Let llvm tools auto-detect threads when not explicitly specified

When user doesn't pass --threads flag, avoid forcing --num-threads on llvm-profdata and llvm-cov to allow them to auto-detect optimal thread count.
Only pass --num-threads when user explicitly sets a value.

Author: asthetik

src/lib.rs

@@ -179,7 +179,7 @@ pub fn consumer(
     guess_directory: bool,
     binary_path: Option<&Path>,
     ignore_parsing_error: bool,
-    num_threads: usize,
+    llvm_threads: Option<usize>,
 ) {
     let mut gcov_type = GcovType::Unknown;
 
@@ -291,7 +291,7 @@ pub fn consumer(
                         profraw_paths.as_slice(),
                         binary_path.as_ref().unwrap(),
                         working_dir,
-                        num_threads,
+                        llvm_threads,
                     ) {
                         Ok(lcovs) => {
                             let mut new_results: Vec<(String, CovResult)> = Vec::new();

src/llvm_tools.rs

@@ -81,21 +81,25 @@ pub fn llvm_profiles_to_lcov(
     profile_paths: &[PathBuf],
     binary_path: &Path,
     working_dir: &Path,
-    num_threads: usize,
+    num_threads: Option<usize>,
 ) -> Result<Vec<Vec<u8>>, String> {
     let profdata_path = working_dir.join("grcov.profdata");
 
-    let num_threads = num_threads.to_string();
-    let args = vec![
+    let mut args = vec![
         "merge".as_ref(),
         "-f".as_ref(),
         "-".as_ref(),
         "-sparse".as_ref(),
         "-o".as_ref(),
         profdata_path.as_ref(),
-        "--num-threads".as_ref(),
-        num_threads.as_ref(),
     ];
+    let num_threads_str: String;
+    // Only pass --num-threads if explicitly specified by the user
+    if let Some(num) = num_threads {
+        num_threads_str = num.to_string();
+        args.push("--num-threads".as_ref());
+        args.push(num_threads_str.as_ref());
+    }
 
     let stdin_paths: String = profile_paths.iter().fold("".into(), |mut a, x| {
         a.push_str(x.to_string_lossy().as_ref());
@@ -111,14 +115,21 @@ pub fn llvm_profiles_to_lcov(
     let results = binaries
         .into_par_iter()
         .filter_map(|binary| {
-            let args = [
+            let mut args = vec![
                 "export".as_ref(),
                 binary.as_ref(),
                 "--instr-profile".as_ref(),
                 profdata_path.as_ref(),
                 "--format".as_ref(),
                 "lcov".as_ref(),
             ];
+            let num_threads_str: String;
+            // Only pass --num-threads if explicitly specified by the user
+            if let Some(num) = num_threads {
+                num_threads_str = num.to_string();
+                args.push("--num-threads".as_ref());
+                args.push(num_threads_str.as_ref());
+            }
 
             match run(&cov_tool_path, &args) {
                 Ok(result) => Some(result),
@@ -305,7 +316,7 @@ mod tests {
             &[tmp_path.join("default.profraw")],
             &PathBuf::from("src"), // There is no binary file in src
             tmp_path,
-            1,
+            None,
         );
         assert!(lcovs.is_ok());
         let lcovs = lcovs.unwrap();
@@ -322,7 +333,7 @@ mod tests {
             &[tmp_path.join("default.profraw")],
             &tmp_path.join(binary_path),
             tmp_path,
-            1,
+            None,
         );
         assert!(lcovs.is_ok(), "Error: {}", lcovs.unwrap_err());
         let lcovs = lcovs.unwrap();
@@ -355,8 +366,12 @@ mod tests {
 
         assert_eq!(status.unwrap().code().unwrap(), 0);
 
-        let lcovs =
-            llvm_profiles_to_lcov(&[profdata_path], &tmp_path.join(binary_path), tmp_path, 1);
+        let lcovs = llvm_profiles_to_lcov(
+            &[profdata_path],
+            &tmp_path.join(binary_path),
+            tmp_path,
+            None,
+        );
 
         assert!(lcovs.is_ok(), "Error: {}", lcovs.unwrap_err());
         let lcovs = lcovs.unwrap();
@@ -403,7 +418,7 @@ mod tests {
             &[path_with, path_without],
             &tmp_path.join(bin_path),
             tmp_path,
-            1,
+            None,
         );
 
         assert!(lcovs.is_ok(), "Error: {}", lcovs.unwrap_err());

src/main.rs

@@ -451,6 +451,7 @@ fn main() {
         let branch_enabled = opt.branch;
         let guess_directory = opt.guess_directory;
         let ignore_parsing_error = opt.ignore_parsing_error;
+        let llvm_threads = opt.threads;
 
         let t = thread::Builder::new()
             .name(format!("Consumer {i}"))
@@ -465,7 +466,7 @@ fn main() {
                     guess_directory,
                     binary_path.as_deref(),
                     ignore_parsing_error,
-                    num_threads,
+                    llvm_threads,
                 );
             })
             .unwrap();