Auto merge of #11974 - y21:if_let_true, r=llogiq

[`redundant_pattern_matching`]: lint `if let true`, `while let true`, `matches!(.., true)`

Closes #11917

This could also lint e.g. `if let (true, true, false) = (a, b, c)` and suggest `if a && b && c`, but that's a change in semantics (going from eager to lazy, so I just left it out for now. Could be a future improvement.

changelog: [`redundant_pattern_matching`]: lint `if let true`, `while let true`, `matches!(.., true)`

Author: bors

clippy_lints/src/format_push_string.rs

@@ -57,7 +57,7 @@ fn is_format(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
             Some(higher::IfLetOrMatch::Match(_, arms, MatchSource::Normal)) => {
                 arms.iter().any(|arm| is_format(cx, arm.body))
             },
-            Some(higher::IfLetOrMatch::IfLet(_, _, then, r#else)) => {
+            Some(higher::IfLetOrMatch::IfLet(_, _, then, r#else, _)) => {
                 is_format(cx, then) || r#else.is_some_and(|e| is_format(cx, e))
             },
             _ => false,

clippy_lints/src/loops/manual_flatten.rs

@@ -20,7 +20,7 @@ pub(super) fn check<'tcx>(
     span: Span,
 ) {
     let inner_expr = peel_blocks_with_stmt(body);
-    if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: None })
+    if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: None, .. })
             = higher::IfLet::hir(cx, inner_expr)
         // Ensure match_expr in `if let` statement is the same as the pat from the for-loop
         && let PatKind::Binding(_, pat_hir_id, _, _) = pat.kind

clippy_lints/src/loops/while_let_on_iterator.rs

@@ -14,7 +14,7 @@ use rustc_span::symbol::sym;
 use rustc_span::Symbol;
 
 pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-    if let Some(higher::WhileLet { if_then, let_pat, let_expr }) = higher::WhileLet::hir(expr)
+    if let Some(higher::WhileLet { if_then, let_pat, let_expr, .. }) = higher::WhileLet::hir(expr)
         // check for `Some(..)` pattern
         && let PatKind::TupleStruct(ref pat_path, some_pat, _) = let_pat.kind
         && is_res_lang_ctor(cx, cx.qpath_res(pat_path, let_pat.hir_id), LangItem::OptionSome)

clippy_lints/src/manual_let_else.rs

@@ -61,7 +61,7 @@ impl<'tcx> QuestionMark {
             && 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) => {
+                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
                         && is_never_expr(cx, if_else).is_some()

clippy_lints/src/matches/collapsible_match.rs

@@ -41,7 +41,7 @@ fn check_arm<'tcx>(
     let inner_expr = peel_blocks_with_stmt(outer_then_body);
     if let Some(inner) = IfLetOrMatch::parse(cx, inner_expr)
         && let Some((inner_scrutinee, inner_then_pat, inner_else_body)) = match inner {
-            IfLetOrMatch::IfLet(scrutinee, pat, _, els) => Some((scrutinee, pat, els)),
+            IfLetOrMatch::IfLet(scrutinee, pat, _, els, _) => Some((scrutinee, pat, els)),
             IfLetOrMatch::Match(scrutinee, arms, ..) => if arms.len() == 2 && arms.iter().all(|a| a.guard.is_none())
                 // if there are more than two arms, collapsing would be non-trivial
                 // one of the arms must be "wild-like"
@@ -75,7 +75,7 @@ fn check_arm<'tcx>(
         )
         // ...or anywhere in the inner expression
         && match inner {
-            IfLetOrMatch::IfLet(_, _, body, els) => {
+            IfLetOrMatch::IfLet(_, _, body, els, _) => {
                 !is_local_used(cx, body, binding_id) && els.map_or(true, |e| !is_local_used(cx, e, binding_id))
             },
             IfLetOrMatch::Match(_, arms, ..) => !arms.iter().any(|arm| is_local_used(cx, arm, binding_id)),

clippy_lints/src/matches/mod.rs

@@ -469,15 +469,15 @@ declare_clippy_lint! {
 declare_clippy_lint! {
     /// ### What it does
     /// Lint for redundant pattern matching over `Result`, `Option`,
-    /// `std::task::Poll` or `std::net::IpAddr`
+    /// `std::task::Poll`, `std::net::IpAddr` or `bool`s
     ///
     /// ### Why is this bad?
     /// It's more concise and clear to just use the proper
-    /// utility function
+    /// utility function or using the condition directly
     ///
     /// ### Known problems
-    /// This will change the drop order for the matched type. Both `if let` and
-    /// `while let` will drop the value at the end of the block, both `if` and `while` will drop the
+    /// For suggestions involving bindings in patterns, this will change the drop order for the matched type.
+    /// Both `if let` and `while let` will drop the value at the end of the block, both `if` and `while` will drop the
     /// value before entering the block. For most types this change will not matter, but for a few
     /// types this will not be an acceptable change (e.g. locks). See the
     /// [reference](https://doc.rust-lang.org/reference/destructors.html#drop-scopes) for more about
@@ -499,6 +499,10 @@ declare_clippy_lint! {
     ///     Ok(_) => true,
     ///     Err(_) => false,
     /// };
+    ///
+    /// let cond = true;
+    /// if let true = cond {}
+    /// matches!(cond, true);
     /// ```
     ///
     /// The more idiomatic use would be:
@@ -515,6 +519,10 @@ declare_clippy_lint! {
     /// if IpAddr::V4(Ipv4Addr::LOCALHOST).is_ipv4() {}
     /// if IpAddr::V6(Ipv6Addr::LOCALHOST).is_ipv6() {}
     /// Ok::<i32, i32>(42).is_ok();
+    ///
+    /// let cond = true;
+    /// if cond {}
+    /// cond;
     /// ```
     #[clippy::version = "1.31.0"]
     pub REDUNDANT_PATTERN_MATCHING,
@@ -1019,8 +1027,11 @@ impl<'tcx> LateLintPass<'tcx> for Matches {
         let from_expansion = expr.span.from_expansion();
 
         if let ExprKind::Match(ex, arms, source) = expr.kind {
-            if is_direct_expn_of(expr.span, "matches").is_some() {
+            if is_direct_expn_of(expr.span, "matches").is_some()
+                && let [arm, _] = arms
+            {
                 redundant_pattern_match::check_match(cx, expr, ex, arms);
+                redundant_pattern_match::check_matches_true(cx, expr, arm, ex);
             }
 
             if source == MatchSource::Normal && !is_span_match(cx, expr.span) {
@@ -1104,6 +1115,7 @@ impl<'tcx> LateLintPass<'tcx> for Matches {
                     if_let.let_pat,
                     if_let.let_expr,
                     if_let.if_else.is_some(),
+                    if_let.let_span,
                 );
                 needless_match::check_if_let(cx, expr, &if_let);
             }

clippy_lints/src/matches/redundant_pattern_match.rs

@@ -1,7 +1,7 @@
 use super::REDUNDANT_PATTERN_MATCHING;
 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
 use clippy_utils::source::{snippet, walk_span_to_context};
-use clippy_utils::sugg::Sugg;
+use clippy_utils::sugg::{make_unop, Sugg};
 use clippy_utils::ty::{is_type_diagnostic_item, needs_ordered_drop};
 use clippy_utils::visitors::{any_temporaries_need_ordered_drop, for_each_expr};
 use clippy_utils::{higher, is_expn_of, is_trait_method};
@@ -12,13 +12,20 @@ use rustc_hir::LangItem::{self, OptionNone, OptionSome, PollPending, PollReady,
 use rustc_hir::{Arm, Expr, ExprKind, Guard, Node, Pat, PatKind, QPath, UnOp};
 use rustc_lint::LateContext;
 use rustc_middle::ty::{self, GenericArgKind, Ty};
-use rustc_span::{sym, Symbol};
+use rustc_span::{sym, Span, Symbol};
 use std::fmt::Write;
 use std::ops::ControlFlow;
 
 pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-    if let Some(higher::WhileLet { let_pat, let_expr, .. }) = higher::WhileLet::hir(expr) {
-        find_sugg_for_if_let(cx, expr, let_pat, let_expr, "while", false);
+    if let Some(higher::WhileLet {
+        let_pat,
+        let_expr,
+        let_span,
+        ..
+    }) = higher::WhileLet::hir(expr)
+    {
+        find_method_sugg_for_if_let(cx, expr, let_pat, let_expr, "while", false);
+        find_if_let_true(cx, let_pat, let_expr, let_span);
     }
 }
 
@@ -28,8 +35,73 @@ pub(super) fn check_if_let<'tcx>(
     pat: &'tcx Pat<'_>,
     scrutinee: &'tcx Expr<'_>,
     has_else: bool,
+    let_span: Span,
 ) {
-    find_sugg_for_if_let(cx, expr, pat, scrutinee, "if", has_else);
+    find_if_let_true(cx, pat, scrutinee, let_span);
+    find_method_sugg_for_if_let(cx, expr, pat, scrutinee, "if", has_else);
+}
+
+/// Looks for:
+/// * `matches!(expr, true)`
+pub fn check_matches_true<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'_>,
+    arm: &'tcx Arm<'_>,
+    scrutinee: &'tcx Expr<'_>,
+) {
+    find_match_true(
+        cx,
+        arm.pat,
+        scrutinee,
+        expr.span.source_callsite(),
+        "using `matches!` to pattern match a bool",
+    );
+}
+
+/// Looks for any of:
+/// * `if let true = ...`
+/// * `if let false = ...`
+/// * `while let true = ...`
+fn find_if_let_true<'tcx>(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, scrutinee: &'tcx Expr<'_>, let_span: Span) {
+    find_match_true(cx, pat, scrutinee, let_span, "using `if let` to pattern match a bool");
+}
+
+/// Common logic between `find_if_let_true` and `check_matches_true`
+fn find_match_true<'tcx>(
+    cx: &LateContext<'tcx>,
+    pat: &'tcx Pat<'_>,
+    scrutinee: &'tcx Expr<'_>,
+    span: Span,
+    message: &str,
+) {
+    if let PatKind::Lit(lit) = pat.kind
+        && let ExprKind::Lit(lit) = lit.kind
+        && let LitKind::Bool(pat_is_true) = lit.node
+    {
+        let mut applicability = Applicability::MachineApplicable;
+
+        let mut sugg = Sugg::hir_with_context(
+            cx,
+            scrutinee,
+            scrutinee.span.source_callsite().ctxt(),
+            "..",
+            &mut applicability,
+        );
+
+        if !pat_is_true {
+            sugg = make_unop("!", sugg);
+        }
+
+        span_lint_and_sugg(
+            cx,
+            REDUNDANT_PATTERN_MATCHING,
+            span,
+            message,
+            "consider using the condition directly",
+            sugg.to_string(),
+            applicability,
+        );
+    }
 }
 
 // Extract the generic arguments out of a type
@@ -100,7 +172,7 @@ fn find_method_and_type<'tcx>(
     }
 }
 
-fn find_sugg_for_if_let<'tcx>(
+fn find_method_sugg_for_if_let<'tcx>(
     cx: &LateContext<'tcx>,
     expr: &'tcx Expr<'_>,
     let_pat: &Pat<'_>,

clippy_lints/src/methods/filter_map.rs

@@ -186,7 +186,7 @@ impl<'tcx> OffendingFilterExpr<'tcx> {
                     match higher::IfLetOrMatch::parse(cx, map_body.value) {
                         // For `if let` we want to check that the variant matching arm references the local created by
                         // its pattern
-                        Some(higher::IfLetOrMatch::IfLet(sc, pat, then, Some(else_)))
+                        Some(higher::IfLetOrMatch::IfLet(sc, pat, then, Some(else_), ..))
                             if let Some((ident, span)) = expr_uses_local(pat, then) =>
                         {
                             (sc, else_, ident, span)

clippy_lints/src/option_if_let_else.rs

@@ -238,6 +238,7 @@ fn detect_option_if_let_else<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) ->
         let_expr,
         if_then,
         if_else: Some(if_else),
+        ..
     }) = higher::IfLet::hir(cx, expr)
         && !cx.typeck_results().expr_ty(expr).is_unit()
         && !is_else_clause(cx.tcx, expr)

clippy_lints/src/question_mark.rs

@@ -256,6 +256,7 @@ impl QuestionMark {
                 let_expr,
                 if_then,
                 if_else,
+                ..
             }) = higher::IfLet::hir(cx, expr)
             && !is_else_clause(cx.tcx, expr)
             && let PatKind::TupleStruct(ref path1, [field], ddpos) = let_pat.kind