Auto merge of #4816 - rust-lang:zst-offset, r=phansch

New lint: zst_offset

This fixes #4813

changelog: add `zst_offset` lint

Author: bors

CHANGELOG.md

@@ -1273,4 +1273,5 @@ Released 2018-09-13
 [`zero_prefixed_literal`]: https://rust-lang.github.io/rust-clippy/master/index.html#zero_prefixed_literal
 [`zero_ptr`]: https://rust-lang.github.io/rust-clippy/master/index.html#zero_ptr
 [`zero_width_space`]: https://rust-lang.github.io/rust-clippy/master/index.html#zero_width_space
+[`zst_offset`]: https://rust-lang.github.io/rust-clippy/master/index.html#zst_offset
 <!-- end autogenerated links to lint list -->

README.md

@@ -6,7 +6,7 @@
 
 A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
 
-[There are 333 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
+[There are 334 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
 
 We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
 

clippy_lints/src/lib.rs

@@ -624,6 +624,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         &methods::USELESS_ASREF,
         &methods::WRONG_PUB_SELF_CONVENTION,
         &methods::WRONG_SELF_CONVENTION,
+        &methods::ZST_OFFSET,
         &minmax::MIN_MAX,
         &misc::CMP_NAN,
         &misc::CMP_OWNED,
@@ -1176,6 +1177,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         LintId::of(&methods::UNNECESSARY_FOLD),
         LintId::of(&methods::USELESS_ASREF),
         LintId::of(&methods::WRONG_SELF_CONVENTION),
+        LintId::of(&methods::ZST_OFFSET),
         LintId::of(&minmax::MIN_MAX),
         LintId::of(&misc::CMP_NAN),
         LintId::of(&misc::CMP_OWNED),
@@ -1497,6 +1499,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         LintId::of(&methods::CLONE_DOUBLE_REF),
         LintId::of(&methods::TEMPORARY_CSTRING_AS_PTR),
         LintId::of(&methods::UNINIT_ASSUMED_INIT),
+        LintId::of(&methods::ZST_OFFSET),
         LintId::of(&minmax::MIN_MAX),
         LintId::of(&misc::CMP_NAN),
         LintId::of(&misc::FLOAT_CMP),

clippy_lints/src/methods/mod.rs

@@ -1065,6 +1065,23 @@ declare_clippy_lint! {
     "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
 }
 
+declare_clippy_lint! {
+    /// **What it does:** Checks for `offset(_)`, `wrapping_`{`add`, `sub`}, etc. on raw pointers to
+    /// zero-sized types
+    ///
+    /// **Why is this bad?** This is a no-op, and likely unintended
+    ///
+    /// **Known problems:** None
+    ///
+    /// **Example:**
+    /// ```ignore
+    /// unsafe { (&() as *const ()).offest(1) };
+    /// ```
+    pub ZST_OFFSET,
+    correctness,
+    "Check for offset calculations on raw pointers to zero-sized types"
+}
+
 declare_lint_pass!(Methods => [
     OPTION_UNWRAP_USED,
     RESULT_UNWRAP_USED,
@@ -1109,6 +1126,7 @@ declare_lint_pass!(Methods => [
     SUSPICIOUS_MAP,
     UNINIT_ASSUMED_INIT,
     MANUAL_SATURATING_ARITHMETIC,
+    ZST_OFFSET,
 ]);
 
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Methods {
@@ -1167,6 +1185,9 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Methods {
             | ["unwrap_or", arith @ "checked_mul"] => {
                 manual_saturating_arithmetic::lint(cx, expr, &arg_lists, &arith["checked_".len()..])
             },
+            ["add"] | ["offset"] | ["sub"] | ["wrapping_offset"] | ["wrapping_add"] | ["wrapping_sub"] => {
+                check_pointer_offset(cx, expr, arg_lists[0])
+            },
             _ => {},
         }
 
@@ -3063,3 +3084,15 @@ fn contains_return(expr: &hir::Expr) -> bool {
     visitor.visit_expr(expr);
     visitor.found
 }
+
+fn check_pointer_offset(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
+    if_chain! {
+        if args.len() == 2;
+        if let ty::RawPtr(ty::TypeAndMut { ref ty, .. }) = cx.tables.expr_ty(&args[0]).kind;
+        if let Ok(layout) = cx.tcx.layout_of(cx.param_env.and(ty));
+        if layout.is_zst();
+        then {
+            span_lint(cx, ZST_OFFSET, expr.span, "offset calculation on zero-sized value");
+        }
+    }
+}

src/lintlist/mod.rs

@@ -6,7 +6,7 @@ pub use lint::Lint;
 pub use lint::LINT_LEVELS;
 
 // begin lint list, do not remove this comment, it’s used in `update_lints`
-pub const ALL_LINTS: [Lint; 333] = [
+pub const ALL_LINTS: [Lint; 334] = [
     Lint {
         name: "absurd_extreme_comparisons",
         group: "correctness",
@@ -2338,5 +2338,12 @@ pub const ALL_LINTS: [Lint; 333] = [
         deprecation: None,
         module: "unicode",
     },
+    Lint {
+        name: "zst_offset",
+        group: "correctness",
+        desc: "Check for offset calculations on raw pointers to zero-sized types",
+        deprecation: None,
+        module: "methods",
+    },
 ];
 // end lint list, do not remove this comment, it’s used in `update_lints`

tests/ui/zero_offset.rs

@@ -0,0 +1,12 @@
+fn main() {
+    unsafe {
+        let x = &() as *const ();
+        x.offset(0);
+        x.wrapping_add(0);
+        x.sub(0);
+        x.wrapping_sub(0);
+
+        let y = &1 as *const u8;
+        y.offset(0);
+    }
+}

tests/ui/zero_offset.stderr

@@ -0,0 +1,9 @@
+error[E0606]: casting `&i32` as `*const u8` is invalid
+  --> $DIR/zero_offset.rs:9:17
+   |
+LL |         let y = &1 as *const u8;
+   |                 ^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0606`.