Include command stdout in error message (#1756)

* Include command stdout in error message

* On Windows pclose returns the exit code

mlx/backend/common/compiled_cpu.cpp

@@ -7,6 +7,8 @@
 #include <mutex>
 #include <shared_mutex>
 
+#include <fmt/format.h>
+
 #include "mlx/backend/common/compiled.h"
 #include "mlx/backend/common/compiled_preamble.h"
 #include "mlx/backend/common/jit_compiler.h"
@@ -105,14 +107,14 @@ void* compile(
     source_file << source_code;
     source_file.close();
 
-    std::string command = JitCompiler::build_command(
-        output_dir, source_file_name, shared_lib_name);
-    auto return_code = system(command.c_str());
-    if (return_code) {
-      std::ostringstream msg;
-      msg << "[Compile::eval_cpu] Failed to compile function " << kernel_name
-          << " with error code " << return_code << "." << std::endl;
-      throw std::runtime_error(msg.str());
+    try {
+      JitCompiler::exec(JitCompiler::build_command(
+          output_dir, source_file_name, shared_lib_name));
+    } catch (const std::exception& error) {
+      throw std::runtime_error(fmt::format(
+          "[Compile::eval_cpu] Failed to compile function {0}: {1}",
+          kernel_name,
+          error.what()));
     }
   }
 

mlx/backend/common/jit_compiler.cpp

@@ -24,29 +24,6 @@ std::vector<std::string> str_split(const std::string& str, char delimiter) {
   return tokens;
 }
 
-// Run a command and get its output.
-std::string exec(const std::string& cmd) {
-  std::unique_ptr<FILE, decltype(&_pclose)> pipe(
-      _popen(cmd.c_str(), "r"), _pclose);
-  if (!pipe) {
-    throw std::runtime_error("popen() failed.");
-  }
-  char buffer[128];
-  std::string ret;
-  while (fgets(buffer, sizeof(buffer), pipe.get())) {
-    ret += buffer;
-  }
-  // Trim trailing spaces.
-  ret.erase(
-      std::find_if(
-          ret.rbegin(),
-          ret.rend(),
-          [](unsigned char ch) { return !std::isspace(ch); })
-          .base(),
-      ret.end());
-  return ret;
-}
-
 // Get path information about MSVC.
 struct VisualStudioInfo {
   VisualStudioInfo() {
@@ -56,7 +33,7 @@ struct VisualStudioInfo {
     arch = "x64";
 #endif
     // Get path of Visual Studio.
-    std::string vs_path = exec(fmt::format(
+    std::string vs_path = JitCompiler::exec(fmt::format(
         "\"{0}\\Microsoft Visual Studio\\Installer\\vswhere.exe\""
         " -property installationPath",
         std::getenv("ProgramFiles(x86)")));
@@ -64,7 +41,7 @@ struct VisualStudioInfo {
       throw std::runtime_error("Can not find Visual Studio.");
     }
     // Read the envs from vcvarsall.
-    std::string envs = exec(fmt::format(
+    std::string envs = JitCompiler::exec(fmt::format(
         "\"{0}\\VC\\Auxiliary\\Build\\vcvarsall.bat\" {1} >NUL && set",
         vs_path,
         arch));
@@ -110,7 +87,7 @@ std::string JitCompiler::build_command(
       "\""
       "cd /D \"{0}\" && "
       "\"{1}\" /LD /EHsc /MD /Ox /nologo /std:c++17 \"{2}\" "
-      "/link /out:\"{3}\" {4} >nul"
+      "/link /out:\"{3}\" {4} 2>&1"
       "\"",
       dir.string(),
       info.cl_exe,
@@ -119,10 +96,57 @@ std::string JitCompiler::build_command(
       libpaths);
 #else
   return fmt::format(
-      "g++ -std=c++17 -O3 -Wall -fPIC -shared '{0}' -o '{1}'",
+      "g++ -std=c++17 -O3 -Wall -fPIC -shared '{0}' -o '{1}' 2>&1",
       (dir / source_file_name).string(),
       (dir / shared_lib_name).string());
 #endif
 }
 
+std::string JitCompiler::exec(const std::string& cmd) {
+#ifdef _MSC_VER
+  FILE* pipe = _popen(cmd.c_str(), "r");
+#else
+  FILE* pipe = popen(cmd.c_str(), "r");
+#endif
+  if (!pipe) {
+    throw std::runtime_error("popen() failed.");
+  }
+  char buffer[128];
+  std::string ret;
+  while (fgets(buffer, sizeof(buffer), pipe)) {
+    ret += buffer;
+  }
+  // Trim trailing spaces.
+  ret.erase(
+      std::find_if(
+          ret.rbegin(),
+          ret.rend(),
+          [](unsigned char ch) { return !std::isspace(ch); })
+          .base(),
+      ret.end());
+
+#ifdef _MSC_VER
+  int status = _pclose(pipe);
+#else
+  int status = pclose(pipe);
+#endif
+  if (status == -1) {
+    throw std::runtime_error("pclose() failed.");
+  }
+#ifdef _MSC_VER
+  int code = status;
+#else
+  int code = WEXITSTATUS(status);
+#endif
+  if (code != 0) {
+    throw std::runtime_error(fmt::format(
+        "Failed to execute command with return code {0}: \"{1}\", "
+        "the output is: {2}",
+        code,
+        cmd,
+        ret));
+  }
+  return ret;
+}
+
 } // namespace mlx::core

mlx/backend/common/jit_compiler.h

@@ -12,6 +12,9 @@ class JitCompiler {
       const std::filesystem::path& dir,
       const std::string& source_file_name,
       const std::string& shared_lib_name);
+
+  // Run a command and get its output.
+  static std::string exec(const std::string& cmd);
 };
 
 } // namespace mlx::core