✨ Forbid zero sized type

src/lib.rs

@@ -125,6 +125,7 @@ use std::marker::PhantomData;
 pub use segment::Segment;
 pub use segment_builder::{DefaultSegmentBuilder, SegmentBuilder};
 pub use stats::MmapStats;
+use utils::check_zst;
 pub use vec_builder::MmapVecBuilder;
 
 #[cfg(feature = "serde")]
@@ -157,6 +158,8 @@ where
     /// Create a zero size mmap vec.
     #[inline(always)]
     pub fn new() -> Self {
+        check_zst::<T>();
+
         let builder = B::default();
         let path = builder.new_segment_path();
         Self {

src/segment.rs

@@ -10,7 +10,7 @@ use std::{
 
 use crate::{
     stats::{COUNT_ACTIVE_SEGMENT, COUNT_FTRUNCATE_FAILED, COUNT_MMAP_FAILED, COUNT_MUNMAP_FAILED},
-    utils::page_size,
+    utils::{check_zst, page_size},
 };
 
 /// Segment is a constant slice of type T that is memory mapped to disk.
@@ -29,6 +29,7 @@ impl<T> Segment<T> {
     /// Create a zero size segment.
     #[inline(always)]
     pub const fn null() -> Self {
+        check_zst::<T>();
         Self {
             addr: std::ptr::null_mut(),
             len: 0,
@@ -40,6 +41,7 @@ impl<T> Segment<T> {
     ///
     /// File will be created and init with computed capacity.
     pub fn open_rw<P: AsRef<Path>>(path: P, capacity: usize) -> io::Result<Self> {
+        check_zst::<T>();
         if capacity == 0 {
             return Ok(Self::null());
         }
@@ -284,6 +286,7 @@ unsafe impl<T> Send for Segment<T> {}
 unsafe impl<T> Sync for Segment<T> {}
 
 unsafe fn ftruncate<T>(file: &File, capacity: usize) -> io::Result<()> {
+    check_zst::<T>();
     let segment_size = capacity * mem::size_of::<T>();
     let fd = file.as_raw_fd();
 
@@ -296,6 +299,7 @@ unsafe fn ftruncate<T>(file: &File, capacity: usize) -> io::Result<()> {
 }
 
 unsafe fn mmap<T>(file: &File, capacity: usize) -> io::Result<*mut T> {
+    check_zst::<T>();
     let segment_size = capacity * mem::size_of::<T>();
 
     // It is safe to not keep a reference to the initial file descriptor.
@@ -321,6 +325,7 @@ unsafe fn mmap<T>(file: &File, capacity: usize) -> io::Result<*mut T> {
 }
 
 unsafe fn munmap<T>(addr: *mut T, capacity: usize) -> io::Result<()> {
+    check_zst::<T>();
     debug_assert!(!addr.is_null());
     debug_assert!(capacity > 0);
 

src/utils.rs

@@ -1,3 +1,11 @@
+use std::mem;
+
 pub fn page_size() -> usize {
     unsafe { libc::sysconf(libc::_SC_PAGESIZE) as usize }
 }
+
+pub const fn check_zst<T>() {
+    if mem::size_of::<T>() == 0 {
+        panic!("Zero sized type are not supported with MmapVec. What is the point of mapping ZST to disk ?");
+    }
+}

src/vec_builder.rs

@@ -1,6 +1,9 @@
 use std::{io, marker::PhantomData, mem};
 
-use crate::{utils::page_size, DefaultSegmentBuilder, MmapVec, Segment, SegmentBuilder};
+use crate::{
+    utils::{check_zst, page_size},
+    DefaultSegmentBuilder, MmapVec, Segment, SegmentBuilder,
+};
 
 /// Helps to create vec with custom parameters.
 ///
@@ -62,6 +65,7 @@ impl<T, SB: SegmentBuilder> MmapVecBuilder<T, SB> {
 impl<T, SB: SegmentBuilder> Default for MmapVecBuilder<T, SB> {
     #[inline(always)]
     fn default() -> Self {
+        check_zst::<T>();
         Self {
             segment_builder: SB::default(),
             capacity: page_size() / mem::size_of::<T>(),

tests/test_vec.rs

@@ -392,3 +392,11 @@ fn test_try_from_vec() {
     let vec = MmapVec::<_, DefaultSegmentBuilder>::try_from(Vec::from([8, 6, 4, -48, 16])).unwrap();
     assert_eq!(&vec[..], [8, 6, 4, -48, 16]);
 }
+
+#[test]
+#[should_panic = "Zero sized type are not supported"]
+fn test_zero_sized_type() {
+    struct VoidStruct;
+
+    let _vec = MmapVec::<VoidStruct>::with_capacity(50).unwrap();
+}