More robust extension checking

Author: ChrisDenton

Diff for: std/src/sys/pal/windows/mod.rs

@@ -13,7 +13,7 @@ use crate::time::Duration;
 #[macro_use]
 pub mod compat;
 
-mod api;
+pub mod api;
 
 pub mod args;
 pub mod c;

Diff for: std/src/sys/pal/windows/process.rs

@@ -272,11 +272,24 @@ impl Command {
             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()?,

Diff for: std/src/sys/path/windows.rs

@@ -1,5 +1,6 @@
 use crate::ffi::{OsStr, OsString};
 use crate::path::{Path, PathBuf, Prefix};
+use crate::sys::api::utf16;
 use crate::sys::pal::{c, fill_utf16_buf, os2path, to_u16s};
 use crate::{io, ptr};
 
@@ -19,6 +20,10 @@ 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)