Eagerly close tempfile to fix #1082 (#1087)

src/tempfile.rs

@@ -69,8 +69,8 @@ impl NamedTempfile {
         &self.path
     }
 
-    pub(super) fn file(&self) -> &File {
-        self.file.as_ref().unwrap()
+    pub(super) fn take_file(&mut self) -> Option<File> {
+        self.file.take()
     }
 }
 

src/tool.rs

@@ -122,7 +122,7 @@ impl Tool {
                     .into(),
             })?;
 
-            let tmp =
+            let mut tmp =
                 NamedTempfile::new(&out_dir, "detect_compiler_family.c").map_err(|err| Error {
                     kind: ErrorKind::IOError,
                     message: format!(
@@ -132,8 +132,13 @@ impl Tool {
                     )
                     .into(),
                 })?;
-            tmp.file()
-                .write_all(include_bytes!("detect_compiler_family.c"))?;
+            let mut tmp_file = tmp.take_file().unwrap();
+            tmp_file.write_all(include_bytes!("detect_compiler_family.c"))?;
+            // Close the file handle *now*, otherwise the compiler may fail to open it on Windows
+            // (#1082). The file stays on disk and its path remains valid until `tmp` is dropped.
+            tmp_file.flush()?;
+            tmp_file.sync_data()?;
+            drop(tmp_file);
 
             let stdout = run_output(
                 Command::new(path).arg("-E").arg(tmp.path()),