1 files changed, 155 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/blocks_in_if_conditions.rs b/src/tools/clippy/clippy_lints/src/blocks_in_if_conditions.rs
new file mode 100644
index 000000000..ad206b5fb
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/blocks_in_if_conditions.rs
@@ -0,0 +1,155 @@
+use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg};
+use clippy_utils::get_parent_expr;
+use clippy_utils::higher;
+use clippy_utils::source::snippet_block_with_applicability;
+use clippy_utils::ty::implements_trait;
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir::intravisit::{walk_expr, Visitor};
+use rustc_hir::{BlockCheckMode, Closure, Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+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
+    /// ```rust
+    /// # fn somefunc() -> bool { true };
+    /// if { true } { /* ... */ }
+    ///
+    /// if { let x = somefunc(); x } { /* ... */ }
+    /// ```
+    ///
+    /// Use instead:
+    /// ```rust
+    /// # fn somefunc() -> bool { true };
+    /// if true { /* ... */ }
+    ///
+    /// let res = { let x = somefunc(); x };
+    /// if res { /* ... */ }
+    /// ```
+    #[clippy::version = "1.45.0"]
+    pub BLOCKS_IN_IF_CONDITIONS,
+    style,
+    "useless or complex blocks that can be eliminated in conditions"
+}
+
+declare_lint_pass!(BlocksInIfConditions => [BLOCKS_IN_IF_CONDITIONS]);
+
+struct ExVisitor<'a, 'tcx> {
+    found_block: Option<&'tcx Expr<'tcx>>,
+    cx: &'a LateContext<'tcx>,
+}
+
+impl<'a, 'tcx> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
+    fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
+        if let ExprKind::Closure(&Closure { body, .. }) = expr.kind {
+            // do not lint if the closure is called using an iterator (see #1141)
+            if_chain! {
+                if let Some(parent) = get_parent_expr(self.cx, expr);
+                if let ExprKind::MethodCall(_, [self_arg, ..], _) = &parent.kind;
+                let caller = self.cx.typeck_results().expr_ty(self_arg);
+                if let Some(iter_id) = self.cx.tcx.get_diagnostic_item(sym::Iterator);
+                if implements_trait(self.cx, caller, iter_id, &[]);
+                then {
+                    return;
+                }
+            }
+
+            let body = self.cx.tcx.hir().body(body);
+            let ex = &body.value;
+            if let ExprKind::Block(block, _) = ex.kind {
+                if !body.value.span.from_expansion() && !block.stmts.is_empty() {
+                    self.found_block = Some(ex);
+                    return;
+                }
+            }
+        }
+        walk_expr(self, expr);
+    }
+}
+
+const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
+const COMPLEX_BLOCK_MESSAGE: &str = "in an `if` condition, avoid complex blocks or closures with blocks; \
+                                    instead, move the block or closure higher and bind it with a `let`";
+
+impl<'tcx> LateLintPass<'tcx> for BlocksInIfConditions {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+        if in_external_macro(cx.sess(), expr.span) {
+            return;
+        }
+        if let Some(higher::If { cond, .. }) = higher::If::hir(expr) {
+            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_IF_CONDITIONS,
+                                cond.span,
+                                BRACED_EXPR_MESSAGE,
+                                "try",
+                                format!(
+                                    "{}",
+                                    snippet_block_with_applicability(
+                                        cx,
+                                        ex.span,
+                                        "..",
+                                        Some(expr.span),
+                                        &mut applicability
+                                    )
+                                ),
+                                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_IF_CONDITIONS,
+                            expr.span.with_hi(cond.span.hi()),
+                            COMPLEX_BLOCK_MESSAGE,
+                            "try",
+                            format!(
+                                "let res = {}; if res",
+                                snippet_block_with_applicability(
+                                    cx,
+                                    block.span,
+                                    "..",
+                                    Some(expr.span),
+                                    &mut applicability
+                                ),
+                            ),
+                            applicability,
+                        );
+                    }
+                }
+            } else {
+                let mut visitor = ExVisitor { found_block: None, cx };
+                walk_expr(&mut visitor, cond);
+                if let Some(block) = visitor.found_block {
+                    span_lint(cx, BLOCKS_IN_IF_CONDITIONS, block.span, COMPLEX_BLOCK_MESSAGE);
+                }
+            }
+        }
+    }
+}