work with nil returned by malloc for 0-sized arrays

Author: danielrh

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "alloc-no-stdlib"
 description = "A dynamic allocator that may be used with or without the stdlib. This allows a package with nostd to allocate memory dynamically and be used either with a custom allocator, items on the stack, or by a package that wishes to simply use Box<>. It also provides options to use calloc or a mutable global variable for pre-zeroed memory"
-version = "2.0.0"
+version = "2.0.1"
 authors = ["Daniel Reiter Horn <danielrh@dropbox.com>"]
 documentation = "https://raw.githubusercontent.com/dropbox/rust-alloc-no-stdlib/master/tests/lib.rs"
 homepage = "https://github.com/dropbox/rust-alloc-no-stdlib"

src/lib.rs

@@ -39,25 +39,34 @@ pub enum AllocatorC {
 }
 impl<'a, T : 'a> CallocBackingStore<'a, T> {
   pub unsafe fn new(num_elements : usize, alloc : AllocatorC, free : unsafe extern "C" fn (*mut u8), should_free : bool) -> Self{
-     let retval : *mut u8 = match alloc {
-          AllocatorC::Calloc(calloc) => calloc(num_elements, core::mem::size_of::<T>()),
-          AllocatorC::Malloc(malloc) => malloc(num_elements *core::mem::size_of::<T>()),
-          AllocatorC::Custom(malloc) => malloc(num_elements *core::mem::size_of::<T>()),
+     let retval : *mut u8 = if num_elements == 0 {core::ptr::null_mut()} else {
+        match alloc {
+           AllocatorC::Calloc(calloc) => calloc(num_elements, core::mem::size_of::<T>()),
+           AllocatorC::Malloc(malloc) => malloc(num_elements *core::mem::size_of::<T>()),
+           AllocatorC::Custom(malloc) => malloc(num_elements *core::mem::size_of::<T>()),
+        }
      };
+     if num_elements == 0 || retval.is_null() {
+        return CallocBackingStore::<'a, T>{
+         raw_data : core::ptr::null_mut(),
+         data : &mut[],
+         free : free,
+       }
+     }
      let raw_data : *mut T = core::mem::transmute(retval);
      if should_free {
        return CallocBackingStore::<'a, T>{
          raw_data : retval,
          data : core::slice::from_raw_parts_mut(raw_data,
-                                                           num_elements),
+                                                num_elements),
          free : free,
        };
      } else {
        let null_ptr : *const u8 = core::ptr::null();
        return CallocBackingStore::<'a, T>{
          raw_data : core::mem::transmute(null_ptr),//retval,
          data : core::slice::from_raw_parts_mut(raw_data,
-                                                           num_elements),
+                                                num_elements),
          free : free,
        };
     }