5 use syntax::ast_util::{is_comparison_binop, binop_to_string};
6 use syntax::codemap::{Span, Spanned};
7 use syntax::visit::FnKind;
11 use utils::{match_path, snippet, snippet_block, span_lint, span_help_and_lint, walk_ptrs_ty};
13 /// Handles uncategorized lints
14 /// Currently handles linting of if-let-able matches
15 #[allow(missing_copy_implementations)]
19 declare_lint!(pub SINGLE_MATCH, Warn,
20 "a match statement with a single nontrivial arm (i.e, where the other arm \
21 is `_ => {}`) is used; recommends `if let` instead");
23 impl LintPass for MiscPass {
24 fn get_lints(&self) -> LintArray {
25 lint_array!(SINGLE_MATCH)
28 fn check_expr(&mut self, cx: &Context, expr: &Expr) {
29 if let ExprMatch(ref ex, ref arms, ast::MatchSource::Normal) = expr.node {
30 // check preconditions: only two arms
32 // both of the arms have a single pattern and no guard
33 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
34 arms[1].pats.len() == 1 && arms[1].guard.is_none() &&
35 // and the second pattern is a `_` wildcard: this is not strictly necessary,
36 // since the exhaustiveness check will ensure the last one is a catch-all,
37 // but in some cases, an explicit match is preferred to catch situations
38 // when an enum is extended, so we don't consider these cases
39 arms[1].pats[0].node == PatWild(PatWildSingle) &&
40 // finally, we don't want any content in the second arm (unit or empty block)
41 is_unit_expr(&*arms[1].body)
43 let body_code = snippet_block(cx, arms[0].body.span, "..");
44 let body_code = if let ExprBlock(_) = arms[0].body.node {
47 Cow::Owned(format!("{{ {} }}", body_code))
49 span_help_and_lint(cx, SINGLE_MATCH, expr.span,
50 "you seem to be trying to use match for \
51 destructuring a single pattern. Did you mean to \
53 &*format!("try\nif let {} = {} {}",
54 snippet(cx, arms[0].pats[0].span, ".."),
55 snippet(cx, ex.span, ".."),
63 fn is_unit_expr(expr: &Expr) -> bool {
65 ExprTup(ref v) if v.is_empty() => true,
66 ExprBlock(ref b) if b.stmts.is_empty() && b.expr.is_none() => true,
72 declare_lint!(pub TOPLEVEL_REF_ARG, Warn,
73 "a function argument is declared `ref` (i.e. `fn foo(ref x: u8)`, but not \
74 `fn foo((ref x, ref y): (u8, u8))`)");
76 #[allow(missing_copy_implementations)]
77 pub struct TopLevelRefPass;
79 impl LintPass for TopLevelRefPass {
80 fn get_lints(&self) -> LintArray {
81 lint_array!(TOPLEVEL_REF_ARG)
84 fn check_fn(&mut self, cx: &Context, k: FnKind, decl: &FnDecl, _: &Block, _: Span, _: NodeId) {
85 if let FnKind::FkFnBlock = k {
86 // Does not apply to closures
89 for ref arg in &decl.inputs {
90 if let PatIdent(BindByRef(_), _, _) = arg.pat.node {
94 "`ref` directly on a function argument is ignored. Consider using a reference type instead."
101 declare_lint!(pub CMP_NAN, Deny,
102 "comparisons to NAN (which will always return false, which is probably not intended)");
104 #[derive(Copy,Clone)]
107 impl LintPass for CmpNan {
108 fn get_lints(&self) -> LintArray {
112 fn check_expr(&mut self, cx: &Context, expr: &Expr) {
113 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
114 if is_comparison_binop(cmp.node) {
115 if let &ExprPath(_, ref path) = &left.node {
116 check_nan(cx, path, expr.span);
118 if let &ExprPath(_, ref path) = &right.node {
119 check_nan(cx, path, expr.span);
126 fn check_nan(cx: &Context, path: &Path, span: Span) {
127 path.segments.last().map(|seg| if seg.identifier.name == "NAN" {
128 span_lint(cx, CMP_NAN, span,
129 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead");
133 declare_lint!(pub FLOAT_CMP, Warn,
134 "using `==` or `!=` on float values (as floating-point operations \
135 usually involve rounding errors, it is always better to check for approximate \
136 equality within small bounds)");
138 #[derive(Copy,Clone)]
141 impl LintPass for FloatCmp {
142 fn get_lints(&self) -> LintArray {
143 lint_array!(FLOAT_CMP)
146 fn check_expr(&mut self, cx: &Context, expr: &Expr) {
147 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
149 if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
150 span_lint(cx, FLOAT_CMP, expr.span, &format!(
151 "{}-comparison of f32 or f64 detected. Consider changing this to \
152 `abs({} - {}) < epsilon` for some suitable value of epsilon",
153 binop_to_string(op), snippet(cx, left.span, ".."),
154 snippet(cx, right.span, "..")));
160 fn is_float(cx: &Context, expr: &Expr) -> bool {
161 if let ty::TyFloat(_) = walk_ptrs_ty(cx.tcx.expr_ty(expr)).sty {
168 declare_lint!(pub PRECEDENCE, Warn,
169 "expressions where precedence may trip up the unwary reader of the source; \
170 suggests adding parentheses, e.g. `x << 2 + y` will be parsed as `x << (2 + y)`");
172 #[derive(Copy,Clone)]
173 pub struct Precedence;
175 impl LintPass for Precedence {
176 fn get_lints(&self) -> LintArray {
177 lint_array!(PRECEDENCE)
180 fn check_expr(&mut self, cx: &Context, expr: &Expr) {
181 if let ExprBinary(Spanned { node: op, ..}, ref left, ref right) = expr.node {
182 if is_bit_op(op) && (is_arith_expr(left) || is_arith_expr(right)) {
183 span_lint(cx, PRECEDENCE, expr.span,
184 "operator precedence can trip the unwary. Consider adding parentheses \
185 to the subexpression");
191 fn is_arith_expr(expr : &Expr) -> bool {
193 ExprBinary(Spanned { node: op, ..}, _, _) => is_arith_op(op),
198 fn is_bit_op(op : BinOp_) -> bool {
200 BiBitXor | BiBitAnd | BiBitOr | BiShl | BiShr => true,
205 fn is_arith_op(op : BinOp_) -> bool {
207 BiAdd | BiSub | BiMul | BiDiv | BiRem => true,
212 declare_lint!(pub CMP_OWNED, Warn,
213 "creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`");
215 #[derive(Copy,Clone)]
218 impl LintPass for CmpOwned {
219 fn get_lints(&self) -> LintArray {
220 lint_array!(CMP_OWNED)
223 fn check_expr(&mut self, cx: &Context, expr: &Expr) {
224 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
225 if is_comparison_binop(cmp.node) {
226 check_to_owned(cx, left, right.span);
227 check_to_owned(cx, right, left.span)
233 fn check_to_owned(cx: &Context, expr: &Expr, other_span: Span) {
235 &ExprMethodCall(Spanned{node: ref ident, ..}, _, ref args) => {
236 let name = ident.name;
237 if name == "to_string" ||
238 name == "to_owned" && is_str_arg(cx, args) {
239 span_lint(cx, CMP_OWNED, expr.span, &format!(
240 "this creates an owned instance just for comparison. \
241 Consider using `{}.as_slice()` to compare without allocation",
242 snippet(cx, other_span, "..")))
245 &ExprCall(ref path, _) => {
246 if let &ExprPath(None, ref path) = &path.node {
247 if match_path(path, &["String", "from_str"]) ||
248 match_path(path, &["String", "from"]) {
249 span_lint(cx, CMP_OWNED, expr.span, &format!(
250 "this creates an owned instance just for comparison. \
251 Consider using `{}.as_slice()` to compare without allocation",
252 snippet(cx, other_span, "..")))
260 fn is_str_arg(cx: &Context, args: &[P<Expr>]) -> bool {
261 args.len() == 1 && if let ty::TyStr =
262 walk_ptrs_ty(cx.tcx.expr_ty(&*args[0])).sty { true } else { false }
265 declare_lint!(pub MODULO_ONE, Warn, "taking a number modulo 1, which always returns 0");
267 #[derive(Copy,Clone)]
268 pub struct ModuloOne;
270 impl LintPass for ModuloOne {
271 fn get_lints(&self) -> LintArray {
272 lint_array!(MODULO_ONE)
275 fn check_expr(&mut self, cx: &Context, expr: &Expr) {
276 if let ExprBinary(ref cmp, _, ref right) = expr.node {
277 if let &Spanned {node: BinOp_::BiRem, ..} = cmp {
278 if is_lit_one(right) {
279 cx.span_lint(MODULO_ONE, expr.span, "any number modulo 1 will be 0");
286 fn is_lit_one(expr: &Expr) -> bool {
287 if let ExprLit(ref spanned) = expr.node {
288 if let LitInt(1, _) = spanned.node {