use crate::utils::{higher, qpath_res, snippet, span_lint_and_then}; use if_chain::if_chain; use rustc::declare_lint_pass; use rustc::hir; use rustc::hir::def::Res; use rustc::hir::BindingAnnotation; use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; use rustc_errors::Applicability; use rustc_session::declare_tool_lint; declare_clippy_lint! { /// **What it does:** Checks for variable declarations immediately followed by a /// conditional affectation. /// /// **Why is this bad?** This is not idiomatic Rust. /// /// **Known problems:** None. /// /// **Example:** /// ```rust,ignore /// let foo; /// /// if bar() { /// foo = 42; /// } else { /// foo = 0; /// } /// /// let mut baz = None; /// /// if bar() { /// baz = Some(42); /// } /// ``` /// /// should be written /// /// ```rust,ignore /// let foo = if bar() { /// 42 /// } else { /// 0 /// }; /// /// let baz = if bar() { /// Some(42) /// } else { /// None /// }; /// ``` pub USELESS_LET_IF_SEQ, style, "unidiomatic `let mut` declaration followed by initialization in `if`" } declare_lint_pass!(LetIfSeq => [USELESS_LET_IF_SEQ]); impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LetIfSeq { fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx hir::Block) { let mut it = block.stmts.iter().peekable(); while let Some(stmt) = it.next() { if_chain! { if let Some(expr) = it.peek(); if let hir::StmtKind::Local(ref local) = stmt.kind; if let hir::PatKind::Binding(mode, canonical_id, ident, None) = local.pat.kind; if let hir::StmtKind::Expr(ref if_) = expr.kind; if let Some((ref cond, ref then, ref else_)) = higher::if_block(&if_); if !used_in_expr(cx, canonical_id, cond); if let hir::ExprKind::Block(ref then, _) = then.kind; if let Some(value) = check_assign(cx, canonical_id, &*then); if !used_in_expr(cx, canonical_id, value); then { let span = stmt.span.to(if_.span); let has_interior_mutability = !cx.tables.node_type(canonical_id).is_freeze( cx.tcx, cx.param_env, span ); if has_interior_mutability { return; } let (default_multi_stmts, default) = if let Some(ref else_) = *else_ { if let hir::ExprKind::Block(ref else_, _) = else_.kind { if let Some(default) = check_assign(cx, canonical_id, else_) { (else_.stmts.len() > 1, default) } else if let Some(ref default) = local.init { (true, &**default) } else { continue; } } else { continue; } } else if let Some(ref default) = local.init { (false, &**default) } else { continue; }; let mutability = match mode { BindingAnnotation::RefMut | BindingAnnotation::Mutable => " ", _ => "", }; // FIXME: this should not suggest `mut` if we can detect that the variable is not // use mutably after the `if` let sug = format!( "let {mut}{name} = if {cond} {{{then} {value} }} else {{{else} {default} }};", mut=mutability, name=ident.name, cond=snippet(cx, cond.span, "_"), then=if then.stmts.len() > 1 { " ..;" } else { "" }, else=if default_multi_stmts { " ..;" } else { "" }, value=snippet(cx, value.span, ""), default=snippet(cx, default.span, ""), ); span_lint_and_then(cx, USELESS_LET_IF_SEQ, span, "`if _ { .. } else { .. }` is an expression", |db| { db.span_suggestion( span, "it is more idiomatic to write", sug, Applicability::HasPlaceholders, ); if !mutability.is_empty() { db.note("you might not need `mut` at all"); } }); } } } } } struct UsedVisitor<'a, 'tcx> { cx: &'a LateContext<'a, 'tcx>, id: hir::HirId, used: bool, } impl<'a, 'tcx> hir::intravisit::Visitor<'tcx> for UsedVisitor<'a, 'tcx> { fn visit_expr(&mut self, expr: &'tcx hir::Expr) { if_chain! { if let hir::ExprKind::Path(ref qpath) = expr.kind; if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id); if self.id == local_id; then { self.used = true; return; } } hir::intravisit::walk_expr(self, expr); } fn nested_visit_map<'this>(&'this mut self) -> hir::intravisit::NestedVisitorMap<'this, 'tcx> { hir::intravisit::NestedVisitorMap::None } } fn check_assign<'a, 'tcx>( cx: &LateContext<'a, 'tcx>, decl: hir::HirId, block: &'tcx hir::Block, ) -> Option<&'tcx hir::Expr> { if_chain! { if block.expr.is_none(); if let Some(expr) = block.stmts.iter().last(); if let hir::StmtKind::Semi(ref expr) = expr.kind; if let hir::ExprKind::Assign(ref var, ref value) = expr.kind; if let hir::ExprKind::Path(ref qpath) = var.kind; if let Res::Local(local_id) = qpath_res(cx, qpath, var.hir_id); if decl == local_id; then { let mut v = UsedVisitor { cx, id: decl, used: false, }; for s in block.stmts.iter().take(block.stmts.len()-1) { hir::intravisit::walk_stmt(&mut v, s); if v.used { return None; } } return Some(value); } } None } fn used_in_expr<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, id: hir::HirId, expr: &'tcx hir::Expr) -> bool { let mut v = UsedVisitor { cx, id, used: false }; hir::intravisit::walk_expr(&mut v, expr); v.used }