Expose Environment Variables during Build

src/project.rs

@@ -15,6 +15,14 @@ use std::{
 
 const DEFAULT_FUZZ_DIR: &str = "fuzz";
 
+/// The name of the environment variable that is exposed to indicate a
+/// cargo-fuzz build is occurring.
+const BUILD_ENV_FLAG: &str = "CARGO_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 +328,39 @@ 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 detect whether or not cargo-fuzz is
+    // responsible for the build.
+    //
+    // This is called directly before the `cargo build ...` command is executed.
+    fn build_env_expose(
+        &self,
+        _mode: options::BuildMode,
+        _build: &options::BuildOptions,
+        _fuzz_target: Option<&str>,
+    ) -> Result<()> {
+        // expose a flag environment variable to allow the detection of cargo-fuzz
+        env::set_var(BUILD_ENV_FLAG, "1");
+
+        // expose the path to the cargo-fuzz manifest
+        let manifest_path = self.manifest_path();
+        env::set_var(BUILD_ENV_MANIFEST_DIR, manifest_path.as_os_str());
+
+        Ok(())
+    }
+
+    // Helper function for `exec_build()` used to un-expose cargo-fuzz
+    // information that was previously exposed in environment variables during
+    // `build_env_expose()`.
+    //
+    // This is called directly after the `cargo build ...` command is executed.
+    fn build_env_unexpose(&self) -> Result<()> {
+        env::remove_var(BUILD_ENV_FLAG);
+        env::remove_var(BUILD_ENV_MANIFEST_DIR);
+        Ok(())
+    }
+
     pub fn exec_build(
         &self,
         mode: options::BuildMode,
@@ -342,13 +383,22 @@ impl FuzzProject {
             cmd.arg("--target-dir").arg(target_dir);
         }
 
+        // expose build information via environment variables, before executing
+        // the build command
+        self.build_env_expose(mode, build, fuzz_target)
+            .expect("Failed to set cargo-fuzz build environment variables.");
+
         let status = cmd
             .status()
             .with_context(|| format!("failed to execute: {:?}", cmd))?;
         if !status.success() {
             bail!("failed to build fuzz script: {:?}", cmd);
         }
 
+        // un-expose build information, after the command has finished
+        self.build_env_unexpose()
+            .expect("Failed to un-set cargo-fuzz build environment variables.");
+
         Ok(())
     }