| use crate::utils::paths; |
| use crate::utils::{in_macro, iter_input_pats, match_type, method_chain_args, snippet, span_lint_and_then}; |
| use if_chain::if_chain; |
| use rustc::hir; |
| use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; |
| use rustc::ty::{self, Ty}; |
| use rustc::{declare_tool_lint, lint_array}; |
| use rustc_errors::Applicability; |
| use syntax::source_map::Span; |
| |
| #[derive(Clone)] |
| pub struct Pass; |
| |
| declare_clippy_lint! { |
| /// **What it does:** Checks for usage of `option.map(f)` where f is a function |
| /// or closure that returns the unit type. |
| /// |
| /// **Why is this bad?** Readability, this can be written more clearly with |
| /// an if let statement |
| /// |
| /// **Known problems:** None. |
| /// |
| /// **Example:** |
| /// |
| /// ```rust |
| /// let x: Option<&str> = do_stuff(); |
| /// x.map(log_err_msg); |
| /// x.map(|msg| log_err_msg(format_msg(msg))) |
| /// ``` |
| /// |
| /// The correct use would be: |
| /// |
| /// ```rust |
| /// let x: Option<&str> = do_stuff(); |
| /// if let Some(msg) = x { |
| /// log_err_msg(msg) |
| /// } |
| /// if let Some(msg) = x { |
| /// log_err_msg(format_msg(msg)) |
| /// } |
| /// ``` |
| pub OPTION_MAP_UNIT_FN, |
| complexity, |
| "using `option.map(f)`, where f is a function or closure that returns ()" |
| } |
| |
| declare_clippy_lint! { |
| /// **What it does:** Checks for usage of `result.map(f)` where f is a function |
| /// or closure that returns the unit type. |
| /// |
| /// **Why is this bad?** Readability, this can be written more clearly with |
| /// an if let statement |
| /// |
| /// **Known problems:** None. |
| /// |
| /// **Example:** |
| /// |
| /// ```rust |
| /// let x: Result<&str, &str> = do_stuff(); |
| /// x.map(log_err_msg); |
| /// x.map(|msg| log_err_msg(format_msg(msg))) |
| /// ``` |
| /// |
| /// The correct use would be: |
| /// |
| /// ```rust |
| /// let x: Result<&str, &str> = do_stuff(); |
| /// if let Ok(msg) = x { |
| /// log_err_msg(msg) |
| /// } |
| /// if let Ok(msg) = x { |
| /// log_err_msg(format_msg(msg)) |
| /// } |
| /// ``` |
| pub RESULT_MAP_UNIT_FN, |
| complexity, |
| "using `result.map(f)`, where f is a function or closure that returns ()" |
| } |
| |
| impl LintPass for Pass { |
| fn get_lints(&self) -> LintArray { |
| lint_array!(OPTION_MAP_UNIT_FN, RESULT_MAP_UNIT_FN) |
| } |
| |
| fn name(&self) -> &'static str { |
| "MapUnit" |
| } |
| } |
| |
| fn is_unit_type(ty: Ty<'_>) -> bool { |
| match ty.sty { |
| ty::Tuple(slice) => slice.is_empty(), |
| ty::Never => true, |
| _ => false, |
| } |
| } |
| |
| fn is_unit_function(cx: &LateContext<'_, '_>, expr: &hir::Expr) -> bool { |
| let ty = cx.tables.expr_ty(expr); |
| |
| if let ty::FnDef(id, _) = ty.sty { |
| if let Some(fn_type) = cx.tcx.fn_sig(id).no_bound_vars() { |
| return is_unit_type(fn_type.output()); |
| } |
| } |
| false |
| } |
| |
| fn is_unit_expression(cx: &LateContext<'_, '_>, expr: &hir::Expr) -> bool { |
| is_unit_type(cx.tables.expr_ty(expr)) |
| } |
| |
| /// The expression inside a closure may or may not have surrounding braces and |
| /// semicolons, which causes problems when generating a suggestion. Given an |
| /// expression that evaluates to '()' or '!', recursively remove useless braces |
| /// and semi-colons until is suitable for including in the suggestion template |
| fn reduce_unit_expression<'a>(cx: &LateContext<'_, '_>, expr: &'a hir::Expr) -> Option<Span> { |
| if !is_unit_expression(cx, expr) { |
| return None; |
| } |
| |
| match expr.node { |
| hir::ExprKind::Call(_, _) | hir::ExprKind::MethodCall(_, _, _) => { |
| // Calls can't be reduced any more |
| Some(expr.span) |
| }, |
| hir::ExprKind::Block(ref block, _) => { |
| match (&block.stmts[..], block.expr.as_ref()) { |
| (&[], Some(inner_expr)) => { |
| // If block only contains an expression, |
| // reduce `{ X }` to `X` |
| reduce_unit_expression(cx, inner_expr) |
| }, |
| (&[ref inner_stmt], None) => { |
| // If block only contains statements, |
| // reduce `{ X; }` to `X` or `X;` |
| match inner_stmt.node { |
| hir::StmtKind::Local(ref local) => Some(local.span), |
| hir::StmtKind::Expr(ref e) => Some(e.span), |
| hir::StmtKind::Semi(..) => Some(inner_stmt.span), |
| hir::StmtKind::Item(..) => None, |
| } |
| }, |
| _ => { |
| // For closures that contain multiple statements |
| // it's difficult to get a correct suggestion span |
| // for all cases (multi-line closures specifically) |
| // |
| // We do not attempt to build a suggestion for those right now. |
| None |
| }, |
| } |
| }, |
| _ => None, |
| } |
| } |
| |
| fn unit_closure<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'a hir::Expr) -> Option<(&'tcx hir::Arg, &'a hir::Expr)> { |
| if let hir::ExprKind::Closure(_, ref decl, inner_expr_id, _, _) = expr.node { |
| let body = cx.tcx.hir().body(inner_expr_id); |
| let body_expr = &body.value; |
| |
| if_chain! { |
| if decl.inputs.len() == 1; |
| if is_unit_expression(cx, body_expr); |
| if let Some(binding) = iter_input_pats(&decl, body).next(); |
| then { |
| return Some((binding, body_expr)); |
| } |
| } |
| } |
| None |
| } |
| |
| /// Builds a name for the let binding variable (`var_arg`) |
| /// |
| /// `x.field` => `x_field` |
| /// `y` => `_y` |
| /// |
| /// Anything else will return `_`. |
| fn let_binding_name(cx: &LateContext<'_, '_>, var_arg: &hir::Expr) -> String { |
| match &var_arg.node { |
| hir::ExprKind::Field(_, _) => snippet(cx, var_arg.span, "_").replace(".", "_"), |
| hir::ExprKind::Path(_) => format!("_{}", snippet(cx, var_arg.span, "")), |
| _ => "_".to_string(), |
| } |
| } |
| |
| fn suggestion_msg(function_type: &str, map_type: &str) -> String { |
| format!( |
| "called `map(f)` on an {0} value where `f` is a unit {1}", |
| map_type, function_type |
| ) |
| } |
| |
| fn lint_map_unit_fn(cx: &LateContext<'_, '_>, stmt: &hir::Stmt, expr: &hir::Expr, map_args: &[hir::Expr]) { |
| let var_arg = &map_args[0]; |
| |
| let (map_type, variant, lint) = if match_type(cx, cx.tables.expr_ty(var_arg), &paths::OPTION) { |
| ("Option", "Some", OPTION_MAP_UNIT_FN) |
| } else if match_type(cx, cx.tables.expr_ty(var_arg), &paths::RESULT) { |
| ("Result", "Ok", RESULT_MAP_UNIT_FN) |
| } else { |
| return; |
| }; |
| let fn_arg = &map_args[1]; |
| |
| if is_unit_function(cx, fn_arg) { |
| let msg = suggestion_msg("function", map_type); |
| let suggestion = format!( |
| "if let {0}({1}) = {2} {{ {3}(...) }}", |
| variant, |
| let_binding_name(cx, var_arg), |
| snippet(cx, var_arg.span, "_"), |
| snippet(cx, fn_arg.span, "_") |
| ); |
| |
| span_lint_and_then(cx, lint, expr.span, &msg, |db| { |
| db.span_suggestion(stmt.span, "try this", suggestion, Applicability::Unspecified); |
| }); |
| } else if let Some((binding, closure_expr)) = unit_closure(cx, fn_arg) { |
| let msg = suggestion_msg("closure", map_type); |
| |
| span_lint_and_then(cx, lint, expr.span, &msg, |db| { |
| if let Some(reduced_expr_span) = reduce_unit_expression(cx, closure_expr) { |
| let suggestion = format!( |
| "if let {0}({1}) = {2} {{ {3} }}", |
| variant, |
| snippet(cx, binding.pat.span, "_"), |
| snippet(cx, var_arg.span, "_"), |
| snippet(cx, reduced_expr_span, "_") |
| ); |
| db.span_suggestion( |
| stmt.span, |
| "try this", |
| suggestion, |
| Applicability::MachineApplicable, // snippet |
| ); |
| } else { |
| let suggestion = format!( |
| "if let {0}({1}) = {2} {{ ... }}", |
| variant, |
| snippet(cx, binding.pat.span, "_"), |
| snippet(cx, var_arg.span, "_") |
| ); |
| db.span_suggestion(stmt.span, "try this", suggestion, Applicability::Unspecified); |
| } |
| }); |
| } |
| } |
| |
| impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass { |
| fn check_stmt(&mut self, cx: &LateContext<'_, '_>, stmt: &hir::Stmt) { |
| if in_macro(stmt.span) { |
| return; |
| } |
| |
| if let hir::StmtKind::Semi(ref expr) = stmt.node { |
| if let Some(arglists) = method_chain_args(expr, &["map"]) { |
| lint_map_unit_fn(cx, stmt, expr, arglists[0]); |
| } |
| } |
| } |
| } |