[needless_continue]: lint if the last stmt in for/while/loop is continue, recursively

Fixes: #4077

Author: lengyijun

Diff for: clippy_lints/src/methods/unnecessary_to_owned.rs

@@ -379,7 +379,7 @@ fn can_change_type<'a>(cx: &LateContext<'a>, mut expr: &'a Expr<'a>, mut ty: Ty<
     for (_, node) in cx.tcx.hir().parent_iter(expr.hir_id) {
         match node {
             Node::Stmt(_) => return true,
-            Node::Block(..) => continue,
+            Node::Block(..) => {}
             Node::Item(item) => {
                 if let ItemKind::Fn(_, _, body_id) = &item.kind
                 && let output_ty = return_ty(cx, item.owner_id)

Diff for: clippy_lints/src/needless_continue.rs

@@ -35,7 +35,7 @@
 //! This lint is **warn** by default.
 use clippy_utils::diagnostics::span_lint_and_help;
 use clippy_utils::source::{indent_of, snippet, snippet_block};
-use rustc_ast::ast;
+use rustc_ast::{ast, Block, Label};
 use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::Span;
@@ -361,24 +361,68 @@ fn suggestion_snippet_for_continue_inside_else(cx: &EarlyContext<'_>, data: &Lin
     )
 }
 
-fn check_and_warn(cx: &EarlyContext<'_>, expr: &ast::Expr) {
-    if_chain! {
-        if let ast::ExprKind::Loop(loop_block, ..) = &expr.kind;
-        if let Some(last_stmt) = loop_block.stmts.last();
-        if let ast::StmtKind::Expr(inner_expr) | ast::StmtKind::Semi(inner_expr) = &last_stmt.kind;
-        if let ast::ExprKind::Continue(_) = inner_expr.kind;
-        then {
-            span_lint_and_help(
-                cx,
-                NEEDLESS_CONTINUE,
-                last_stmt.span,
-                MSG_REDUNDANT_CONTINUE_EXPRESSION,
-                None,
-                DROP_CONTINUE_EXPRESSION_MSG,
-            );
+fn check_last_stmt<F>(b: &Block, func: &F)
+where
+    F: Fn(Option<&ast::Label>, Span),
+{
+    if let Some(last_stmt) = b.stmts.last() &&
+       let ast::StmtKind::Expr(inner_expr) | ast::StmtKind::Semi(inner_expr) = &last_stmt.kind {
+        match &inner_expr.kind {
+            rustc_ast::ExprKind::Continue(continue_label) => {
+                func(continue_label.as_ref(), last_stmt.span);
+            },
+
+            rustc_ast::ExprKind::If(_, then_block, else_block) => {
+                check_last_stmt(then_block, func);
+                if let Some(else_block) = else_block {
+                    match &else_block.kind {
+                        rustc_ast::ExprKind::Continue(continue_label) => {
+                            func(continue_label.as_ref(), else_block.span);
+                        }
+                        rustc_ast::ExprKind::Block(b, _) => {
+                            check_last_stmt(b, func);
+                        }
+                        _ => {}
+
+                    }
+                }
+            }
+            rustc_ast::ExprKind::Match(_, arms) => {
+                for arm in arms {
+                    match &arm.body.kind {
+                        rustc_ast::ExprKind::Continue(continue_label) => {
+                            func(continue_label.as_ref(), arm.body.span);
+                        }
+                        rustc_ast::ExprKind::Block(b, _) => {
+                            check_last_stmt(b, func);
+
+                        }
+                        _ => {}
+                    }
+
+                }
+            }
+            _ => {},
         }
     }
+}
+
+fn check_and_warn(cx: &EarlyContext<'_>, expr: &ast::Expr) {
     with_loop_block(expr, |loop_block, label| {
+        let p = |continue_label: Option<&Label>, span: Span| {
+            if compare_labels(label, continue_label) {
+                span_lint_and_help(
+                    cx,
+                    NEEDLESS_CONTINUE,
+                    span,
+                    MSG_REDUNDANT_CONTINUE_EXPRESSION,
+                    None,
+                    DROP_CONTINUE_EXPRESSION_MSG,
+                );
+            }
+        };
+        check_last_stmt(loop_block, &p);
+
         for (i, stmt) in loop_block.stmts.iter().enumerate() {
             with_if_expr(stmt, |if_expr, cond, then_block, else_expr| {
                 let data = &LintData {

Diff for: clippy_lints/src/redundant_else.rs

@@ -69,7 +69,6 @@ impl EarlyLintPass for RedundantElse {
                 ExprKind::If(_, next_then, Some(next_els)) => {
                     then = next_then;
                     els = next_els;
-                    continue;
                 },
                 // else if without else
                 ExprKind::If(..) => return,

Diff for: clippy_lints/src/transmute/transmute_undefined_repr.rs

@@ -30,19 +30,16 @@ pub(super) fn check<'tcx>(
             | (ReducedTy::UnorderedFields(from_sub_ty), ReducedTy::OrderedFields(_, Some(to_sub_ty))) => {
                 from_ty = from_sub_ty;
                 to_ty = to_sub_ty;
-                continue;
             },
             (ReducedTy::OrderedFields(_, Some(from_sub_ty)), ReducedTy::Other(to_sub_ty)) if reduced_tys.to_fat_ptr => {
                 from_ty = from_sub_ty;
                 to_ty = to_sub_ty;
-                continue;
             },
             (ReducedTy::Other(from_sub_ty), ReducedTy::OrderedFields(_, Some(to_sub_ty)))
                 if reduced_tys.from_fat_ptr =>
             {
                 from_ty = from_sub_ty;
                 to_ty = to_sub_ty;
-                continue;
             },
 
             // ptr <-> ptr
@@ -52,7 +49,6 @@ pub(super) fn check<'tcx>(
             {
                 from_ty = from_sub_ty;
                 to_ty = to_sub_ty;
-                continue;
             },
 
             // fat ptr <-> (*size, *size)

Diff for: tests/missing-test-files.rs

@@ -60,7 +60,7 @@ fn explore_directory(dir: &Path) -> Vec<String> {
                             missing_files.push(path.to_str().unwrap().to_string());
                         }
                     },
-                    _ => continue,
+                    _ => {},
                 };
             }
         }

Diff for: tests/ui/needless_continue.rs

@@ -151,3 +151,25 @@ mod issue_2329 {
         }
     }
 }
+
+mod issue_4077 {
+    fn main() {
+        loop {
+            do_something();
+            if some_expr() {
+                continue;
+            }
+        }
+    }
+
+    // The contents of these functions are irrelevant, the purpose of this file is
+    // shown in main.
+
+    fn do_something() {
+        std::process::exit(0);
+    }
+
+    fn some_expr() -> bool {
+        true
+    }
+}

Diff for: tests/ui/needless_continue.stderr

@@ -136,5 +136,13 @@ LL | |                 }
                                println!("bar-5");
                            }
 
-error: aborting due to 8 previous errors
+error: this `continue` expression is redundant
+  --> $DIR/needless_continue.rs:160:17
+   |
+LL |                 continue;
+   |                 ^^^^^^^^^
+   |
+   = help: consider dropping the `continue` expression
+
+error: aborting due to 9 previous errors