| use crate::utils::{is_type_diagnostic_item, iter_input_pats, method_chain_args, snippet, span_lint_and_then}; |
| use if_chain::if_chain; |
| use rustc_errors::Applicability; |
| use rustc_hir as hir; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_middle::ty::{self, Ty}; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| use rustc_span::source_map::Span; |
| |
| 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 |
| /// # fn do_stuff() -> Option<String> { Some(String::new()) } |
| /// # fn log_err_msg(foo: String) -> Option<String> { Some(foo) } |
| /// # fn format_msg(foo: String) -> String { String::new() } |
| /// let x: Option<String> = do_stuff(); |
| /// x.map(log_err_msg); |
| /// # let x: Option<String> = do_stuff(); |
| /// x.map(|msg| log_err_msg(format_msg(msg))); |
| /// ``` |
| /// |
| /// The correct use would be: |
| /// |
| /// ```rust |
| /// # fn do_stuff() -> Option<String> { Some(String::new()) } |
| /// # fn log_err_msg(foo: String) -> Option<String> { Some(foo) } |
| /// # fn format_msg(foo: String) -> String { String::new() } |
| /// let x: Option<String> = do_stuff(); |
| /// if let Some(msg) = x { |
| /// log_err_msg(msg); |
| /// } |
| /// |
| /// # let x: Option<String> = do_stuff(); |
| /// 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 |
| /// # fn do_stuff() -> Result<String, String> { Ok(String::new()) } |
| /// # fn log_err_msg(foo: String) -> Result<String, String> { Ok(foo) } |
| /// # fn format_msg(foo: String) -> String { String::new() } |
| /// let x: Result<String, String> = do_stuff(); |
| /// x.map(log_err_msg); |
| /// # let x: Result<String, String> = do_stuff(); |
| /// x.map(|msg| log_err_msg(format_msg(msg))); |
| /// ``` |
| /// |
| /// The correct use would be: |
| /// |
| /// ```rust |
| /// # fn do_stuff() -> Result<String, String> { Ok(String::new()) } |
| /// # fn log_err_msg(foo: String) -> Result<String, String> { Ok(foo) } |
| /// # fn format_msg(foo: String) -> String { String::new() } |
| /// let x: Result<String, String> = do_stuff(); |
| /// if let Ok(msg) = x { |
| /// log_err_msg(msg); |
| /// }; |
| /// # let x: Result<String, String> = do_stuff(); |
| /// 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 `()`" |
| } |
| |
| declare_lint_pass!(MapUnit => [OPTION_MAP_UNIT_FN, RESULT_MAP_UNIT_FN]); |
| |
| fn is_unit_type(ty: Ty<'_>) -> bool { |
| match ty.kind { |
| 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.kind { |
| 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.kind { |
| 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.kind { |
| 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<'tcx>( |
| cx: &LateContext<'tcx>, |
| expr: &hir::Expr<'_>, |
| ) -> Option<(&'tcx hir::Param<'tcx>, &'tcx hir::Expr<'tcx>)> { |
| if let hir::ExprKind::Closure(_, ref decl, inner_expr_id, _, _) = expr.kind { |
| 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 `a`. |
| fn let_binding_name(cx: &LateContext<'_>, var_arg: &hir::Expr<'_>) -> String { |
| match &var_arg.kind { |
| hir::ExprKind::Field(_, _) => snippet(cx, var_arg.span, "_").replace(".", "_"), |
| hir::ExprKind::Path(_) => format!("_{}", snippet(cx, var_arg.span, "")), |
| _ => "a".to_string(), |
| } |
| } |
| |
| #[must_use] |
| fn suggestion_msg(function_type: &str, map_type: &str) -> String { |
| format!( |
| "called `map(f)` on an `{0}` value where `f` is a {1} that returns the unit type", |
| 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 is_type_diagnostic_item(cx, cx.tables().expr_ty(var_arg), sym!(option_type)) { |
| ("Option", "Some", OPTION_MAP_UNIT_FN) |
| } else if is_type_diagnostic_item(cx, cx.tables().expr_ty(var_arg), sym!(result_type)) { |
| ("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}({binding}) = {1} {{ {2}({binding}) }}", |
| variant, |
| snippet(cx, var_arg.span, "_"), |
| snippet(cx, fn_arg.span, "_"), |
| binding = let_binding_name(cx, var_arg) |
| ); |
| |
| span_lint_and_then(cx, lint, expr.span, &msg, |diag| { |
| diag.span_suggestion(stmt.span, "try this", suggestion, Applicability::MachineApplicable); |
| }); |
| } 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, |diag| { |
| 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, "_") |
| ); |
| diag.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, "_"), |
| ); |
| diag.span_suggestion(stmt.span, "try this", suggestion, Applicability::HasPlaceholders); |
| } |
| }); |
| } |
| } |
| |
| impl<'tcx> LateLintPass<'tcx> for MapUnit { |
| fn check_stmt(&mut self, cx: &LateContext<'_>, stmt: &hir::Stmt<'_>) { |
| if stmt.span.from_expansion() { |
| return; |
| } |
| |
| if let hir::StmtKind::Semi(ref expr) = stmt.kind { |
| if let Some(arglists) = method_chain_args(expr, &["map"]) { |
| lint_map_unit_fn(cx, stmt, expr, arglists[0]); |
| } |
| } |
| } |
| } |