Make cast_ptr_alignment ignore c_void

clippy_lints/src/types.rs

@@ -13,7 +13,7 @@ use syntax::ast::{FloatTy, IntTy, UintTy};
 use syntax::codemap::Span;
 use syntax::errors::DiagnosticBuilder;
 use utils::{comparisons, higher, in_constant, in_external_macro, in_macro, last_path_segment, match_def_path, match_path,
-            multispan_sugg, opt_def_id, same_tys, snippet, snippet_opt, span_help_and_lint, span_lint,
+            match_type, multispan_sugg, opt_def_id, same_tys, snippet, snippet_opt, span_help_and_lint, span_lint,
             span_lint_and_sugg, span_lint_and_then, clip, unsext, sext, int_bits};
 use utils::paths;
 use consts::{constant, Constant};
@@ -981,6 +981,11 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CastPass {
                 if let Some(from_align) = cx.layout_of(from_ptr_ty.ty).ok().map(|a| a.align.abi());
                 if let Some(to_align) = cx.layout_of(to_ptr_ty.ty).ok().map(|a| a.align.abi());
                 if from_align < to_align;
+                // with c_void, we inherently need to trust the user
+                if ! (
+                    match_type(cx, from_ptr_ty.ty, &paths::C_VOID)
+                    || match_type(cx, from_ptr_ty.ty, &paths::C_VOID_LIBC)
+                );
                 then {
                     span_lint(
                         cx,

clippy_lints/src/utils/paths.rs

@@ -20,6 +20,8 @@ pub const CMP_MAX: [&str; 3] = ["core", "cmp", "max"];
 pub const CMP_MIN: [&str; 3] = ["core", "cmp", "min"];
 pub const COW: [&str; 3] = ["alloc", "borrow", "Cow"];
 pub const CSTRING_NEW: [&str; 5] = ["std", "ffi", "c_str", "CString", "new"];
+pub const C_VOID: [&str; 4] = ["std", "os", "raw", "c_void"];
+pub const C_VOID_LIBC: [&str; 2] = ["libc", "c_void"];
 pub const DEBUG_FMT_METHOD: [&str; 4] = ["core", "fmt", "Debug", "fmt"];
 pub const DEFAULT_TRAIT: [&str; 3] = ["core", "default", "Default"];
 pub const DISPLAY_FMT_METHOD: [&str; 4] = ["core", "fmt", "Display", "fmt"];

tests/ui/cast_alignment.rs

@@ -1,5 +1,9 @@
 //! Test casts for alignment issues
 
+#![feature(libc)]
+
+extern crate libc;
+
 #[warn(cast_ptr_alignment)]
 #[allow(no_effect, unnecessary_operation, cast_lossless)]
 fn main() {
@@ -16,4 +20,7 @@ fn main() {
     // cast to less-strictly-aligned type
     (&1u16 as *const u16) as *const u8;
     (&mut 1u16 as *mut u16) as *mut u8;
+    // For c_void, we should trust the user. See #2677
+    (&1u32 as *const u32 as *const std::os::raw::c_void) as *const u32;
+    (&1u32 as *const u32 as *const libc::c_void) as *const u32;
 }

tests/ui/cast_alignment.stderr

@@ -1,15 +1,15 @@
 error: casting from `*const u8` to a more-strictly-aligned pointer (`*const u16`)
- --> $DIR/cast_alignment.rs:9:5
+  --> $DIR/cast_alignment.rs:13:5
    |
-9 |     (&1u8 as *const u8) as *const u16;
+13 |     (&1u8 as *const u8) as *const u16;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D cast-ptr-alignment` implied by `-D warnings`
 
 error: casting from `*mut u8` to a more-strictly-aligned pointer (`*mut u16`)
-  --> $DIR/cast_alignment.rs:10:5
+  --> $DIR/cast_alignment.rs:14:5
    |
-10 |     (&mut 1u8 as *mut u8) as *mut u16;
+14 |     (&mut 1u8 as *mut u8) as *mut u16;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 2 previous errors