feat(dfir_lang): support graph_ids #[no_std] via std, alloc, serde features (#2923)

Add `std`/`alloc`/`serde` feature flags. The only non-codegen module
(`graph_ids`) now compiles on bare-metal targets with zero std
dependencies.

- Add `#![cfg_attr(not(feature = "std"), no_std)]` to `lib.rs`
- Make `serde` optional (only needed for `slotmap` key serialization,
  pulled in by `codegen` feature)
- Set `slotmap` to `default-features = false`
- `codegen` feature implies `std` + `serde`

Co-authored-by: Infinity 🤖 <infinity@hydro.run>

Co-authored-by: Infinity 🤖 <infinity@hydro.run>

Author: MingweiSamuel

dfir_lang/Cargo.toml

@@ -12,8 +12,13 @@ license = { workspace = true }
 workspace = true
 
 [features]
-default = ["codegen"]
+default = ["std", "codegen"]
+std = ["alloc", "serde?/std", "slotmap/std"]
+alloc = ["serde?/alloc"]
+serde = ["dep:serde", "slotmap/serde"]
 codegen = [
+    "std",
+    "serde",
     "dep:auto_impl",
     "dep:documented",
     "dep:itertools",
@@ -38,9 +43,9 @@ itertools = { version = "0.14.0", optional = true }
 prettyplease = { version = "0.2.0", features = [ "verbatim" ], optional = true }
 proc-macro2 = { version = "1.0.95", features = [ "span-locations" ], optional = true }
 quote = { version = "1.0.35", optional = true }
-serde = "1.0.197"
+serde = { version = "1.0.197", default-features = false, optional = true }
 serde_json = { version = "1.0.115", optional = true }
-slotmap = { version = "1.1.0", features = ["serde"] }
+slotmap = { version = "1.1.0", default-features = false }
 syn = { version = "2.0.46", features = [ "extra-traits", "full", "parsing", "visit-mut" ], optional = true }
 webbrowser = { version = "1.0.3", optional = true }
 

dfir_lang/src/lib.rs

@@ -1,8 +1,13 @@
 //! DFIR syntax
-
+#![cfg_attr(not(feature = "std"), no_std)]
 #![warn(missing_docs)]
 #![cfg_attr(all(nightly, feature = "codegen"), feature(proc_macro_diagnostic))]
 
+#[cfg(any(test, feature = "alloc"))]
+extern crate alloc;
+#[cfg(any(test, feature = "std"))]
+extern crate std;
+
 pub mod graph_ids;
 
 #[cfg(feature = "codegen")]