More robust extension checking

library/std/src/sys/pal/windows/mod.rs

@@ -14,7 +14,7 @@
 #[macro_use]
 pub mod compat;
 
-mod api;
+pub mod api;
 
 pub mod alloc;
 pub mod args;

library/std/src/sys/pal/windows/process.rs

@@ -279,11 +279,24 @@ pub fn spawn(
             None
         };
         let program = resolve_exe(&self.program, || env::var_os("PATH"), child_paths)?;
-        // Case insensitive "ends_with" of UTF-16 encoded ".bat" or ".cmd"
-        let is_batch_file = matches!(
-            program.len().checked_sub(5).and_then(|i| program.get(i..)),
-            Some([46, 98 | 66, 97 | 65, 116 | 84, 0] | [46, 99 | 67, 109 | 77, 100 | 68, 0])
-        );
+        let has_bat_extension = |program: &[u16]| {
+            matches!(
+                // Case insensitive "ends_with" of UTF-16 encoded ".bat" or ".cmd"
+                program.len().checked_sub(4).and_then(|i| program.get(i..)),
+                Some([46, 98 | 66, 97 | 65, 116 | 84] | [46, 99 | 67, 109 | 77, 100 | 68])
+            )
+        };
+        let is_batch_file = if path::is_verbatim(&program) {
+            has_bat_extension(&program[..program.len() - 1])
+        } else {
+            super::fill_utf16_buf(
+                |buffer, size| unsafe {
+                    // resolve the path so we can test the final file name.
+                    c::GetFullPathNameW(program.as_ptr(), size, buffer, ptr::null_mut())
+                },
+                |program| has_bat_extension(program),
+            )?
+        };
         let (program, mut cmd_str) = if is_batch_file {
             (
                 command_prompt()?,

library/std/src/sys/path/windows.rs

@@ -2,6 +2,7 @@
 use crate::io;
 use crate::path::{Path, PathBuf, Prefix};
 use crate::ptr;
+use crate::sys::api::utf16;
 use crate::sys::pal::{c, fill_utf16_buf, os2path, to_u16s};
 
 #[cfg(test)]
@@ -20,6 +21,10 @@ pub fn is_verbatim_sep(b: u8) -> bool {
     b == b'\\'
 }
 
+pub fn is_verbatim(path: &[u16]) -> bool {
+    path.starts_with(utf16!(r"\\?\")) || path.starts_with(utf16!(r"\??\"))
+}
+
 /// Returns true if `path` looks like a lone filename.
 pub(crate) fn is_file_name(path: &OsStr) -> bool {
     !path.as_encoded_bytes().iter().copied().any(is_sep_byte)

tests/ui/std/windows-bat-args.rs

@@ -32,7 +32,9 @@ fn parent() {
     let bat2 = String::from(bat.to_str().unwrap());
     bat.set_file_name("windows-bat-args3.bat");
     let bat3 = String::from(bat.to_str().unwrap());
-    let bat = [bat1.as_str(), bat2.as_str(), bat3.as_str()];
+    bat.set_file_name("windows-bat-args1.bat .. ");
+    let bat4 = String::from(bat.to_str().unwrap());
+    let bat = [bat1.as_str(), bat2.as_str(), bat3.as_str(), bat4.as_str()];
 
     check_args(&bat, &["a", "b"]).unwrap();
     check_args(&bat, &["c is for cat", "d is for dog"]).unwrap();