| use crate::utils::{higher, qpath_res, snippet, span_lint_and_then}; |
| use if_chain::if_chain; |
| use rustc::hir; |
| use rustc::hir::def::Res; |
| use rustc::hir::BindingAnnotation; |
| use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; |
| use rustc::{declare_lint_pass, declare_tool_lint}; |
| use rustc_errors::Applicability; |
| |
| 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 => "<mut> ", |
| _ => "", |
| }; |
| |
| // 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, "<value>"), |
| default=snippet(cx, default.span, "<default>"), |
| ); |
| 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 |
| } |