Revisiting indexing_slicing test cases

This commit contains a few changes. In an attempt to clarify which test cases should and should not produce stderr it became clear that some cases were being handled incorrectly. In order to address these test cases, a minor re-factor was made to the linting logic itself.

The re-factor was driven by edge case handling including a need for additional match conditions for `ExprCall` (`&x[0..=4]`) and `ExprBinary` (`x[1 << 3]`). Rather than attempt to account for each potential `Expr*` the code was re-factored into simply "if ranged index" and an "otherwise" conditions.

clippy_lints/src/indexing_slicing.rs

@@ -1,8 +1,9 @@
 //! lint on indexing and slicing operations
 
 use crate::consts::{constant, Constant};
+use crate::utils;
+use crate::utils::higher;
 use crate::utils::higher::Range;
-use crate::utils::{self, higher};
 use rustc::hir::*;
 use rustc::lint::*;
 use rustc::ty;
@@ -97,13 +98,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IndexingSlicing {
     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
         if let ExprIndex(ref array, ref index) = &expr.node {
             let ty = cx.tables.expr_ty(array);
-            match &index.node {
-                // Both ExprStruct and ExprPath require this approach's checks
-                // on the `range` returned by `higher::range(cx, index)`.
-                // ExprStruct handles &x[n..m], &x[n..] and &x[..n].
-                // ExprPath handles &x[..] and x[var]
-                ExprStruct(..) | ExprPath(..) => {
             if let Some(range) = higher::range(cx, index) {
+                // Ranged indexes, i.e. &x[n..m], &x[n..], &x[..n] and &x[..]
                 if let ty::TyArray(_, s) = ty.sty {
                     let size: u128 = s.assert_usize(cx.tcx).unwrap().into();
                     // Index is a constant range.
@@ -115,22 +111,15 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IndexingSlicing {
                                 expr.span,
                                 "range is out of bounds",
                             );
-                                } // Else range is in bounds, ok.
+                        }
-
                         return;
                     }
                 }
 
                 let help_msg = match (range.start, range.end) {
-                            (None, Some(_)) => {
+                    (None, Some(_)) => "Consider using `.get(..n)`or `.get_mut(..n)` instead",
-                                "Consider using `.get(..n)`or `.get_mut(..n)` instead"
+                    (Some(_), None) => "Consider using `.get(n..)` or .get_mut(n..)` instead",
-                            }
+                    (Some(_), Some(_)) => "Consider using `.get(n..m)` or `.get_mut(n..m)` instead",
-                            (Some(_), None) => {
-                                "Consider using `.get(n..)` or .get_mut(n..)` instead"
-                            }
-                            (Some(_), Some(_)) => {
-                                "Consider using `.get(n..m)` or `.get_mut(n..m)` instead"
-                            }
                     (None, None) => return, // [..] is ok.
                 };
 
@@ -142,23 +131,11 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IndexingSlicing {
                     help_msg,
                 );
             } else {
-                        utils::span_help_and_lint(
+                // Catchall non-range index, i.e. [n] or [n << m]
-                            cx,
-                            INDEXING_SLICING,
-                            expr.span,
-                            "indexing may panic.",
-                            "Consider using `.get(n)` or `.get_mut(n)` instead",
-                        );
-                    }
-                }
-                ExprLit(..) => {
-                    // [n]
                 if let ty::TyArray(_, s) = ty.sty {
                     let size: u128 = s.assert_usize(cx.tcx).unwrap().into();
                     // Index is a constant uint.
-                        if let Some((Constant::Int(const_index), _)) =
+                    if let Some((Constant::Int(const_index), _)) = constant(cx, cx.tables, index) {
-                            constant(cx, cx.tables, index)
-                        {
                         if size <= const_index {
                             utils::span_lint(
                                 cx,
@@ -168,8 +145,11 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IndexingSlicing {
                             );
                         }
                         // Else index is in bounds, ok.
+
+                        return;
                     }
-                    } else {
+                }
+
                 utils::span_help_and_lint(
                     cx,
                     INDEXING_SLICING,
@@ -179,9 +159,6 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IndexingSlicing {
                 );
             }
         }
-                _ => (),
-            }
-        }
     }
 }
 

tests/ui/indexing_slicing.rs

@@ -9,55 +9,63 @@ fn main() {
     let index_from: usize = 2;
     let index_to: usize = 3;
     x[index];
-    &x[index_from..index_to];
-    &x[index_from..][..index_to];
     &x[index..];
     &x[..index];
-    x[0];
+    &x[index_from..index_to];
-    x[3];
+    &x[index_from..][..index_to]; // Two lint reports, one for [index_from..] and another for [..index_to].
     x[4];
     x[1 << 3];
-    &x[1..5];
-    &x[1..][..5];
-    &x[0..3];
-    &x[0..][..3];
-    &x[0..].get(..3); // Ok
-    &x[0..=4];
     &x[..=4];
-    &x[..];
+    &x[1..5];
-    &x[1..];
+    &x[5..][..10]; // Two lint reports, one for [5..] and another for [..10].
-    &x[4..];
     &x[5..];
-    &x[..4];
     &x[..5];
     &x[5..].iter().map(|x| 2 * x).collect::<Vec<i32>>();
-    &x[2..].iter().map(|x| 2 * x).collect::<Vec<i32>>(); // Ok
+    &x[0..=4];
+    &x[0..][..3];
+    &x[1..][..5];
+
+    &x[4..]; // Ok, should not produce stderr.
+    &x[..4]; // Ok, should not produce stderr.
+    &x[..]; // Ok, should not produce stderr.
+    &x[1..]; // Ok, should not produce stderr.
+    &x[2..].iter().map(|x| 2 * x).collect::<Vec<i32>>(); // Ok, should not produce stderr.
+    &x[0..].get(..3); // Ok, should not produce stderr.
+    x[0]; // Ok, should not produce stderr.
+    x[3]; // Ok, should not produce stderr.
+    &x[0..3]; // Ok, should not produce stderr.
 
     let y = &x;
     y[0];
     &y[1..2];
-    &y[..];
     &y[0..=4];
     &y[..=4];
 
+    &y[..]; // Ok, should not produce stderr.
+
     let empty: [i8; 0] = [];
     empty[0];
     &empty[1..5];
     &empty[0..=4];
     &empty[..=4];
-    &empty[..];
-    &empty[0..];
-    &empty[0..0];
-    &empty[0..=0];
-    &empty[..=0];
-    &empty[..0];
     &empty[1..];
     &empty[..4];
+    &empty[0..=0];
+    &empty[..=0];
+
+    &empty[0..]; // Ok, should not produce stderr.
+    &empty[0..0]; // Ok, should not produce stderr.
+    &empty[..0]; // Ok, should not produce stderr.
+    &empty[..]; // Ok, should not produce stderr.
 
     let v = vec![0; 5];
     v[0];
     v[10];
+    v[1 << 3];
     &v[10..100];
+    &x[10..][..100]; // Two lint reports, one for [10..] and another for [..100].
     &v[10..];
     &v[..100];
+
+    &v[..]; // Ok, should not produce stderr.
 }

tests/ui/indexing_slicing.stderr

@@ -10,109 +10,135 @@ error: indexing may panic.
 error: slicing may panic.
   --> $DIR/indexing_slicing.rs:12:6
    |
-12 |     &x[index_from..index_to];
+12 |     &x[index..];
+   |      ^^^^^^^^^^
+   |
+   = help: Consider using `.get(n..)` or .get_mut(n..)` instead
+
+error: slicing may panic.
+  --> $DIR/indexing_slicing.rs:13:6
+   |
+13 |     &x[..index];
+   |      ^^^^^^^^^^
+   |
+   = help: Consider using `.get(..n)`or `.get_mut(..n)` instead
+
+error: slicing may panic.
+  --> $DIR/indexing_slicing.rs:14:6
+   |
+14 |     &x[index_from..index_to];
    |      ^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: Consider using `.get(n..m)` or `.get_mut(n..m)` instead
 
 error: slicing may panic.
-  --> $DIR/indexing_slicing.rs:13:6
+  --> $DIR/indexing_slicing.rs:15:6
    |
-13 |     &x[index_from..][..index_to];
+15 |     &x[index_from..][..index_to]; // Two lint reports, one for [index_from..] and another for [..index_to].
    |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: Consider using `.get(..n)`or `.get_mut(..n)` instead
 
 error: slicing may panic.
-  --> $DIR/indexing_slicing.rs:13:6
+  --> $DIR/indexing_slicing.rs:15:6
    |
-13 |     &x[index_from..][..index_to];
+15 |     &x[index_from..][..index_to]; // Two lint reports, one for [index_from..] and another for [..index_to].
    |      ^^^^^^^^^^^^^^^
    |
    = help: Consider using `.get(n..)` or .get_mut(n..)` instead
 
-error: slicing may panic.
-  --> $DIR/indexing_slicing.rs:14:6
-   |
-14 |     &x[index..];
-   |      ^^^^^^^^^^
-   |
-   = help: Consider using `.get(n..)` or .get_mut(n..)` instead
-
-error: slicing may panic.
-  --> $DIR/indexing_slicing.rs:15:6
-   |
-15 |     &x[..index];
-   |      ^^^^^^^^^^
-   |
-   = help: Consider using `.get(..n)`or `.get_mut(..n)` instead
-
 error: const index is out of bounds
-  --> $DIR/indexing_slicing.rs:18:5
+  --> $DIR/indexing_slicing.rs:16:5
    |
-18 |     x[4];
+16 |     x[4];
    |     ^^^^
    |
    = note: `-D out-of-bounds-indexing` implied by `-D warnings`
 
+error: const index is out of bounds
+  --> $DIR/indexing_slicing.rs:17:5
+   |
+17 |     x[1 << 3];
+   |     ^^^^^^^^^
+
+error: range is out of bounds
+  --> $DIR/indexing_slicing.rs:18:6
+   |
+18 |     &x[..=4];
+   |      ^^^^^^^
+
+error: range is out of bounds
+  --> $DIR/indexing_slicing.rs:19:6
+   |
+19 |     &x[1..5];
+   |      ^^^^^^^
+
+error: slicing may panic.
+  --> $DIR/indexing_slicing.rs:20:6
+   |
+20 |     &x[5..][..10]; // Two lint reports, one for [5..] and another for [..10].
+   |      ^^^^^^^^^^^^
+   |
+   = help: Consider using `.get(..n)`or `.get_mut(..n)` instead
+
 error: range is out of bounds
   --> $DIR/indexing_slicing.rs:20:6
    |
-20 |     &x[1..5];
+20 |     &x[5..][..10]; // Two lint reports, one for [5..] and another for [..10].
-   |      ^^^^^^^
+   |      ^^^^^^
 
-error: slicing may panic.
+error: range is out of bounds
   --> $DIR/indexing_slicing.rs:21:6
    |
-21 |     &x[1..][..5];
+21 |     &x[5..];
+   |      ^^^^^^
+
+error: range is out of bounds
+  --> $DIR/indexing_slicing.rs:22:6
+   |
+22 |     &x[..5];
+   |      ^^^^^^
+
+error: range is out of bounds
+  --> $DIR/indexing_slicing.rs:23:6
+   |
+23 |     &x[5..].iter().map(|x| 2 * x).collect::<Vec<i32>>();
+   |      ^^^^^^
+
+error: range is out of bounds
+  --> $DIR/indexing_slicing.rs:24:6
+   |
+24 |     &x[0..=4];
+   |      ^^^^^^^^
+
+error: slicing may panic.
+  --> $DIR/indexing_slicing.rs:25:6
+   |
+25 |     &x[0..][..3];
    |      ^^^^^^^^^^^
    |
    = help: Consider using `.get(..n)`or `.get_mut(..n)` instead
 
 error: slicing may panic.
-  --> $DIR/indexing_slicing.rs:23:6
+  --> $DIR/indexing_slicing.rs:26:6
    |
-23 |     &x[0..][..3];
+26 |     &x[1..][..5];
    |      ^^^^^^^^^^^
    |
    = help: Consider using `.get(..n)`or `.get_mut(..n)` instead
 
-error: range is out of bounds
-  --> $DIR/indexing_slicing.rs:26:6
-   |
-26 |     &x[..=4];
-   |      ^^^^^^^
-
-error: range is out of bounds
-  --> $DIR/indexing_slicing.rs:30:6
-   |
-30 |     &x[5..];
-   |      ^^^^^^
-
-error: range is out of bounds
-  --> $DIR/indexing_slicing.rs:32:6
-   |
-32 |     &x[..5];
-   |      ^^^^^^
-
-error: range is out of bounds
-  --> $DIR/indexing_slicing.rs:33:6
-   |
-33 |     &x[5..].iter().map(|x| 2 * x).collect::<Vec<i32>>();
-   |      ^^^^^^
-
 error: indexing may panic.
-  --> $DIR/indexing_slicing.rs:37:5
+  --> $DIR/indexing_slicing.rs:39:5
    |
-37 |     y[0];
+39 |     y[0];
    |     ^^^^
    |
    = help: Consider using `.get(n)` or `.get_mut(n)` instead
 
 error: slicing may panic.
-  --> $DIR/indexing_slicing.rs:38:6
+  --> $DIR/indexing_slicing.rs:40:6
    |
-38 |     &y[1..2];
+40 |     &y[1..2];
    |      ^^^^^^^
    |
    = help: Consider using `.get(n..m)` or `.get_mut(n..m)` instead
@@ -120,86 +146,128 @@ error: slicing may panic.
 error: slicing may panic.
   --> $DIR/indexing_slicing.rs:41:6
    |
-41 |     &y[..=4];
+41 |     &y[0..=4];
+   |      ^^^^^^^^
+   |
+   = help: Consider using `.get(n..m)` or `.get_mut(n..m)` instead
+
+error: slicing may panic.
+  --> $DIR/indexing_slicing.rs:42:6
+   |
+42 |     &y[..=4];
    |      ^^^^^^^
    |
    = help: Consider using `.get(..n)`or `.get_mut(..n)` instead
 
 error: const index is out of bounds
-  --> $DIR/indexing_slicing.rs:44:5
+  --> $DIR/indexing_slicing.rs:47:5
    |
-44 |     empty[0];
+47 |     empty[0];
    |     ^^^^^^^^
 
 error: range is out of bounds
-  --> $DIR/indexing_slicing.rs:45:6
+  --> $DIR/indexing_slicing.rs:48:6
    |
-45 |     &empty[1..5];
+48 |     &empty[1..5];
    |      ^^^^^^^^^^^
 
 error: range is out of bounds
-  --> $DIR/indexing_slicing.rs:47:6
+  --> $DIR/indexing_slicing.rs:49:6
    |
-47 |     &empty[..=4];
+49 |     &empty[0..=4];
+   |      ^^^^^^^^^^^^
+
+error: range is out of bounds
+  --> $DIR/indexing_slicing.rs:50:6
+   |
+50 |     &empty[..=4];
    |      ^^^^^^^^^^^
 
+error: range is out of bounds
+  --> $DIR/indexing_slicing.rs:51:6
+   |
+51 |     &empty[1..];
+   |      ^^^^^^^^^^
+
 error: range is out of bounds
   --> $DIR/indexing_slicing.rs:52:6
    |
-52 |     &empty[..=0];
+52 |     &empty[..4];
-   |      ^^^^^^^^^^^
+   |      ^^^^^^^^^^
+
+error: range is out of bounds
+  --> $DIR/indexing_slicing.rs:53:6
+   |
+53 |     &empty[0..=0];
+   |      ^^^^^^^^^^^^
 
 error: range is out of bounds
   --> $DIR/indexing_slicing.rs:54:6
    |
-54 |     &empty[1..];
+54 |     &empty[..=0];
-   |      ^^^^^^^^^^
+   |      ^^^^^^^^^^^
-
-error: range is out of bounds
-  --> $DIR/indexing_slicing.rs:55:6
-   |
-55 |     &empty[..4];
-   |      ^^^^^^^^^^
 
 error: indexing may panic.
-  --> $DIR/indexing_slicing.rs:58:5
+  --> $DIR/indexing_slicing.rs:62:5
    |
-58 |     v[0];
+62 |     v[0];
    |     ^^^^
    |
    = help: Consider using `.get(n)` or `.get_mut(n)` instead
 
 error: indexing may panic.
-  --> $DIR/indexing_slicing.rs:59:5
+  --> $DIR/indexing_slicing.rs:63:5
    |
-59 |     v[10];
+63 |     v[10];
    |     ^^^^^
    |
    = help: Consider using `.get(n)` or `.get_mut(n)` instead
 
-error: slicing may panic.
+error: indexing may panic.
-  --> $DIR/indexing_slicing.rs:60:6
+  --> $DIR/indexing_slicing.rs:64:5
    |
-60 |     &v[10..100];
+64 |     v[1 << 3];
+   |     ^^^^^^^^^
+   |
+   = help: Consider using `.get(n)` or `.get_mut(n)` instead
+
+error: slicing may panic.
+  --> $DIR/indexing_slicing.rs:65:6
+   |
+65 |     &v[10..100];
    |      ^^^^^^^^^^
    |
    = help: Consider using `.get(n..m)` or `.get_mut(n..m)` instead
 
 error: slicing may panic.
-  --> $DIR/indexing_slicing.rs:61:6
+  --> $DIR/indexing_slicing.rs:66:6
    |
-61 |     &v[10..];
+66 |     &x[10..][..100]; // Two lint reports, one for [10..] and another for [..100].
+   |      ^^^^^^^^^^^^^^
+   |
+   = help: Consider using `.get(..n)`or `.get_mut(..n)` instead
+
+error: range is out of bounds
+  --> $DIR/indexing_slicing.rs:66:6
+   |
+66 |     &x[10..][..100]; // Two lint reports, one for [10..] and another for [..100].
+   |      ^^^^^^^
+
+error: slicing may panic.
+  --> $DIR/indexing_slicing.rs:67:6
+   |
+67 |     &v[10..];
    |      ^^^^^^^
    |
    = help: Consider using `.get(n..)` or .get_mut(n..)` instead
 
 error: slicing may panic.
-  --> $DIR/indexing_slicing.rs:62:6
+  --> $DIR/indexing_slicing.rs:68:6
    |
-62 |     &v[..100];
+68 |     &v[..100];
    |      ^^^^^^^^
    |
    = help: Consider using `.get(..n)`or `.get_mut(..n)` instead
 
-error: aborting due to 28 previous errors
+error: aborting due to 38 previous errors