serde_derive/src/lib.rs

@@ -16,13 +16,13 @@
 #![doc(html_root_url = "https://docs.rs/serde_derive/1.0.183")]
 
 #[cfg(any(
-    serde_derive_build = "source",
+    feature = "from_source",
     not(all(target_arch = "x86_64", target_os = "linux", target_env = "gnu"))
 ))]
 include!("lib_from_source.rs");
 
 #[cfg(all(
-    not(serde_derive_build = "source"),
+    not(feature = "from_source"),
     target_arch = "x86_64",
     target_os = "linux",
     target_env = "gnu"

serde/Cargo.toml

@@ -40,6 +40,9 @@ default = ["std"]
 # Provide derive(Serialize, Deserialize) macros.
 derive = ["serde_derive"]
 
+# Force compilation from source - currently serde_derive
+from_source = ["serde_derive/from_source"]
+
 # Provide impls for common standard library types like Vec<T> and HashMap<K, V>.
 # Requires a dependency on the Rust standard library.
 std = []

serde_derive/Cargo.toml

@@ -14,6 +14,7 @@ rust-version = "1.56"
 
 [features]
 default = []
+from_source = []
 deserialize_in_place = []
 
 [lib]