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src/project.rs

@@ -266,36 +266,27 @@ impl FuzzProject {
         Ok(cmd)
     }
 
-    fn target_dir(&self, build: &options::BuildOptions) -> Result<PathBuf> {
-        if build.coverage {
-            Ok(env::current_dir()?
-                .join("target")
-                .join(default_target())
-                .join("coverage"))
+    // note: never returns Ok(None) if build.coverage is true
+    fn target_dir(&self, build: &options::BuildOptions) -> Result<Option<PathBuf>> {
+        // Use the user-provided target directory, if provided. Otherwise if building for coverage,
+        // use the coverage directory
+        if let Some(target_dir) = build.target_dir.as_ref() {
+            return Ok(Some(PathBuf::from(target_dir)));
+        } else if build.coverage {
+            // To ensure that fuzzing and coverage-output generation can run in parallel, we
+            // produce a separate binary for the coverage command.
+            let current_dir = env::current_dir()?;
+            Ok(Some(
+                current_dir
+                    .join("target")
+                    .join(default_target())
+                    .join("coverage"),
+            ))
         } else {
-            Ok(build
-                .target_dir
-                .as_ref()
-                .map(PathBuf::from)
-                .unwrap_or_else(|| self.project_dir.join("target")))
+            Ok(None)
         }
     }
 
-    fn cargo_build_bin_path(
-        &self,
-        build: &options::BuildOptions,
-        fuzz_target: &str,
-    ) -> Result<PathBuf> {
-        let profile_subdir = if build.dev { "debug" } else { "release" };
-
-        let bin_path = self
-            .target_dir(&build)?
-            .join(&build.triple)
-            .join(profile_subdir)
-            .join(fuzz_target);
-        Ok(bin_path)
-    }
-
     pub fn exec_build(
         &self,
         mode: options::BuildMode,
@@ -314,8 +305,7 @@ impl FuzzProject {
             cmd.arg("--bins");
         }
 
-        if build.target_dir.is_some() || build.coverage {
-            let target_dir = self.target_dir(&build)?;
+        if let Some(target_dir) = self.target_dir(&build)? {
             cmd.arg("--target-dir").arg(target_dir);
         }
 
@@ -710,7 +700,23 @@ impl FuzzProject {
         coverage_dir: &Path,
         input_file: &Path,
     ) -> Result<(Command, String)> {
-        let mut cmd = Command::new(self.cargo_build_bin_path(&coverage.build, &coverage.target)?);
+        let bin_path = {
+            let profile_subdir = if coverage.build.dev {
+                "debug"
+            } else {
+                "release"
+            };
+
+            let target_dir = self
+                .target_dir(&coverage.build)?
+                .expect("target dir for coverage command should never be None");
+            target_dir
+                .join(&coverage.build.triple)
+                .join(profile_subdir)
+                .join(&coverage.target)
+        };
+
+        let mut cmd = Command::new(bin_path);
 
         // Raw coverage data will be saved in `coverage/<target>` directory.
         let input_file_name = input_file