[pyth_oracle] Improve build.rs robustness and expose types. (#343)

* [pyth_oracle] robust build and library features

* precommit

---------

Co-authored-by: Jayant Krishnamurthy <jayantkrishnamurthy@gmail.com>

Author: Reisen

program/c/makefile

@@ -1,4 +1,6 @@
-OUT_DIR := ./target
+# Use the OUT_DIR env variable as the output directory if available, otherwise
+# default to ./target
+OUT_DIR := $(if $(OUT_DIR),$(OUT_DIR),./target)
 SOLANA := $(shell dirname $(shell which cargo-build-bpf))
 
 ifneq ("$(wildcard $(SOLANA)/sdk/bpf/c/bpf.mk)","")
@@ -9,11 +11,18 @@ else
   include $(SOLANA)/sdk/sbf/c/sbf.mk
 endif
 
+
+# Bundle C code compiled to bpf for use by rust
+.PHONY: cpyth-bpf
 cpyth-bpf:
-#   Bundle C code compiled to bpf for use by rust
-	bash -c "ar rcs target/libcpyth-bpf.a target/**/*.o"
+	bash -c "ar rcs $(OUT_DIR)/libcpyth-bpf.a target/**/*.o"
+
+
+# 2-Stage Contract Build
+#
+# 1) Compile C code to system architecture for use by rust's cargo test
+# 2) Bundle C code compiled to system architecture for use by rust's cargo test
+.PHONY: cpyth-native
 cpyth-native:
-#   Compile C code to system architecture for use by rust's cargo test
-	gcc -c ./src/oracle/native/upd_aggregate.c -o ./target/cpyth-native.o -fPIC
-#   Bundle C code compiled to system architecture for use by rust's cargo test
-	ar rcs target/libcpyth-native.a ./target/cpyth-native.o
+	gcc -c ./src/oracle/native/upd_aggregate.c -o $(OUT_DIR)/cpyth-native.o -fPIC
+	ar rcs $(OUT_DIR)/libcpyth-native.a $(OUT_DIR)/cpyth-native.o

program/rust/Cargo.toml

@@ -29,6 +29,7 @@ test-generator = "0.3.1"
 
 [features]
 debug = []
+library = []
 
 [lib]
 crate-type = ["cdylib", "lib"]

program/rust/build.rs

@@ -7,7 +7,33 @@ use {
 };
 
 fn main() {
-    println!("cargo:rustc-link-search=./program/c/target");
+    // Cargo exposes ENV variables for feature flags that can be used to determine whether to do a
+    // self-contained build that compiles the C components automatically.
+    if std::env::var("CARGO_FEATURE_LIBRARY").is_ok() {
+        // OUT_DIR is the path cargo provides to a build directory under `target/` specifically for
+        // isolated build artifacts. We use this to build the C program and then link against the
+        // resulting static library. This allows building the program when used as a dependency of
+        // another crate.
+        let out_dir = std::env::var("OUT_DIR").unwrap();
+        let out_dir = PathBuf::from(out_dir);
+
+        // We must forward OUT_DIR as an env variable to the make script otherwise it will output
+        // its artifacts to the wrong place.
+        std::process::Command::new("make")
+            .env("VERBOSE", "1")
+            .env("OUT_DIR", out_dir.display().to_string())
+            .current_dir("../c")
+            .args(["cpyth-native"])
+            .status()
+            .expect("Failed to build C program");
+
+        // Emit instructions for cargo to link against the built static library.
+        println!("cargo:rustc-link-lib=static=cpyth-native");
+        println!("cargo:rustc-link-search={}", out_dir.display());
+    } else {
+        // Otherwise fall back to the old relative-path C style build we used to have.
+        println!("cargo:rustc-link-search=./program/c/target");
+    }
 
     // Generate and write bindings
     let bindings = Builder::default()

program/rust/src/lib.rs

@@ -17,6 +17,25 @@ mod tests;
 #[cfg(feature = "debug")]
 mod log;
 
+// When compiled in `library` mode the on-chain definitions provided by this library are
+// exported. This is useful when other libraries wish to directly utilise the exact Solana specific
+// on-chain definitions of the Pyth program.
+//
+// While we have `pyth-sdk-rs` which exposes a more friendly interface, this is still useful when a
+// downstream user wants to confirm for example that they can compile against the binary interface
+// of this program for their specific solana version.
+#[cfg(feature = "library")]
+pub use accounts::{
+    AccountHeader,
+    MappingAccount,
+    PermissionAccount,
+    PriceAccount,
+    PriceComponent,
+    PriceEma,
+    PriceInfo,
+    ProductAccount,
+    PythAccount,
+};
 use {
     crate::error::OracleError,
     processor::process_instruction,