Auto merge of rust-lang#10924 - est31:manual_let_else_question_mark, r=Centri3,flip1995,Manishearth

Don't lint manual_let_else in cases where ? would work

Don't lint `manual_let_else` where the question mark operator `?` would be sufficient, that is, mostly in cases like:

```Rust
let v = if let Some(v) = ex { v } else { return None };
```

Also, this PR emits the `question_mark` lint for `let...else` patterns that could be written with `?` (also, only `return None` like cases).

```
changelog: [`manual_let_else`]: don't lint in cases where question_mark already lints
changelog: [`question_mark`]: lint for `let Some(...) = ex else { return None };`
```

Fixes  rust-lang#8755

Author: bors

clippy_lints/src/lib.rs

@@ -663,7 +663,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     });
     store.register_late_pass(move |_| Box::new(matches::Matches::new(msrv())));
     let matches_for_let_else = conf.matches_for_let_else;
-    store.register_late_pass(move |_| Box::new(manual_let_else::ManualLetElse::new(msrv(), matches_for_let_else)));
     store.register_early_pass(move || Box::new(manual_non_exhaustive::ManualNonExhaustiveStruct::new(msrv())));
     store.register_late_pass(move |_| Box::new(manual_non_exhaustive::ManualNonExhaustiveEnum::new(msrv())));
     store.register_late_pass(move |_| Box::new(manual_strip::ManualStrip::new(msrv())));
@@ -772,7 +771,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|_| Box::<useless_conversion::UselessConversion>::default());
     store.register_late_pass(|_| Box::new(implicit_hasher::ImplicitHasher));
     store.register_late_pass(|_| Box::new(fallible_impl_from::FallibleImplFrom));
-    store.register_late_pass(|_| Box::<question_mark::QuestionMark>::default());
+    store.register_late_pass(move |_| Box::new(question_mark::QuestionMark::new(msrv(), matches_for_let_else)));
     store.register_late_pass(|_| Box::new(question_mark_used::QuestionMarkUsed));
     store.register_early_pass(|| Box::new(suspicious_operation_groupings::SuspiciousOperationGroupings));
     store.register_late_pass(|_| Box::new(suspicious_trait_impl::SuspiciousImpl));

clippy_lints/src/manual_let_else.rs

@@ -1,18 +1,17 @@
+use crate::question_mark::{QuestionMark, QUESTION_MARK};
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::higher::IfLetOrMatch;
-use clippy_utils::msrvs::{self, Msrv};
-use clippy_utils::peel_blocks;
 use clippy_utils::source::snippet_with_context;
 use clippy_utils::ty::is_type_diagnostic_item;
 use clippy_utils::visitors::{Descend, Visitable};
-use if_chain::if_chain;
+use clippy_utils::{is_lint_allowed, msrvs, pat_and_expr_can_be_question_mark, peel_blocks};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::{walk_expr, Visitor};
 use rustc_hir::{Expr, ExprKind, HirId, ItemId, Local, MatchSource, Pat, PatKind, QPath, Stmt, StmtKind, Ty};
-use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_lint::{LateContext, LintContext};
 use rustc_middle::lint::in_external_macro;
-use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_session::declare_tool_lint;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::Span;
 use serde::Deserialize;
@@ -50,25 +49,8 @@ declare_clippy_lint! {
     "manual implementation of a let...else statement"
 }
 
-pub struct ManualLetElse {
-    msrv: Msrv,
-    matches_behaviour: MatchLintBehaviour,
-}
-
-impl ManualLetElse {
-    #[must_use]
-    pub fn new(msrv: Msrv, matches_behaviour: MatchLintBehaviour) -> Self {
-        Self {
-            msrv,
-            matches_behaviour,
-        }
-    }
-}
-
-impl_lint_pass!(ManualLetElse => [MANUAL_LET_ELSE]);
-
-impl<'tcx> LateLintPass<'tcx> for ManualLetElse {
-    fn check_stmt(&mut self, cx: &LateContext<'_>, stmt: &'tcx Stmt<'tcx>) {
+impl<'tcx> QuestionMark {
+    pub(crate) fn check_manual_let_else(&mut self, cx: &LateContext<'_>, stmt: &'tcx Stmt<'tcx>) {
         if !self.msrv.meets(msrvs::LET_ELSE) || in_external_macro(cx.sess(), stmt.span) {
             return;
         }
@@ -81,11 +63,14 @@ impl<'tcx> LateLintPass<'tcx> for ManualLetElse {
             let Some(if_let_or_match) = IfLetOrMatch::parse(cx, init)
         {
             match if_let_or_match {
-                IfLetOrMatch::IfLet(if_let_expr, let_pat, if_then, if_else) => if_chain! {
-                    if let Some(ident_map) = expr_simple_identity_map(local.pat, let_pat, if_then);
-                    if let Some(if_else) = if_else;
-                    if expr_diverges(cx, if_else);
-                    then {
+                IfLetOrMatch::IfLet(if_let_expr, let_pat, if_then, if_else) => {
+                    if
+                        let Some(ident_map) = expr_simple_identity_map(local.pat, let_pat, if_then) &&
+                        let Some(if_else) = if_else &&
+                        expr_diverges(cx, if_else) &&
+                        let qm_allowed = is_lint_allowed(cx, QUESTION_MARK, stmt.hir_id) &&
+                        (qm_allowed || pat_and_expr_can_be_question_mark(cx, let_pat, if_else).is_none())
+                    {
                         emit_manual_let_else(cx, stmt.span, if_let_expr, &ident_map, let_pat, if_else);
                     }
                 },
@@ -128,8 +113,6 @@ impl<'tcx> LateLintPass<'tcx> for ManualLetElse {
             }
         };
     }
-
-    extract_msrv_attr!(LateContext);
 }
 
 fn emit_manual_let_else(

clippy_lints/src/manual_rem_euclid.rs

@@ -119,7 +119,7 @@ fn check_for_either_unsigned_int_constant<'a>(
 }
 
 fn check_for_unsigned_int_constant<'a>(cx: &'a LateContext<'_>, expr: &'a Expr<'_>) -> Option<u128> {
-    let Some(int_const) = constant_full_int(cx, cx.typeck_results(), expr) else { return None };
+    let int_const = constant_full_int(cx, cx.typeck_results(), expr)?;
     match int_const {
         FullInt::S(s) => s.try_into().ok(),
         FullInt::U(u) => Some(u),

clippy_lints/src/question_mark.rs

@@ -1,16 +1,20 @@
+use crate::manual_let_else::{MatchLintBehaviour, MANUAL_LET_ELSE};
 use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::msrvs::Msrv;
 use clippy_utils::source::snippet_with_applicability;
 use clippy_utils::ty::is_type_diagnostic_item;
 use clippy_utils::{
-    eq_expr_value, get_parent_node, in_constant, is_else_clause, is_res_lang_ctor, path_to_local, path_to_local_id,
-    peel_blocks, peel_blocks_with_stmt,
+    eq_expr_value, get_parent_node, in_constant, is_else_clause, is_res_lang_ctor, pat_and_expr_can_be_question_mark,
+    path_to_local, path_to_local_id, peel_blocks, peel_blocks_with_stmt,
 };
 use clippy_utils::{higher, is_path_lang_item};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::def::Res;
 use rustc_hir::LangItem::{self, OptionNone, OptionSome, ResultErr, ResultOk};
-use rustc_hir::{BindingAnnotation, ByRef, Expr, ExprKind, Node, PatKind, PathSegment, QPath};
+use rustc_hir::{
+    BindingAnnotation, Block, ByRef, Expr, ExprKind, Local, Node, PatKind, PathSegment, QPath, Stmt, StmtKind,
+};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::Ty;
 use rustc_session::declare_tool_lint;
@@ -42,16 +46,29 @@ declare_clippy_lint! {
     "checks for expressions that could be replaced by the question mark operator"
 }
 
-#[derive(Default)]
 pub struct QuestionMark {
+    pub(crate) msrv: Msrv,
+    pub(crate) matches_behaviour: MatchLintBehaviour,
     /// Keeps track of how many try blocks we are in at any point during linting.
     /// This allows us to answer the question "are we inside of a try block"
     /// very quickly, without having to walk up the parent chain, by simply checking
     /// if it is greater than zero.
     /// As for why we need this in the first place: <https://github.com/rust-lang/rust-clippy/issues/8628>
     try_block_depth_stack: Vec<u32>,
 }
-impl_lint_pass!(QuestionMark => [QUESTION_MARK]);
+
+impl_lint_pass!(QuestionMark => [QUESTION_MARK, MANUAL_LET_ELSE]);
+
+impl QuestionMark {
+    #[must_use]
+    pub fn new(msrv: Msrv, matches_behaviour: MatchLintBehaviour) -> Self {
+        Self {
+            msrv,
+            matches_behaviour,
+            try_block_depth_stack: Vec::new(),
+        }
+    }
+}
 
 enum IfBlockType<'hir> {
     /// An `if x.is_xxx() { a } else { b } ` expression.
@@ -78,6 +95,29 @@ enum IfBlockType<'hir> {
     ),
 }
 
+fn check_let_some_else_return_none(cx: &LateContext<'_>, stmt: &Stmt<'_>) {
+    if let StmtKind::Local(Local { pat, init: Some(init_expr), els: Some(els), .. }) = stmt.kind &&
+        let Block { stmts: &[], expr: Some(els), .. } = els &&
+        let Some(inner_pat) = pat_and_expr_can_be_question_mark(cx, pat, els)
+    {
+        let mut applicability = Applicability::MaybeIncorrect;
+        let init_expr_str = snippet_with_applicability(cx, init_expr.span, "..", &mut applicability);
+        let receiver_str = snippet_with_applicability(cx, inner_pat.span, "..", &mut applicability);
+        let sugg = format!(
+            "let {receiver_str} = {init_expr_str}?;",
+        );
+        span_lint_and_sugg(
+            cx,
+            QUESTION_MARK,
+            stmt.span,
+            "this `let...else` may be rewritten with the `?` operator",
+            "replace it with",
+            sugg,
+            applicability,
+        );
+    }
+}
+
 fn is_early_return(smbl: Symbol, cx: &LateContext<'_>, if_block: &IfBlockType<'_>) -> bool {
     match *if_block {
         IfBlockType::IfIs(caller, caller_ty, call_sym, if_then, _) => {
@@ -259,6 +299,12 @@ fn is_try_block(cx: &LateContext<'_>, bl: &rustc_hir::Block<'_>) -> bool {
 }
 
 impl<'tcx> LateLintPass<'tcx> for QuestionMark {
+    fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
+        if !in_constant(cx, stmt.hir_id) {
+            check_let_some_else_return_none(cx, stmt);
+        }
+        self.check_manual_let_else(cx, stmt);
+    }
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if !in_constant(cx, expr.hir_id) {
             self.check_is_none_or_err_and_early_return(cx, expr);
@@ -291,4 +337,5 @@ impl<'tcx> LateLintPass<'tcx> for QuestionMark {
                 .expect("blocks are always part of bodies and must have a depth") -= 1;
         }
     }
+    extract_msrv_attr!(LateContext);
 }

clippy_utils/src/lib.rs

@@ -87,6 +87,7 @@ use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, LOCAL_CRATE};
 use rustc_hir::hir_id::{HirIdMap, HirIdSet};
 use rustc_hir::intravisit::{walk_expr, FnKind, Visitor};
+use rustc_hir::LangItem::OptionSome;
 use rustc_hir::LangItem::{OptionNone, ResultErr, ResultOk};
 use rustc_hir::{
     self as hir, def, Arm, ArrayLen, BindingAnnotation, Block, BlockCheckMode, Body, Closure, Destination, Expr,
@@ -2543,6 +2544,50 @@ pub fn span_find_starting_semi(sm: &SourceMap, span: Span) -> Span {
     sm.span_take_while(span, |&ch| ch == ' ' || ch == ';')
 }
 
+/// Returns whether the given let pattern and else body can be turned into a question mark
+///
+/// For this example:
+/// ```ignore
+/// let FooBar { a, b } = if let Some(a) = ex { a } else { return None };
+/// ```
+/// We get as parameters:
+/// ```ignore
+/// pat: Some(a)
+/// else_body: return None
+/// ```
+
+/// And for this example:
+/// ```ignore
+/// let Some(FooBar { a, b }) = ex else { return None };
+/// ```
+/// We get as parameters:
+/// ```ignore
+/// pat: Some(FooBar { a, b })
+/// else_body: return None
+/// ```
+
+/// We output `Some(a)` in the first instance, and `Some(FooBar { a, b })` in the second, because
+/// the question mark operator is applicable here. Callers have to check whether we are in a
+/// constant or not.
+pub fn pat_and_expr_can_be_question_mark<'a, 'hir>(
+    cx: &LateContext<'_>,
+    pat: &'a Pat<'hir>,
+    else_body: &Expr<'_>,
+) -> Option<&'a Pat<'hir>> {
+    if let PatKind::TupleStruct(pat_path, [inner_pat], _) = pat.kind &&
+        is_res_lang_ctor(cx, cx.qpath_res(&pat_path, pat.hir_id), OptionSome) &&
+        !is_refutable(cx, inner_pat) &&
+        let else_body = peel_blocks(else_body) &&
+        let ExprKind::Ret(Some(ret_val)) = else_body.kind &&
+        let ExprKind::Path(ret_path) = ret_val.kind &&
+        is_res_lang_ctor(cx, cx.qpath_res(&ret_path, ret_val.hir_id), OptionNone)
+    {
+        Some(inner_pat)
+    } else {
+        None
+    }
+}
+
 macro_rules! op_utils {
     ($($name:ident $assign:ident)*) => {
         /// Binary operation traits like `LangItem::Add`

tests/ui/manual_let_else_question_mark.fixed

@@ -0,0 +1,63 @@
+//@run-rustfix
+#![allow(unused_braces, unused_variables, dead_code)]
+#![allow(
+    clippy::collapsible_else_if,
+    clippy::unused_unit,
+    clippy::let_unit_value,
+    clippy::match_single_binding,
+    clippy::never_loop
+)]
+#![warn(clippy::manual_let_else, clippy::question_mark)]
+
+enum Variant {
+    A(usize, usize),
+    B(usize),
+    C,
+}
+
+fn g() -> Option<(u8, u8)> {
+    None
+}
+
+fn e() -> Variant {
+    Variant::A(0, 0)
+}
+
+fn main() {}
+
+fn foo() -> Option<()> {
+    // Fire here, normal case
+    let v = g()?;
+
+    // Don't fire here, the pattern is refutable
+    let Variant::A(v, w) = e() else { return None };
+
+    // Fire here, the pattern is irrefutable
+    let (v, w) = g()?;
+
+    // Don't fire manual_let_else in this instance: question mark can be used instead.
+    let v = g()?;
+
+    // Do fire manual_let_else in this instance: question mark cannot be used here due to the return
+    // body.
+    let Some(v) = g() else {
+        return Some(());
+    };
+
+    // Here we could also fire the question_mark lint, but we don't (as it's a match and not an if let).
+    // So we still emit manual_let_else here. For the *resulting* code, we *do* emit the question_mark
+    // lint, so for rustfix reasons, we allow the question_mark lint here.
+    #[allow(clippy::question_mark)]
+    {
+        let Some(v) = g() else { return None };
+    }
+
+    // This is a copy of the case above where we'd fire the question_mark lint, but here we have allowed
+    // it. Make sure that manual_let_else is fired as the fallback.
+    #[allow(clippy::question_mark)]
+    {
+        let Some(v) = g() else { return None };
+    }
+
+    Some(())
+}