Support array indexing expressions in unused write to a constant

clippy_lints/src/lib.rs

@@ -20,6 +20,7 @@
 #![warn(rust_2018_idioms, trivial_casts, trivial_numeric_casts)]
 #![feature(crate_visibility_modifier)]
 #![feature(try_from)]
+#![feature(if_while_or_patterns)]
 
 // FIXME: switch to something more ergonomic here, once available.
 // (currently there is no way to opt into sysroot crates w/o `extern crate`)

clippy_lints/src/no_effect.rs

@@ -101,7 +101,7 @@ fn has_no_effect(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
         ExprKind::Assign(ref left, ref right) => {
             if has_no_effect(cx, left) {
                 let mut left = left;
-                while let ExprKind::Field(f, _) = &left.node {
+                while let ExprKind::Field(f, _) | ExprKind::Index(f, _) = &left.node {
                     left = f;
                 }
                 if let ExprKind::Path(qpath) = &left.node {

tests/ui/no_effect.rs

@@ -74,9 +74,13 @@ struct B {
 struct C {
     b: B,
 }
+struct D {
+    arr: [i32; 1],
+}
 const A_CONST: A = A(1);
 const B: B = B { field: 1 };
 const C: C = C { b: B { field: 1 } };
+const D: D = D { arr: [1] };
 
 fn main() {
     let s = get_struct();
@@ -113,6 +117,7 @@ fn main() {
     A_CONST.0 = 2;
     B.field = 2;
     C.b.field = 2;
+    D.arr[0] = 2;
 
     // Do not warn
     get_number();
@@ -128,4 +133,6 @@ fn main() {
     b_mut.field = 2;
     let mut c_mut = C { b: B { field: 1 } };
     c_mut.b.field = 2;
+    let mut d_mut = D { arr: [1] };
+    d_mut.arr[0] = 2;
 }

tests/ui/no_effect.stderr

@@ -1,5 +1,5 @@
 error: statement with no effect
-  --> $DIR/no_effect.rs:85:5
+  --> $DIR/no_effect.rs:89:5
    |
 LL |     0;
    |     ^^
@@ -7,166 +7,172 @@ LL |     0;
    = note: `-D clippy::no-effect` implied by `-D warnings`
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:86:5
+  --> $DIR/no_effect.rs:90:5
    |
 LL |     s2;
    |     ^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:87:5
+  --> $DIR/no_effect.rs:91:5
    |
 LL |     Unit;
    |     ^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:88:5
+  --> $DIR/no_effect.rs:92:5
    |
 LL |     Tuple(0);
    |     ^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:89:5
+  --> $DIR/no_effect.rs:93:5
    |
 LL |     Struct { field: 0 };
    |     ^^^^^^^^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:90:5
+  --> $DIR/no_effect.rs:94:5
    |
 LL |     Struct { ..s };
    |     ^^^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:91:5
+  --> $DIR/no_effect.rs:95:5
    |
 LL |     Union { a: 0 };
    |     ^^^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:92:5
+  --> $DIR/no_effect.rs:96:5
    |
 LL |     Enum::Tuple(0);
    |     ^^^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:93:5
+  --> $DIR/no_effect.rs:97:5
    |
 LL |     Enum::Struct { field: 0 };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:94:5
+  --> $DIR/no_effect.rs:98:5
    |
 LL |     5 + 6;
    |     ^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:95:5
+  --> $DIR/no_effect.rs:99:5
    |
 LL |     *&42;
    |     ^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:96:5
+  --> $DIR/no_effect.rs:100:5
    |
 LL |     &6;
    |     ^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:97:5
+  --> $DIR/no_effect.rs:101:5
    |
 LL |     (5, 6, 7);
    |     ^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:98:5
+  --> $DIR/no_effect.rs:102:5
    |
 LL |     box 42;
    |     ^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:99:5
+  --> $DIR/no_effect.rs:103:5
    |
 LL |     ..;
    |     ^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:100:5
+  --> $DIR/no_effect.rs:104:5
    |
 LL |     5..;
    |     ^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:101:5
+  --> $DIR/no_effect.rs:105:5
    |
 LL |     ..5;
    |     ^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:102:5
+  --> $DIR/no_effect.rs:106:5
    |
 LL |     5..6;
    |     ^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:104:5
+  --> $DIR/no_effect.rs:108:5
    |
 LL |     [42, 55];
    |     ^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:105:5
+  --> $DIR/no_effect.rs:109:5
    |
 LL |     [42, 55][1];
    |     ^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:106:5
+  --> $DIR/no_effect.rs:110:5
    |
 LL |     (42, 55).1;
    |     ^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:107:5
+  --> $DIR/no_effect.rs:111:5
    |
 LL |     [42; 55];
    |     ^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:108:5
+  --> $DIR/no_effect.rs:112:5
    |
 LL |     [42; 55][13];
    |     ^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:110:5
+  --> $DIR/no_effect.rs:114:5
    |
 LL |     || x += 5;
    |     ^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:112:5
+  --> $DIR/no_effect.rs:116:5
    |
 LL |     FooString { s: s };
    |     ^^^^^^^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:113:5
+  --> $DIR/no_effect.rs:117:5
    |
 LL |     A_CONST.0 = 2;
    |     ^^^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:114:5
+  --> $DIR/no_effect.rs:118:5
    |
 LL |     B.field = 2;
    |     ^^^^^^^^^^^^
 
 error: statement with no effect
-  --> $DIR/no_effect.rs:115:5
+  --> $DIR/no_effect.rs:119:5
    |
 LL |     C.b.field = 2;
    |     ^^^^^^^^^^^^^^
 
-error: aborting due to 28 previous errors
+error: statement with no effect
+  --> $DIR/no_effect.rs:120:5
+   |
+LL |     D.arr[0] = 2;
+   |     ^^^^^^^^^^^^^
+
+error: aborting due to 29 previous errors