fix: Use nul instead of NUL on Windows

`NULL_DEVICE` is `/dev/null` except on Windows, where there are
several possible choices. Previously we were using `NUL` because
the more modern full path `\\.\NUL` is not supported by `git`.

However, `git` also rejects `NUL`, when capitalized, on some
Windows systems. This can be observed on Windows 11 ARM64 builds.
In contrast, the lower-case `nul`, which Windows itself treats the
same as `NUL`, is always accepted by Git for Windows.

This change allows some broken functionality to work on ARM64
Windows systems.

Author: EliahKagan

gix-path/src/env/git/mod.rs

@@ -84,8 +84,12 @@ pub(super) const EXE_NAME: &str = "git";
 /// The git executable is the one found in PATH or an alternative location.
 pub(super) static GIT_HIGHEST_SCOPE_CONFIG_PATH: Lazy<Option<BString>> = Lazy::new(exe_info);
 
+// There are a number of ways to refer to the null device on Windows, but they are not all equally
+// well supported. Git for Windows rejects `\\.\NUL` and `\\.\nul`. On Windows 11 ARM64 (and maybe
+// some others), it rejects even the legacy name `NUL`, when capitalized. But it always accepts the
+// lower-case `nul`, handling it in various path checks, some of which are done case-insensitively.
 #[cfg(windows)]
-const NULL_DEVICE: &str = "NUL";
+const NULL_DEVICE: &str = "nul";
 #[cfg(not(windows))]
 const NULL_DEVICE: &str = "/dev/null";
 

tests/tools/src/lib.rs

@@ -619,7 +619,7 @@ fn scripted_fixture_read_only_with_args_inner(
 }
 
 #[cfg(windows)]
-const NULL_DEVICE: &str = "NUL";
+const NULL_DEVICE: &str = "nul"; // See `gix_path::env::git::NULL_DEVICE` on why this form is used.
 #[cfg(not(windows))]
 const NULL_DEVICE: &str = "/dev/null";