Merge pull request #509 from mcarton/array-indexing

Implement #364

README.md

@@ -6,7 +6,7 @@ A collection of lints to catch common mistakes and improve your Rust code.
 [Jump to usage instructions](#usage)
 
 ##Lints
-There are 84 lints included in this crate:
+There are 85 lints included in this crate:
 
 name                                                                                                     | default | meaning
 ---------------------------------------------------------------------------------------------------------|---------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
@@ -58,6 +58,7 @@ name
 [option_map_unwrap_or](https://github.com/Manishearth/rust-clippy/wiki#option_map_unwrap_or)             | warn    | using `Option.map(f).unwrap_or(a)`, which is more succinctly expressed as `map_or(a, f)`)
 [option_map_unwrap_or_else](https://github.com/Manishearth/rust-clippy/wiki#option_map_unwrap_or_else)   | warn    | using `Option.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `map_or_else(g, f)`)
 [option_unwrap_used](https://github.com/Manishearth/rust-clippy/wiki#option_unwrap_used)                 | allow   | using `Option.unwrap()`, which should at least get a better message using `expect()`
+[out_of_bounds_indexing](https://github.com/Manishearth/rust-clippy/wiki#out_of_bounds_indexing)         | deny    | out of bound constant indexing
 [precedence](https://github.com/Manishearth/rust-clippy/wiki#precedence)                                 | warn    | catches operations where precedence may be unclear. See the wiki for a list of cases caught
 [ptr_arg](https://github.com/Manishearth/rust-clippy/wiki#ptr_arg)                                       | warn    | fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` instead, respectively
 [range_step_by_zero](https://github.com/Manishearth/rust-clippy/wiki#range_step_by_zero)                 | warn    | using Range::step_by(0), which produces an infinite iterator

src/array_indexing.rs

@@ -0,0 +1,52 @@
+use rustc::lint::*;
+use rustc::middle::const_eval::EvalHint::ExprTypeChecked;
+use rustc::middle::const_eval::{eval_const_expr_partial, ConstVal};
+use rustc::middle::ty::TyArray;
+use rustc_front::hir::*;
+use utils::span_lint;
+
+/// **What it does:** Check for out of bounds array indexing with a constant index.
+///
+/// **Why is this bad?** This will always panic at runtime.
+///
+/// **Known problems:** Hopefully none.
+///
+/// **Example:**
+///
+/// ```
+/// let x = [1,2,3,4];
+/// ...
+/// x[9];
+/// ```
+declare_lint! {
+    pub OUT_OF_BOUNDS_INDEXING,
+    Deny,
+    "out of bound constant indexing"
+}
+
+#[derive(Copy,Clone)]
+pub struct ArrayIndexing;
+
+impl LintPass for ArrayIndexing {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(OUT_OF_BOUNDS_INDEXING)
+    }
+}
+
+impl LateLintPass for ArrayIndexing {
+    fn check_expr(&mut self, cx: &LateContext, e: &Expr) {
+        if let ExprIndex(ref array, ref index) = e.node {
+            let ty = cx.tcx.expr_ty(array);
+
+            if let TyArray(_, size) = ty.sty {
+                let index = eval_const_expr_partial(cx.tcx, &index, ExprTypeChecked, None);
+                if let Ok(ConstVal::Uint(index)) = index {
+                    if size as u64 <= index {
+                        span_lint(cx, OUT_OF_BOUNDS_INDEXING, e.span,
+                                  "const index-expr is out of bounds");
+                    }
+                }
+            }
+        }
+    }
+}

src/lib.rs

@@ -66,6 +66,7 @@ pub mod transmute;
 pub mod cyclomatic_complexity;
 pub mod escape;
 pub mod misc_early;
+pub mod array_indexing;
 
 mod reexport {
     pub use syntax::ast::{Name, NodeId};
@@ -121,6 +122,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
     reg.register_late_lint_pass(box escape::EscapePass);
     reg.register_early_lint_pass(box misc_early::MiscEarly);
     reg.register_late_lint_pass(box misc::UsedUnderscoreBinding);
+    reg.register_late_lint_pass(box array_indexing::ArrayIndexing);
 
     reg.register_lint_group("clippy_pedantic", vec![
         methods::OPTION_UNWRAP_USED,
@@ -143,6 +145,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
 
     reg.register_lint_group("clippy", vec![
         approx_const::APPROX_CONSTANT,
+        array_indexing::OUT_OF_BOUNDS_INDEXING,
         attrs::INLINE_ALWAYS,
         bit_mask::BAD_BIT_MASK,
         bit_mask::INEFFECTIVE_BIT_MASK,

tests/compile-fail/array_indexing.rs

@@ -0,0 +1,12 @@
+#![feature(plugin)]
+#![plugin(clippy)]
+
+#![deny(out_of_bounds_indexing)]
+
+fn main() {
+    let x = [1,2,3,4];
+    x[0];
+    x[3];
+    x[4]; //~ERROR: const index-expr is out of bounds
+    x[1 << 3]; //~ERROR: const index-expr is out of bounds
+}