1 files changed, 137 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/blocks_in_conditions.rs b/src/tools/clippy/clippy_lints/src/blocks_in_conditions.rs
new file mode 100644
index 000000000..1417e230a
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/blocks_in_conditions.rs
@@ -0,0 +1,137 @@
+use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg};
+use clippy_utils::source::snippet_block_with_applicability;
+use clippy_utils::ty::implements_trait;
+use clippy_utils::visitors::{for_each_expr, Descend};
+use clippy_utils::{get_parent_expr, higher};
+use core::ops::ControlFlow;
+use rustc_errors::Applicability;
+use rustc_hir::{BlockCheckMode, Expr, ExprKind, MatchSource};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_session::declare_lint_pass;
+use rustc_span::sym;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for `if` conditions that use blocks containing an
+    /// expression, statements or conditions that use closures with blocks.
+    ///
+    /// ### Why is this bad?
+    /// Style, using blocks in the condition makes it hard to read.
+    ///
+    /// ### Examples
+    /// ```no_run
+    /// # fn somefunc() -> bool { true };
+    /// if { true } { /* ... */ }
+    ///
+    /// if { let x = somefunc(); x } { /* ... */ }
+    /// ```
+    ///
+    /// Use instead:
+    /// ```no_run
+    /// # fn somefunc() -> bool { true };
+    /// if true { /* ... */ }
+    ///
+    /// let res = { let x = somefunc(); x };
+    /// if res { /* ... */ }
+    /// ```
+    #[clippy::version = "1.45.0"]
+    pub BLOCKS_IN_CONDITIONS,
+    style,
+    "useless or complex blocks that can be eliminated in conditions"
+}
+
+declare_lint_pass!(BlocksInConditions => [BLOCKS_IN_CONDITIONS]);
+
+const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
+
+impl<'tcx> LateLintPass<'tcx> for BlocksInConditions {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+        if in_external_macro(cx.sess(), expr.span) {
+            return;
+        }
+
+        let Some((cond, keyword, desc)) = higher::If::hir(expr)
+            .map(|hif| (hif.cond, "if", "an `if` condition"))
+            .or(if let ExprKind::Match(match_ex, _, MatchSource::Normal) = expr.kind {
+                Some((match_ex, "match", "a `match` scrutinee"))
+            } else {
+                None
+            })
+        else {
+            return;
+        };
+        let complex_block_message = &format!(
+            "in {desc}, avoid complex blocks or closures with blocks; \
+            instead, move the block or closure higher and bind it with a `let`",
+        );
+
+        if let ExprKind::Block(block, _) = &cond.kind {
+            if block.rules == BlockCheckMode::DefaultBlock {
+                if block.stmts.is_empty() {
+                    if let Some(ex) = &block.expr {
+                        // don't dig into the expression here, just suggest that they remove
+                        // the block
+                        if expr.span.from_expansion() || ex.span.from_expansion() {
+                            return;
+                        }
+                        let mut applicability = Applicability::MachineApplicable;
+                        span_lint_and_sugg(
+                            cx,
+                            BLOCKS_IN_CONDITIONS,
+                            cond.span,
+                            BRACED_EXPR_MESSAGE,
+                            "try",
+                            snippet_block_with_applicability(cx, ex.span, "..", Some(expr.span), &mut applicability)
+                                .to_string(),
+                            applicability,
+                        );
+                    }
+                } else {
+                    let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
+                    if span.from_expansion() || expr.span.from_expansion() {
+                        return;
+                    }
+                    // move block higher
+                    let mut applicability = Applicability::MachineApplicable;
+                    span_lint_and_sugg(
+                        cx,
+                        BLOCKS_IN_CONDITIONS,
+                        expr.span.with_hi(cond.span.hi()),
+                        complex_block_message,
+                        "try",
+                        format!(
+                            "let res = {}; {keyword} res",
+                            snippet_block_with_applicability(cx, block.span, "..", Some(expr.span), &mut applicability),
+                        ),
+                        applicability,
+                    );
+                }
+            }
+        } else {
+            let _: Option<!> = for_each_expr(cond, |e| {
+                if let ExprKind::Closure(closure) = e.kind {
+                    // do not lint if the closure is called using an iterator (see #1141)
+                    if let Some(parent) = get_parent_expr(cx, e)
+                        && let ExprKind::MethodCall(_, self_arg, _, _) = &parent.kind
+                        && let caller = cx.typeck_results().expr_ty(self_arg)
+                        && let Some(iter_id) = cx.tcx.get_diagnostic_item(sym::Iterator)
+                        && implements_trait(cx, caller, iter_id, &[])
+                    {
+                        return ControlFlow::Continue(Descend::No);
+                    }
+
+                    let body = cx.tcx.hir().body(closure.body);
+                    let ex = &body.value;
+                    if let ExprKind::Block(block, _) = ex.kind {
+                        if !body.value.span.from_expansion() && !block.stmts.is_empty() {
+                            span_lint(cx, BLOCKS_IN_CONDITIONS, ex.span, complex_block_message);
+                            return ControlFlow::Continue(Descend::No);
+                        }
+                    }
+                }
+                ControlFlow::Continue(Descend::Yes)
+            });
+        }
+    }
+}