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};
14 /// Handles uncategorized lints
15 /// Currently handles linting of if-let-able matches
16 #[allow(missing_copy_implementations)]
20 declare_lint!(pub SINGLE_MATCH, Warn,
21 "a match statement with a single nontrivial arm (i.e, where the other arm \
22 is `_ => {}`) is used; recommends `if let` instead");
24 impl LintPass for MiscPass {
25 fn get_lints(&self) -> LintArray {
26 lint_array!(SINGLE_MATCH)
29 fn check_expr(&mut self, cx: &Context, expr: &Expr) {
30 if let ExprMatch(ref ex, ref arms, ast::MatchSource::Normal) = expr.node {
31 // check preconditions: only two arms
33 // both of the arms have a single pattern and no guard
34 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
35 arms[1].pats.len() == 1 && arms[1].guard.is_none() &&
36 // and the second pattern is a `_` wildcard: this is not strictly necessary,
37 // since the exhaustiveness check will ensure the last one is a catch-all,
38 // but in some cases, an explicit match is preferred to catch situations
39 // when an enum is extended, so we don't consider these cases
40 arms[1].pats[0].node == PatWild(PatWildSingle) &&
41 // finally, we don't want any content in the second arm (unit or empty block)
42 is_unit_expr(&*arms[1].body)
44 let body_code = snippet_block(cx, arms[0].body.span, "..");
45 let body_code = if let ExprBlock(_) = arms[0].body.node {
48 Cow::Owned(format!("{{ {} }}", body_code))
50 span_help_and_lint(cx, SINGLE_MATCH, expr.span,
51 "you seem to be trying to use match for \
52 destructuring a single pattern. Did you mean to \
54 &*format!("try\nif let {} = {} {}",
55 snippet(cx, arms[0].pats[0].span, ".."),
56 snippet(cx, ex.span, ".."),
64 fn is_unit_expr(expr: &Expr) -> bool {
66 ExprTup(ref v) if v.is_empty() => true,
67 ExprBlock(ref b) if b.stmts.is_empty() && b.expr.is_none() => true,
73 declare_lint!(pub TOPLEVEL_REF_ARG, Warn,
74 "a function argument is declared `ref` (i.e. `fn foo(ref x: u8)`, but not \
75 `fn foo((ref x, ref y): (u8, u8))`)");
77 #[allow(missing_copy_implementations)]
78 pub struct TopLevelRefPass;
80 impl LintPass for TopLevelRefPass {
81 fn get_lints(&self) -> LintArray {
82 lint_array!(TOPLEVEL_REF_ARG)
85 fn check_fn(&mut self, cx: &Context, k: FnKind, decl: &FnDecl, _: &Block, _: Span, _: NodeId) {
86 if let FnKind::FkFnBlock = k {
87 // Does not apply to closures
90 for ref arg in &decl.inputs {
91 if let PatIdent(BindByRef(_), _, _) = arg.pat.node {
95 "`ref` directly on a function argument is ignored. Consider using a reference type instead."
102 declare_lint!(pub CMP_NAN, Deny,
103 "comparisons to NAN (which will always return false, which is probably not intended)");
105 #[derive(Copy,Clone)]
108 impl LintPass for CmpNan {
109 fn get_lints(&self) -> LintArray {
113 fn check_expr(&mut self, cx: &Context, expr: &Expr) {
114 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
115 if is_comparison_binop(cmp.node) {
116 if let &ExprPath(_, ref path) = &left.node {
117 check_nan(cx, path, expr.span);
119 if let &ExprPath(_, ref path) = &right.node {
120 check_nan(cx, path, expr.span);
127 fn check_nan(cx: &Context, path: &Path, span: Span) {
128 path.segments.last().map(|seg| if seg.identifier.name == "NAN" {
129 span_lint(cx, CMP_NAN, span,
130 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead");
134 declare_lint!(pub FLOAT_CMP, Warn,
135 "using `==` or `!=` on float values (as floating-point operations \
136 usually involve rounding errors, it is always better to check for approximate \
137 equality within small bounds)");
139 #[derive(Copy,Clone)]
142 impl LintPass for FloatCmp {
143 fn get_lints(&self) -> LintArray {
144 lint_array!(FLOAT_CMP)
147 fn check_expr(&mut self, cx: &Context, expr: &Expr) {
148 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
150 if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
151 if constant(cx, left).or_else(|| constant(cx, right)).map_or(
152 false, |c| c.as_float().map_or(false, |f| f == 0.0)) {
155 span_lint(cx, FLOAT_CMP, expr.span, &format!(
156 "{}-comparison of f32 or f64 detected. Consider changing this to \
157 `abs({} - {}) < epsilon` for some suitable value of epsilon",
158 binop_to_string(op), snippet(cx, left.span, ".."),
159 snippet(cx, right.span, "..")));
165 fn is_float(cx: &Context, expr: &Expr) -> bool {
166 if let ty::TyFloat(_) = walk_ptrs_ty(cx.tcx.expr_ty(expr)).sty {
173 declare_lint!(pub PRECEDENCE, Warn,
174 "expressions where precedence may trip up the unwary reader of the source; \
175 suggests adding parentheses, e.g. `x << 2 + y` will be parsed as `x << (2 + y)`");
177 #[derive(Copy,Clone)]
178 pub struct Precedence;
180 impl LintPass for Precedence {
181 fn get_lints(&self) -> LintArray {
182 lint_array!(PRECEDENCE)
185 fn check_expr(&mut self, cx: &Context, expr: &Expr) {
186 if let ExprBinary(Spanned { node: op, ..}, ref left, ref right) = expr.node {
187 if is_bit_op(op) && (is_arith_expr(left) || is_arith_expr(right)) {
188 span_lint(cx, PRECEDENCE, expr.span,
189 "operator precedence can trip the unwary. Consider adding parentheses \
190 to the subexpression");
196 fn is_arith_expr(expr : &Expr) -> bool {
198 ExprBinary(Spanned { node: op, ..}, _, _) => is_arith_op(op),
203 fn is_bit_op(op : BinOp_) -> bool {
205 BiBitXor | BiBitAnd | BiBitOr | BiShl | BiShr => true,
210 fn is_arith_op(op : BinOp_) -> bool {
212 BiAdd | BiSub | BiMul | BiDiv | BiRem => true,
217 declare_lint!(pub CMP_OWNED, Warn,
218 "creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`");
220 #[derive(Copy,Clone)]
223 impl LintPass for CmpOwned {
224 fn get_lints(&self) -> LintArray {
225 lint_array!(CMP_OWNED)
228 fn check_expr(&mut self, cx: &Context, expr: &Expr) {
229 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
230 if is_comparison_binop(cmp.node) {
231 check_to_owned(cx, left, right.span);
232 check_to_owned(cx, right, left.span)
238 fn check_to_owned(cx: &Context, expr: &Expr, other_span: Span) {
240 &ExprMethodCall(Spanned{node: ref ident, ..}, _, ref args) => {
241 let name = ident.name;
242 if name == "to_string" ||
243 name == "to_owned" && is_str_arg(cx, args) {
244 span_lint(cx, CMP_OWNED, expr.span, &format!(
245 "this creates an owned instance just for comparison. \
246 Consider using `{}.as_slice()` to compare without allocation",
247 snippet(cx, other_span, "..")))
250 &ExprCall(ref path, _) => {
251 if let &ExprPath(None, ref path) = &path.node {
252 if match_path(path, &["String", "from_str"]) ||
253 match_path(path, &["String", "from"]) {
254 span_lint(cx, CMP_OWNED, expr.span, &format!(
255 "this creates an owned instance just for comparison. \
256 Consider using `{}.as_slice()` to compare without allocation",
257 snippet(cx, other_span, "..")))
265 fn is_str_arg(cx: &Context, args: &[P<Expr>]) -> bool {
266 args.len() == 1 && if let ty::TyStr =
267 walk_ptrs_ty(cx.tcx.expr_ty(&*args[0])).sty { true } else { false }
270 declare_lint!(pub MODULO_ONE, Warn, "taking a number modulo 1, which always returns 0");
272 #[derive(Copy,Clone)]
273 pub struct ModuloOne;
275 impl LintPass for ModuloOne {
276 fn get_lints(&self) -> LintArray {
277 lint_array!(MODULO_ONE)
280 fn check_expr(&mut self, cx: &Context, expr: &Expr) {
281 if let ExprBinary(ref cmp, _, ref right) = expr.node {
282 if let &Spanned {node: BinOp_::BiRem, ..} = cmp {
283 if is_lit_one(right) {
284 cx.span_lint(MODULO_ONE, expr.span, "any number modulo 1 will be 0");
291 fn is_lit_one(expr: &Expr) -> bool {
292 if let ExprLit(ref spanned) = expr.node {
293 if let LitInt(1, _) = spanned.node {