Expose Environment Variables during Build

src/project.rs

@@ -15,6 +15,10 @@ use std::{
 
 const DEFAULT_FUZZ_DIR: &str = "fuzz";
 
+/// The name of the environment variable that exposes the cargo fuzz manifest
+/// path during builds.
+const BUILD_ENV_MANIFEST_DIR: &str = "CARGO_FUZZ_MANIFEST";
+
 pub struct FuzzProject {
     /// The project with fuzz targets
     fuzz_dir: PathBuf,
@@ -320,6 +324,29 @@ impl FuzzProject {
         }
     }
 
+    // Helper function for `exec_build()` used to expose cargo-fuzz information
+    // via environment variables. Such environment variables can be used by fuzz
+    // target dependencies' build scripts to adjust its build settings based on
+    // these variables' values.
+    //
+    // This is called directly before the `cargo build ...` command is executed.
+    // The command is passed in as a mutable reference such that the subprocess'
+    // environment (not *this* process' environment) will have the environment
+    // variables set.
+    fn exec_build_expose_env(
+        &self,
+        cmd: &mut Command,
+        _mode: options::BuildMode,
+        _build: &options::BuildOptions,
+        _fuzz_target: Option<&str>,
+    ) -> Result<()> {
+        // expose the path to the cargo-fuzz manifest to the subprocess
+        let manifest_path = self.manifest_path();
+        cmd.env(BUILD_ENV_MANIFEST_DIR, manifest_path.as_os_str());
+
+        Ok(())
+    }
+
     pub fn exec_build(
         &self,
         mode: options::BuildMode,
@@ -342,6 +369,11 @@ impl FuzzProject {
             cmd.arg("--target-dir").arg(target_dir);
         }
 
+        // expose build information via environment variables, before executing
+        // the build command
+        self.exec_build_expose_env(&mut cmd, mode, build, fuzz_target)
+            .expect("Failed to set cargo-fuzz build environment variables.");
+
         let status = cmd
             .status()
             .with_context(|| format!("failed to execute: {:?}", cmd))?;