stop warning never-returning calls

and add more test cases

Author: J-ZhengLi

clippy_lints/src/loops/infinite_loops.rs

@@ -1,52 +1,64 @@
 use clippy_utils::diagnostics::span_lint_and_then;
-use clippy_utils::is_lint_allowed;
+use clippy_utils::{fn_def_id, is_lint_allowed};
 use hir::intravisit::{walk_expr, Visitor};
-use hir::{Block, Destination, Expr, ExprKind, FnRetTy, Ty, TyKind};
+use hir::{Expr, ExprKind, FnRetTy, FnSig, Node};
 use rustc_ast::Label;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_lint::LateContext;
 
 use super::INFINITE_LOOPS;
 
-pub(super) fn check(
-    cx: &LateContext<'_>,
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
     expr: &Expr<'_>,
-    loop_block: &Block<'_>,
+    loop_block: &'tcx hir::Block<'_>,
     label: Option<Label>,
-    parent_fn_ret_ty: FnRetTy<'_>,
 ) {
-    if is_lint_allowed(cx, INFINITE_LOOPS, expr.hir_id)
-        || matches!(
-            parent_fn_ret_ty,
-            FnRetTy::Return(Ty {
-                kind: TyKind::Never,
-                ..
-            })
-        )
-    {
+    if is_lint_allowed(cx, INFINITE_LOOPS, expr.hir_id) {
+        return;
+    }
+
+    // Skip check if this loop is not in a function/method/closure. (In some weird case)
+    let Some(parent_fn_ret) = get_parent_fn_ret_ty(cx, expr) else {
+        return;
+    };
+    // Or, its parent function is already returning `Never`
+    if matches!(
+        parent_fn_ret,
+        FnRetTy::Return(hir::Ty {
+            kind: hir::TyKind::Never,
+            ..
+        })
+    ) {
         return;
     }
 
     // First, find any `break` or `return` without entering any inner loop,
     // then, find `return` or labeled `break` which breaks this loop with entering inner loop,
     // otherwise this loop is a infinite loop.
-    let mut direct_br_or_ret_finder = BreakOrRetFinder::default();
-    direct_br_or_ret_finder.visit_block(loop_block);
+    let mut direct_visitor = LoopVisitor {
+        cx,
+        label,
+        is_finite: false,
+        enter_nested_loop: false,
+    };
+    direct_visitor.visit_block(loop_block);
 
-    let is_finite_loop = direct_br_or_ret_finder.found || {
-        let mut inner_br_or_ret_finder = BreakOrRetFinder {
+    let is_finite_loop = direct_visitor.is_finite || {
+        let mut inner_loop_visitor = LoopVisitor {
+            cx,
             label,
+            is_finite: false,
             enter_nested_loop: true,
-            ..Default::default()
         };
-        inner_br_or_ret_finder.visit_block(loop_block);
-        inner_br_or_ret_finder.found
+        inner_loop_visitor.visit_block(loop_block);
+        inner_loop_visitor.is_finite
     };
 
     if !is_finite_loop {
         span_lint_and_then(cx, INFINITE_LOOPS, expr.span, "infinite loop detected", |diag| {
-            if let FnRetTy::DefaultReturn(ret_span) = parent_fn_ret_ty {
+            if let FnRetTy::DefaultReturn(ret_span) = parent_fn_ret {
                 diag.span_suggestion(
                     ret_span,
                     "if this is intentional, consider specifing `!` as function return",
@@ -56,37 +68,72 @@ pub(super) fn check(
             } else {
                 diag.span_help(
                     expr.span,
-                    "if this is not intended, add a `break` or `return` condition in this loop",
+                    "if this is not intended, try adding a `break` or `return` condition in this loop",
                 );
             }
         });
     }
 }
 
-#[derive(Default)]
-struct BreakOrRetFinder {
+fn get_parent_fn_ret_ty<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>) -> Option<FnRetTy<'tcx>> {
+    for (_, parent_node) in cx.tcx.hir().parent_iter(expr.hir_id) {
+        match parent_node {
+            Node::Item(hir::Item {
+                kind: hir::ItemKind::Fn(FnSig { decl, .. }, _, _),
+                ..
+            })
+            | Node::TraitItem(hir::TraitItem {
+                kind: hir::TraitItemKind::Fn(FnSig { decl, .. }, _),
+                ..
+            })
+            | Node::ImplItem(hir::ImplItem {
+                kind: hir::ImplItemKind::Fn(FnSig { decl, .. }, _),
+                ..
+            })
+            | Node::Expr(Expr {
+                kind: ExprKind::Closure(hir::Closure { fn_decl: decl, .. }),
+                ..
+            }) => return Some(decl.output),
+            _ => (),
+        }
+    }
+    None
+}
+
+struct LoopVisitor<'hir, 'tcx> {
+    cx: &'hir LateContext<'tcx>,
     label: Option<Label>,
-    found: bool,
+    is_finite: bool,
     enter_nested_loop: bool,
 }
 
-impl<'hir> Visitor<'hir> for BreakOrRetFinder {
+impl<'hir> Visitor<'hir> for LoopVisitor<'hir, '_> {
     fn visit_expr(&mut self, ex: &'hir Expr<'_>) {
         match &ex.kind {
-            ExprKind::Break(Destination { label, .. }, ..) => {
+            ExprKind::Break(hir::Destination { label, .. }, ..) => {
                 // When entering nested loop, only by breaking this loop's label
                 // would be considered as exiting this loop.
                 if self.enter_nested_loop {
                     if label.is_some() && *label == self.label {
-                        self.found = true;
+                        self.is_finite = true;
                     }
                 } else {
-                    self.found = true;
+                    self.is_finite = true;
                 }
             },
-            ExprKind::Ret(..) => self.found = true,
+            ExprKind::Ret(..) => self.is_finite = true,
             ExprKind::Loop(..) if !self.enter_nested_loop => (),
-            _ => walk_expr(self, ex),
+            _ => {
+                // Calls to a function that never return
+                if let Some(did) = fn_def_id(self.cx, ex) {
+                    let fn_ret_ty = self.cx.tcx.fn_sig(did).skip_binder().output().skip_binder();
+                    if fn_ret_ty.is_never() {
+                        self.is_finite = true;
+                        return;
+                    }
+                }
+                walk_expr(self, ex);
+            },
         }
     }
 }

clippy_lints/src/loops/mod.rs

@@ -23,7 +23,7 @@ mod while_let_on_iterator;
 
 use clippy_config::msrvs::Msrv;
 use clippy_utils::higher;
-use rustc_hir::{self as hir, Expr, ExprKind, LoopSource, Pat};
+use rustc_hir::{Expr, ExprKind, LoopSource, Pat};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::source_map::Span;
@@ -678,22 +678,20 @@ declare_clippy_lint! {
     "possibly unintended infinite loops"
 }
 
-pub struct Loops<'tcx> {
+pub struct Loops {
     msrv: Msrv,
     enforce_iter_loop_reborrow: bool,
-    parent_fn_ret_ty: Option<hir::FnRetTy<'tcx>>,
 }
-impl<'tcx> Loops<'tcx> {
+impl Loops {
     pub fn new(msrv: Msrv, enforce_iter_loop_reborrow: bool) -> Self {
         Self {
             msrv,
             enforce_iter_loop_reborrow,
-            parent_fn_ret_ty: None,
         }
     }
 }
 
-impl_lint_pass!(Loops<'_> => [
+impl_lint_pass!(Loops => [
     MANUAL_MEMCPY,
     MANUAL_FLATTEN,
     NEEDLESS_RANGE_LOOP,
@@ -717,7 +715,7 @@ impl_lint_pass!(Loops<'_> => [
     INFINITE_LOOPS,
 ]);
 
-impl<'tcx> LateLintPass<'tcx> for Loops<'tcx> {
+impl<'tcx> LateLintPass<'tcx> for Loops {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         let for_loop = higher::ForLoop::hir(expr);
         if let Some(higher::ForLoop {
@@ -757,9 +755,7 @@ impl<'tcx> LateLintPass<'tcx> for Loops<'tcx> {
             // also check for empty `loop {}` statements, skipping those in #[panic_handler]
             empty_loop::check(cx, expr, block);
             while_let_loop::check(cx, expr, block);
-            if let Some(parent_fn_ret_ty) = self.parent_fn_ret_ty {
-                infinite_loops::check(cx, expr, block, label, parent_fn_ret_ty);
-            }
+            infinite_loops::check(cx, expr, block, label);
         }
 
         while_let_on_iterator::check(cx, expr);
@@ -771,25 +767,11 @@ impl<'tcx> LateLintPass<'tcx> for Loops<'tcx> {
         }
     }
 
-    fn check_fn(
-        &mut self,
-        _: &LateContext<'tcx>,
-        kind: hir::intravisit::FnKind<'tcx>,
-        decl: &'tcx hir::FnDecl<'tcx>,
-        _: &'tcx hir::Body<'tcx>,
-        _: Span,
-        _: rustc_span::def_id::LocalDefId,
-    ) {
-        if let hir::intravisit::FnKind::ItemFn(..) = kind {
-            self.parent_fn_ret_ty = Some(decl.output);
-        }
-    }
-
     extract_msrv_attr!(LateContext);
 }
 
-impl<'tcx> Loops<'tcx> {
-    fn check_for_loop(
+impl Loops {
+    fn check_for_loop<'tcx>(
         &self,
         cx: &LateContext<'tcx>,
         pat: &'tcx Pat<'_>,

tests/ui/infinite_loops.rs

@@ -11,6 +11,31 @@ fn no_break() {
     }
 }
 
+fn all_inf() {
+    loop {
+        //~^ ERROR: infinite loop detected
+        loop {
+            //~^ ERROR: infinite loop detected
+            loop {
+                //~^ ERROR: infinite loop detected
+                do_something();
+            }
+        }
+        do_something();
+    }
+}
+
+fn no_break_return_some_ty() -> Option<u8> {
+    loop {
+        do_something();
+        return None;
+    }
+    loop {
+        //~^ ERROR: infinite loop detected
+        do_something();
+    }
+}
+
 fn no_break_never_ret() -> ! {
     loop {
         do_something();
@@ -256,4 +281,80 @@ fn ret_in_macro(opt: Option<u8>) {
     }
 }
 
+fn panic_like_macros_1() {
+    loop {
+        do_something();
+        panic!();
+    }
+}
+
+fn panic_like_macros_2() {
+    let mut x = 0;
+
+    loop {
+        do_something();
+        if true {
+            todo!();
+        }
+    }
+    loop {
+        do_something();
+        x += 1;
+        assert_eq!(x, 0);
+    }
+    loop {
+        do_something();
+        assert!(x % 2 == 0);
+    }
+    loop {
+        do_something();
+        match Some(1) {
+            Some(n) => println!("{n}"),
+            None => unreachable!("It won't happen"),
+        }
+    }
+}
+
+fn exit_directly(cond: bool) {
+    loop {
+        if cond {
+            std::process::exit(0);
+        }
+    }
+}
+
+trait MyTrait {
+    fn problematic_trait_method() {
+        loop {
+            //~^ ERROR: infinite loop detected
+            do_something();
+        }
+    }
+    fn could_be_problematic();
+}
+
+impl MyTrait for String {
+    fn could_be_problematic() {
+        loop {
+            //~^ ERROR: infinite loop detected
+            do_something();
+        }
+    }
+}
+
+fn inf_loop_in_closure() {
+    let _loop_forever = || {
+        loop {
+            //~^ ERROR: infinite loop detected
+            do_something();
+        }
+    };
+
+    let _somehow_ok = || -> ! {
+        loop {
+            do_something();
+        }
+    };
+}
+
 fn main() {}