Avoid divide-by-zero when checking if a field will merge with bitfields

src/codegen/struct_layout.rs

@@ -335,9 +335,12 @@ impl<'a> StructLayoutTracker<'a> {
             new_field_layout
         );
 
+        // Avoid divide-by-zero errors if align is 0.
+        let align = cmp::max(1, layout.align);
+
         if self.last_field_was_bitfield &&
-            new_field_layout.align <= layout.size % layout.align &&
-            new_field_layout.size <= layout.size % layout.align
+            new_field_layout.align <= layout.size % align &&
+            new_field_layout.size <= layout.size % align
         {
             // The new field will be coalesced into some of the remaining bits.
             //

tests/expectations/tests/divide-by-zero-in-struct-layout.rs

@@ -0,0 +1,45 @@
+/* automatically generated by rust-bindgen */
+
+
+#![allow(dead_code, non_snake_case, non_camel_case_types, non_upper_case_globals)]
+
+
+#[repr(C)]
+#[derive(Debug, Default, Copy, Clone)]
+pub struct WithBitfield {
+    pub _bitfield_1: [u8; 0usize],
+    pub __bindgen_padding_0: u32,
+    pub a: ::std::os::raw::c_uint,
+}
+impl WithBitfield {
+    #[inline]
+    pub fn new_bitfield_1() -> u8 {
+        0
+    }
+}
+#[repr(C, packed)]
+#[derive(Debug, Default, Copy, Clone)]
+pub struct WithBitfieldAndAttrPacked {
+    pub _bitfield_1: [u8; 0usize],
+    pub a: ::std::os::raw::c_uint,
+    pub __bindgen_padding_0: u8,
+}
+impl WithBitfieldAndAttrPacked {
+    #[inline]
+    pub fn new_bitfield_1() -> u8 {
+        0
+    }
+}
+#[repr(C, packed)]
+#[derive(Debug, Default, Copy, Clone)]
+pub struct WithBitfieldAndPacked {
+    pub _bitfield_1: [u8; 0usize],
+    pub a: ::std::os::raw::c_uint,
+    pub __bindgen_padding_0: u8,
+}
+impl WithBitfieldAndPacked {
+    #[inline]
+    pub fn new_bitfield_1() -> u8 {
+        0
+    }
+}

tests/headers/divide-by-zero-in-struct-layout.h

@@ -0,0 +1,22 @@
+// bindgen-flags: --no-layout-tests
+//
+// Unfortunately, we aren't translating the second and third structs correctly
+// yet. But we definitely shouldn't divide-by-zero when we see it...
+//
+// Once we fix #981 we should remove the `--no-layout-tests`.
+
+struct WithBitfield {
+    unsigned : 7;
+    unsigned a;
+};
+
+struct WithBitfieldAndAttrPacked {
+    unsigned : 7;
+    unsigned a;
+} __attribute__((packed));
+
+#pragma pack(1)
+struct WithBitfieldAndPacked {
+    unsigned : 7;
+    unsigned a;
+};