Lint only if array length is a literal zero.

Author: tesuji

clippy_lints/src/zero_repeat_side_effects.rs

@@ -3,11 +3,11 @@ use clippy_utils::higher::VecArgs;
 use clippy_utils::source::snippet;
 use clippy_utils::visitors::for_each_expr_without_closures;
 use rustc_ast::LitKind;
+use rustc_data_structures::packed::Pu128;
 use rustc_errors::Applicability;
-use rustc_hir::def::{DefKind, Res};
-use rustc_hir::{ArrayLen, ExprKind, ItemKind, Node, QPath};
+use rustc_hir::{ArrayLen, ExprKind, Node};
 use rustc_lint::{LateContext, LateLintPass};
-use rustc_middle::ty::{self, ConstKind, Ty};
+use rustc_middle::ty::Ty;
 use rustc_session::declare_lint_pass;
 use rustc_span::Span;
 
@@ -51,39 +51,23 @@ impl LateLintPass<'_> for ZeroRepeatSideEffects {
         if let Some(args) = VecArgs::hir(cx, expr)
             && let VecArgs::Repeat(inner_expr, len) = args
             && let ExprKind::Lit(l) = len.kind
-            && let LitKind::Int(i, _) = l.node
-            && i.0 == 0
+            && let LitKind::Int(Pu128(0), _) = l.node
         {
             inner_check(cx, expr, inner_expr, true);
-        } else {
-            let ExprKind::Repeat(inner_expr, length) = expr.kind else {
-                return;
-            };
-            // Skip if the length is from a macro.
-            if let ArrayLen::Body(anon_const) = length {
-                let length_expr = hir_map.body(anon_const.body).value;
-                if !length_expr.span.eq_ctxt(expr.span) {
-                    return;
-                }
-
-                // Get the initialization span of a const item and compare it with the span at use-site.
-                if let ExprKind::Path(QPath::Resolved(None, path)) = length_expr.kind
-                    && let Res::Def(DefKind::Const, def_id) = path.res
-                    && let Some(def_id) = def_id.as_local()
-                    && let Node::Item(item) = cx.tcx.hir_node_by_def_id(def_id)
-                    && let ItemKind::Const(_ty, _, body_id) = item.kind
-                    && let init_span = hir_map.span_with_body(body_id.hir_id)
-                    && !init_span.eq_ctxt(length_expr.span)
-                {
-                    return;
-                }
-            }
-            if let ty::Array(_, cst) = cx.typeck_results().expr_ty(expr).kind()
-                && let ConstKind::Value(_, ty::ValTree::Leaf(element_count)) = cst.kind()
-                && element_count.to_target_usize(cx.tcx) == 0
-            {
-                inner_check(cx, expr, inner_expr, false);
-            }
+        }
+        // Lint only if the length is a literal zero, and not a path to any constants.
+        // NOTE(@y21): When reading `[f(); LEN]`, I intuitively expect that the function is called and it
+        // doesn't seem as confusing as `[f(); 0]`. It would also have false positives when eg.
+        // the const item depends on `#[cfg]s` and has different values in different compilation
+        // sessions).
+        else if let ExprKind::Repeat(inner_expr, length) = expr.kind
+            && let ArrayLen::Body(anon_const) = length
+            && let length_expr = hir_map.body(anon_const.body).value
+            && !length_expr.span.from_expansion()
+            && let ExprKind::Lit(literal) = length_expr.kind
+            && let LitKind::Int(Pu128(0), _) = literal.node
+        {
+            inner_check(cx, expr, inner_expr, false);
         }
     }
 }

tests/ui/zero_repeat_side_effects.fixed

@@ -16,10 +16,8 @@ fn main() {
 
     // on arrays
     f(); let a: [i32; 0] = [];
-    f(); let a: [i32; 0] = [];
     let mut b;
     f(); b = [] as [i32; 0];
-    f(); b = [] as [i32; 0];
 
     // on vecs
     // vecs dont support infering value of consts
@@ -39,9 +37,11 @@ fn main() {
     // when singled out/not part of assignment/local
     { f(); vec![] as std::vec::Vec<i32> };
     { f(); [] as [i32; 0] };
-    { f(); [] as [i32; 0] };
 
     // should not trigger
+    let a = [f(); N];
+    b = [f(); N];
+    [f(); N];
 
     // on arrays with > 0 repeat
     let a = [f(); 1];

tests/ui/zero_repeat_side_effects.rs

@@ -16,10 +16,8 @@ fn main() {
 
     // on arrays
     let a = [f(); 0];
-    let a = [f(); N];
     let mut b;
     b = [f(); 0];
-    b = [f(); N];
 
     // on vecs
     // vecs dont support infering value of consts
@@ -39,9 +37,11 @@ fn main() {
     // when singled out/not part of assignment/local
     vec![f(); 0];
     [f(); 0];
-    [f(); N];
 
     // should not trigger
+    let a = [f(); N];
+    b = [f(); N];
+    [f(); N];
 
     // on arrays with > 0 repeat
     let a = [f(); 1];

tests/ui/zero_repeat_side_effects.stderr

@@ -8,70 +8,52 @@ LL |     let a = [f(); 0];
    = help: to override `-D warnings` add `#[allow(clippy::zero_repeat_side_effects)]`
 
 error: function or method calls as the initial value in zero-sized array initializers may cause side effects
-  --> tests/ui/zero_repeat_side_effects.rs:19:5
-   |
-LL |     let a = [f(); N];
-   |     ^^^^^^^^^^^^^^^^^ help: consider using: `f(); let a: [i32; 0] = [];`
-
-error: function or method calls as the initial value in zero-sized array initializers may cause side effects
-  --> tests/ui/zero_repeat_side_effects.rs:21:5
+  --> tests/ui/zero_repeat_side_effects.rs:20:5
    |
 LL |     b = [f(); 0];
    |     ^^^^^^^^^^^^ help: consider using: `f(); b = [] as [i32; 0]`
 
 error: function or method calls as the initial value in zero-sized array initializers may cause side effects
-  --> tests/ui/zero_repeat_side_effects.rs:22:5
-   |
-LL |     b = [f(); N];
-   |     ^^^^^^^^^^^^ help: consider using: `f(); b = [] as [i32; 0]`
-
-error: function or method calls as the initial value in zero-sized array initializers may cause side effects
-  --> tests/ui/zero_repeat_side_effects.rs:26:5
+  --> tests/ui/zero_repeat_side_effects.rs:24:5
    |
 LL |     let c = vec![f(); 0];
    |     ^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f(); let c: std::vec::Vec<i32> = vec![];`
 
 error: function or method calls as the initial value in zero-sized array initializers may cause side effects
-  --> tests/ui/zero_repeat_side_effects.rs:28:5
+  --> tests/ui/zero_repeat_side_effects.rs:26:5
    |
 LL |     d = vec![f(); 0];
    |     ^^^^^^^^^^^^^^^^ help: consider using: `f(); d = vec![] as std::vec::Vec<i32>`
 
 error: function or method calls as the initial value in zero-sized array initializers may cause side effects
-  --> tests/ui/zero_repeat_side_effects.rs:31:5
+  --> tests/ui/zero_repeat_side_effects.rs:29:5
    |
 LL |     let e = [println!("side effect"); 0];
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `println!("side effect"); let e: [(); 0] = [];`
 
 error: function or method calls as the initial value in zero-sized array initializers may cause side effects
-  --> tests/ui/zero_repeat_side_effects.rs:34:5
+  --> tests/ui/zero_repeat_side_effects.rs:32:5
    |
 LL |     let g = [{ f() }; 0];
    |     ^^^^^^^^^^^^^^^^^^^^^ help: consider using: `{ f() }; let g: [i32; 0] = [];`
 
 error: function or method calls as the initial value in zero-sized array initializers may cause side effects
-  --> tests/ui/zero_repeat_side_effects.rs:37:10
+  --> tests/ui/zero_repeat_side_effects.rs:35:10
    |
 LL |     drop(vec![f(); 0]);
    |          ^^^^^^^^^^^^ help: consider using: `{ f(); vec![] as std::vec::Vec<i32> }`
 
 error: function or method calls as the initial value in zero-sized array initializers may cause side effects
-  --> tests/ui/zero_repeat_side_effects.rs:40:5
+  --> tests/ui/zero_repeat_side_effects.rs:38:5
    |
 LL |     vec![f(); 0];
    |     ^^^^^^^^^^^^ help: consider using: `{ f(); vec![] as std::vec::Vec<i32> }`
 
 error: function or method calls as the initial value in zero-sized array initializers may cause side effects
-  --> tests/ui/zero_repeat_side_effects.rs:41:5
+  --> tests/ui/zero_repeat_side_effects.rs:39:5
    |
 LL |     [f(); 0];
    |     ^^^^^^^^ help: consider using: `{ f(); [] as [i32; 0] }`
 
-error: function or method calls as the initial value in zero-sized array initializers may cause side effects
-  --> tests/ui/zero_repeat_side_effects.rs:42:5
-   |
-LL |     [f(); N];
-   |     ^^^^^^^^ help: consider using: `{ f(); [] as [i32; 0] }`
-
-error: aborting due to 12 previous errors
+error: aborting due to 9 previous errors