getWindows

pub fn getWindows(environ: Environ, key: [*:0]const u16) ?[:0]const u16 {
    // '=' anywhere but the start makes this an invalid environment variable name.
    const key_slice = mem.sliceTo(key, 0);
    if (key_slice.len == 0 or mem.findScalar(u16, key_slice[1..], '=') != null) return null;

    if (!environ.block.use_global) return null;

    const peb = std.os.windows.peb();
    assert(std.os.windows.ntdll.RtlEnterCriticalSection(peb.FastPebLock) == .SUCCESS);
    defer assert(std.os.windows.ntdll.RtlLeaveCriticalSection(peb.FastPebLock) == .SUCCESS);
    const ptr = peb.ProcessParameters.Environment;

    var i: usize = 0;
    while (ptr[i] != 0) {
        const key_value = mem.sliceTo(ptr[i..], 0);

        // There are some special environment variables that start with =,
        // so we need a special case to not treat = as a key/value separator
        // if it's the first character.
        // https://devblogs.microsoft.com/oldnewthing/20100506-00/?p=14133
        const equal_index = mem.findScalarPos(u16, key_value, 1, '=') orelse {
            // This is enforced by CreateProcess.
            // If violated, CreateProcess will fail with INVALID_PARAMETER.
            unreachable; // must contain a =
        };

        const this_key = key_value[0..equal_index];
        if (std.os.windows.eqlIgnoreCaseWtf16(key_slice, this_key)) {
            return key_value[equal_index + 1 ..];
        }

        // skip past the NUL terminator
        i += key_value.len + 1;
    }
    return null;
}