Auto merge of #13116 - tesuji:fix_zero_repeat_side_effects, r=y21

Lint `zero_repeat_side_effects`  only if array length is a literal zero

changelog: [`zero_repeat_side_effects` ] Lint only if array length is a literal zero
Fixes #13110 .
r? y21

clippy_lints/src/zero_repeat_side_effects.rs

@@ -3,10 +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::{ExprKind, Node};
+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;
 
@@ -45,18 +46,26 @@ declare_clippy_lint! {
 declare_lint_pass!(ZeroRepeatSideEffects => [ZERO_REPEAT_SIDE_EFFECTS]);
 
 impl LateLintPass<'_> for ZeroRepeatSideEffects {
-    fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'_ rustc_hir::Expr<'_>) {
+    fn check_expr(&mut self, cx: &LateContext<'_>, expr: &rustc_hir::Expr<'_>) {
+        let hir_map = cx.tcx.hir();
         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
+            && let LitKind::Int(Pu128(0), _) = l.node
-            && i.0 == 0
         {
             inner_check(cx, expr, inner_expr, true);
-        } else if let ExprKind::Repeat(inner_expr, _) = expr.kind
+        }
-            && let ty::Array(_, cst) = cx.typeck_results().expr_ty(expr).kind()
+        // Lint only if the length is a literal zero, and not a path to any constants.
-            && let ConstKind::Value(_, ty::ValTree::Leaf(element_count)) = cst.kind()
+        // NOTE(@y21): When reading `[f(); LEN]`, I intuitively expect that the function is called and it
-            && element_count.to_target_usize(cx.tcx) == 0
+        // 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];
@@ -58,3 +58,15 @@ fn main() {
     // as function param
     drop(vec![f(); 1]);
 }
+
+macro_rules! LEN {
+    () => {
+        0
+    };
+}
+
+fn issue_13110() {
+    let _data = [f(); LEN!()];
+    const LENGTH: usize = LEN!();
+    let _data = [f(); LENGTH];
+}

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];
@@ -58,3 +58,15 @@ fn main() {
     // as function param
     drop(vec![f(); 1]);
 }
+
+macro_rules! LEN {
+    () => {
+        0
+    };
+}
+
+fn issue_13110() {
+    let _data = [f(); LEN!()];
+    const LENGTH: usize = LEN!();
+    let _data = [f(); LENGTH];
+}

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
+  --> tests/ui/zero_repeat_side_effects.rs:20:5
-   |
-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
    |
 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
+  --> tests/ui/zero_repeat_side_effects.rs:24:5
-   |
-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
    |
 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
+error: aborting due to 9 previous errors
-  --> 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