lib: remove usage of winreg crate

This pulls in a whole library just for what is morally 3 function calls
and can be done easily in the Windows API. Remove it.

This uses `unsafe`; the usage of `windows-rs` might be more preferrable
since we already (and will likely always) depend on it, but it would
probably remain unsafe...

Signed-off-by: Austin Seipp <aseipp@pobox.com>

Cargo.lock

@@ -2396,7 +2396,6 @@ dependencies = [
  "tracing",
  "version_check",
  "watchman_client",
- "winreg",
 ]
 
 [[package]]
@@ -4798,16 +4797,6 @@ dependencies = [
  "memchr",
 ]
 
-[[package]]
-name = "winreg"
-version = "0.52.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a277a57398d4bfa075df44f501a17cfdf8542d224f0d36095a2adc7aee4ef0a5"
-dependencies = [
- "cfg-if",
- "windows-sys 0.48.0",
-]
-
 [[package]]
 name = "wit-bindgen-rt"
 version = "0.39.0"

Cargo.toml

@@ -122,7 +122,6 @@ unicode-width = "0.2.0"
 version_check = "0.9.5"
 watchman_client = { version = "0.9.0" }
 whoami = "1.6.0"
-winreg = "0.52"
 
 # put all inter-workspace libraries, i.e. those that use 'path = ...' here in
 # their own (alphabetically sorted) block

lib/Cargo.toml

@@ -79,7 +79,6 @@ watchman_client = { workspace = true, optional = true }
 rustix = { workspace = true }
 
 [target.'cfg(windows)'.dependencies]
-winreg = { workspace = true }
 
 [dev-dependencies]
 assert_matches = { workspace = true }

lib/src/file_util.rs

@@ -180,20 +180,97 @@ mod platform {
 
 #[cfg(windows)]
 mod platform {
+    use std::ffi::c_void;
     use std::io;
+    use std::mem;
     use std::os::windows::fs::symlink_file;
     use std::path::Path;
+    use std::ptr;
 
-    use winreg::enums::HKEY_LOCAL_MACHINE;
-    use winreg::RegKey;
+    type HKEY = *mut c_void;
+    type LSTATUS = i32;
+    type DWORD = u32;
+    type REGSAM = u32;
+
+    const HKEY_LOCAL_MACHINE: HKEY = 0x80000002 as HKEY;
+    const KEY_READ: REGSAM = 0x20019;
+    const REG_DWORD: DWORD = 4;
+    const ERROR_SUCCESS: LSTATUS = 0;
+
+    #[link(name = "advapi32")]
+    extern "system" {
+        fn RegOpenKeyExA(
+            hKey: HKEY,
+            lpSubKey: *const u8,
+            ulOptions: DWORD,
+            samDesired: REGSAM,
+            phkResult: *mut HKEY,
+        ) -> LSTATUS;
+
+        fn RegQueryValueExA(
+            hKey: HKEY,
+            lpValueName: *const u8,
+            lpReserved: *mut DWORD,
+            lpType: *mut DWORD,
+            lpData: *mut u8,
+            lpcbData: *mut DWORD,
+        ) -> LSTATUS;
+
+        fn RegCloseKey(hKey: HKEY) -> LSTATUS;
+    }
 
     /// Symlinks may or may not be enabled on Windows. They require the
     /// Developer Mode setting, which is stored in the registry key below.
     pub fn check_symlink_support() -> io::Result<bool> {
-        let hklm = RegKey::predef(HKEY_LOCAL_MACHINE);
-        let sideloading =
-            hklm.open_subkey("SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\AppModelUnlock")?;
-        let developer_mode: u32 = sideloading.get_value("AllowDevelopmentWithoutDevLicense")?;
+        // Registry subkey containing the developer mode setting
+        let subkey = b"SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\AppModelUnlock\0";
+        // Value name for developer mode setting
+        let value_name = b"AllowDevelopmentWithoutDevLicense\0";
+
+        // Return value from registry operations
+        let mut key_handle: HKEY = ptr::null_mut();
+        let mut developer_mode: DWORD = 0;
+        let mut value_type: DWORD = 0;
+        let mut data_size: DWORD = mem::size_of::<DWORD>() as DWORD;
+
+        #[allow(unsafe_code)]
+        unsafe {
+            // Open the registry key
+            let result = RegOpenKeyExA(
+                HKEY_LOCAL_MACHINE,
+                subkey.as_ptr(),
+                0,
+                KEY_READ,
+                &mut key_handle,
+            );
+
+            if result != ERROR_SUCCESS {
+                return Err(io::Error::from_raw_os_error(result));
+            }
+
+            let result = RegQueryValueExA(
+                key_handle,
+                value_name.as_ptr(),
+                ptr::null_mut(),
+                &mut value_type,
+                &mut developer_mode as *mut DWORD as *mut u8,
+                &mut data_size,
+            );
+
+            RegCloseKey(key_handle);
+
+            if result != ERROR_SUCCESS {
+                return Err(io::Error::from_raw_os_error(result));
+            }
+
+            if value_type != REG_DWORD {
+                return Err(io::Error::new(
+                    io::ErrorKind::InvalidData,
+                    "Registry value is not a DWORD",
+                ));
+            }
+        }
+
         Ok(developer_mode == 1)
     }
 

lib/src/lib.rs

@@ -16,7 +16,7 @@
 
 #![warn(missing_docs)]
 #![deny(unused_must_use)]
-#![forbid(unsafe_code)]
+#![deny(unsafe_code)]
 
 // Needed so that proc macros can be used inside jj_lib and by external crates
 // that depend on it.