rust-clippy/src/misc.rs

use syntax::ptr::P;
use syntax::ast;
use syntax::ast::*;
use syntax::ast_util::{is_comparison_binop, binop_to_string};
use syntax::visit::{FnKind};
use rustc::lint::{Context, LintPass, LintArray, Lint, Level};
use rustc::middle::ty;
use syntax::codemap::{Span, Spanned};

use utils::{match_path, snippet, span_lint, span_help_and_lint};

pub fn walk_ty<'t>(ty: ty::Ty<'t>) -> ty::Ty<'t> {
    match ty.sty {
        ty::TyRef(_, ref tm) | ty::TyRawPtr(ref tm) => walk_ty(tm.ty),
        _ => ty
    }
}

/// Handles uncategorized lints
/// Currently handles linting of if-let-able matches
#[allow(missing_copy_implementations)]
pub struct MiscPass;


declare_lint!(pub SINGLE_MATCH, Warn,
              "Warn on usage of matches with a single nontrivial arm");

impl LintPass for MiscPass {
    fn get_lints(&self) -> LintArray {
        lint_array!(SINGLE_MATCH)
    }

    fn check_expr(&mut self, cx: &Context, expr: &Expr) {
        if let ExprMatch(ref ex, ref arms, ast::MatchSource::Normal) = expr.node {
            if arms.len() == 2 {
                if arms[0].guard.is_none() && arms[1].pats.len() == 1 {
                    match arms[1].body.node {
                        ExprTup(ref v) if v.is_empty() && arms[1].guard.is_none() => (),
                        ExprBlock(ref b) if b.stmts.is_empty() && arms[1].guard.is_none() => (),
                         _ => return
                    }
                    // In some cases, an exhaustive match is preferred to catch situations when
                    // an enum is extended. So we only consider cases where a `_` wildcard is used
                    if arms[1].pats[0].node == PatWild(PatWildSingle) &&
                            arms[0].pats.len() == 1 {
                        let body_code = snippet(cx, arms[0].body.span, "..");
                        let suggestion = if let ExprBlock(_) = arms[0].body.node {
                            body_code.into_owned()
                        } else {
                            format!("{{ {} }}", body_code)
                        };
                        span_help_and_lint(cx, SINGLE_MATCH, expr.span,
                              "You seem to be trying to use match for \
                              destructuring a single pattern. Did you mean to \
                              use `if let`?",
                              &*format!("Try\nif let {} = {} {}",
                                        snippet(cx, arms[0].pats[0].span, ".."),
                                        snippet(cx, ex.span, ".."),
                                        suggestion)
                        );
                    }
                }
            }
        }
    }
}


declare_lint!(pub STR_TO_STRING, Warn, "Warn when a String could use to_owned() instead of to_string()");

#[allow(missing_copy_implementations)]
pub struct StrToStringPass;

impl LintPass for StrToStringPass {
    fn get_lints(&self) -> LintArray {
        lint_array!(STR_TO_STRING)
    }

    fn check_expr(&mut self, cx: &Context, expr: &ast::Expr) {
        match expr.node {
            ast::ExprMethodCall(ref method, _, ref args)
                if method.node.name == "to_string"
                && is_str(cx, &*args[0]) => {
                span_lint(cx, STR_TO_STRING, expr.span, "str.to_owned() is faster");
            },
            _ => ()
        }

        fn is_str(cx: &Context, expr: &ast::Expr) -> bool {
            match walk_ty(cx.tcx.expr_ty(expr)).sty {
                ty::TyStr => true,
                _ => false
            }
        }
    }
}


declare_lint!(pub TOPLEVEL_REF_ARG, Warn, "Warn about pattern matches with top-level `ref` bindings");

#[allow(missing_copy_implementations)]
pub struct TopLevelRefPass;

impl LintPass for TopLevelRefPass {
    fn get_lints(&self) -> LintArray {
        lint_array!(TOPLEVEL_REF_ARG)
    }

    fn check_fn(&mut self, cx: &Context, _: FnKind, decl: &FnDecl, _: &Block, _: Span, _: NodeId) {
        for ref arg in decl.inputs.iter() {
            if let PatIdent(BindByRef(_), _, _) = arg.pat.node {
                span_lint(cx,
                    TOPLEVEL_REF_ARG,
                    arg.pat.span,
                    "`ref` directly on a function argument is ignored. Have you considered using a reference type instead?"
                );
            }
        }
    }
}

declare_lint!(pub CMP_NAN, Deny, "Deny comparisons to std::f32::NAN or std::f64::NAN");

#[derive(Copy,Clone)]
pub struct CmpNan;

impl LintPass for CmpNan {
    fn get_lints(&self) -> LintArray {
        lint_array!(CMP_NAN)
    }

    fn check_expr(&mut self, cx: &Context, expr: &Expr) {
        if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
            if is_comparison_binop(cmp.node) {
                if let &ExprPath(_, ref path) = &left.node {
                    check_nan(cx, path, expr.span);
                }
                if let &ExprPath(_, ref path) = &right.node {
                    check_nan(cx, path, expr.span);
                }
            }
        }
    }
}

fn check_nan(cx: &Context, path: &Path, span: Span) {
    path.segments.last().map(|seg| if seg.identifier.name == "NAN" {
        span_lint(cx, CMP_NAN, span,
                  "Doomed comparison with NAN, use std::{f32,f64}::is_nan instead");
    });
}

declare_lint!(pub FLOAT_CMP, Warn,
              "Warn on ==/!= comparison of floaty values");

#[derive(Copy,Clone)]
pub struct FloatCmp;

impl LintPass for FloatCmp {
    fn get_lints(&self) -> LintArray {
        lint_array!(FLOAT_CMP)
    }

    fn check_expr(&mut self, cx: &Context, expr: &Expr) {
        if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
            let op = cmp.node;
            if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
                span_lint(cx, FLOAT_CMP, expr.span, &format!(
                    "{}-Comparison of f32 or f64 detected. You may want to change this to 'abs({} - {}) < epsilon' for some suitable value of epsilon",
                    binop_to_string(op), snippet(cx, left.span, ".."),
                    snippet(cx, right.span, "..")));
            }
        }
    }
}

fn is_float(cx: &Context, expr: &Expr) -> bool {
    if let ty::TyFloat(_) = walk_ty(cx.tcx.expr_ty(expr)).sty {
        true
    } else {
        false
    }
}

declare_lint!(pub PRECEDENCE, Warn,
              "Warn on mixing bit ops with integer arithmetic without parenthesis");

#[derive(Copy,Clone)]
pub struct Precedence;

impl LintPass for Precedence {
    fn get_lints(&self) -> LintArray {
        lint_array!(PRECEDENCE)
    }

    fn check_expr(&mut self, cx: &Context, expr: &Expr) {
        if let ExprBinary(Spanned { node: op, ..}, ref left, ref right) = expr.node {
            if is_bit_op(op) && (is_arith_expr(left) || is_arith_expr(right)) {
                span_lint(cx, PRECEDENCE, expr.span,
                    "Operator precedence can trip the unwary. Consider adding parenthesis to the subexpression.");
            }
        }
    }
}

fn is_arith_expr(expr : &Expr) -> bool {
    match expr.node {
        ExprBinary(Spanned { node: op, ..}, _, _) => is_arith_op(op),
        _ => false
    }
}

fn is_bit_op(op : BinOp_) -> bool {
    match op {
        BiBitXor | BiBitAnd | BiBitOr | BiShl | BiShr => true,
        _ => false
    }
}

fn is_arith_op(op : BinOp_) -> bool {
    match op {
        BiAdd | BiSub | BiMul | BiDiv | BiRem => true,
        _ => false
    }
}

declare_lint!(pub CMP_OWNED, Warn,
              "Warn on creating an owned string just for comparison");

#[derive(Copy,Clone)]
pub struct CmpOwned;

impl LintPass for CmpOwned {
    fn get_lints(&self) -> LintArray {
        lint_array!(CMP_OWNED)
    }

    fn check_expr(&mut self, cx: &Context, expr: &Expr) {
        if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
            if is_comparison_binop(cmp.node) {
                check_to_owned(cx, left, right.span);
                check_to_owned(cx, right, left.span)
            }
        }
    }
}

fn check_to_owned(cx: &Context, expr: &Expr, other_span: Span) {
    match &expr.node {
        &ExprMethodCall(Spanned{node: ref ident, ..}, _, ref args) => {
            let name = ident.name;
            if name == "to_string" ||
                name == "to_owned" && is_str_arg(cx, args) {
                    span_lint(cx, CMP_OWNED, expr.span, &format!(
                        "this creates an owned instance just for comparison. \
                         Consider using {}.as_slice() to compare without allocation",
                        snippet(cx, other_span, "..")))
                }
        },
        &ExprCall(ref path, _) => {
            if let &ExprPath(None, ref path) = &path.node {
                if match_path(path, &["String", "from_str"]) ||
                    match_path(path, &["String", "from"]) {
                        span_lint(cx, CMP_OWNED, expr.span, &format!(
                            "this creates an owned instance just for comparison. \
                             Consider using {}.as_slice() to compare without allocation",
                            snippet(cx, other_span, "..")))
                    }
            }
        },
        _ => ()
    }
}

fn is_str_arg(cx: &Context, args: &[P<Expr>]) -> bool {
    args.len() == 1 && if let ty::TyStr =
        walk_ty(cx.tcx.expr_ty(&*args[0])).sty { true } else { false }
}

declare_lint!(pub NEEDLESS_RETURN, Warn,
              "Warn on using a return statement where an expression would be enough");

#[derive(Copy,Clone)]
pub struct NeedlessReturn;

impl NeedlessReturn {
    // Check the final stmt or expr in a block for unnecessary return.
    fn check_block_return(&mut self, cx: &Context, block: &Block) {
        if let Some(ref expr) = block.expr {
            self.check_final_expr(cx, expr);
        } else if let Some(stmt) = block.stmts.last() {
            if let StmtSemi(ref expr, _) = stmt.node {
                if let ExprRet(Some(ref inner)) = expr.node {
                    self.emit_lint(cx, (expr.span, inner.span));
                }
            }
        }
    }

    // Check a the final expression in a block if it's a return.
    fn check_final_expr(&mut self, cx: &Context, expr: &Expr) {
        match expr.node {
            // simple return is always "bad"
            ExprRet(Some(ref inner)) => {
                self.emit_lint(cx, (expr.span, inner.span));
            }
            // a whole block? check it!
            ExprBlock(ref block) => {
                self.check_block_return(cx, block);
            }
            // an if/if let expr, check both exprs
            // note, if without else is going to be a type checking error anyways
            // (except for unit type functions) so we don't match it
            ExprIf(_, ref ifblock, Some(ref elsexpr)) |
            ExprIfLet(_, _, ref ifblock, Some(ref elsexpr)) => {
                self.check_block_return(cx, ifblock);
                self.check_final_expr(cx, elsexpr);
            }
            // a match expr, check all arms
            ExprMatch(_, ref arms, _) => {
                for arm in arms {
                    self.check_final_expr(cx, &*arm.body);
                }
            }
            _ => { }
        }
    }

    fn emit_lint(&mut self, cx: &Context, spans: (Span, Span)) {
        span_lint(cx, NEEDLESS_RETURN, spans.0, &format!(
            "unneeded return statement. Consider using {} \
             without the trailing semicolon",
            snippet(cx, spans.1, "..")))
    }
}

impl LintPass for NeedlessReturn {
    fn get_lints(&self) -> LintArray {
        lint_array!(NEEDLESS_RETURN)
    }

    fn check_fn(&mut self, cx: &Context, _: FnKind, _: &FnDecl,
                block: &Block, _: Span, _: ast::NodeId) {
        self.check_block_return(cx, block);
    }
}


declare_lint!(pub MODULO_ONE, Warn, "Warn on expressions that include % 1, which is always 0");

#[derive(Copy,Clone)]
pub struct ModuloOne;

impl LintPass for ModuloOne {
    fn get_lints(&self) -> LintArray {
        lint_array!(MODULO_ONE)
    }

    fn check_expr(&mut self, cx: &Context, expr: &Expr) {
        if let ExprBinary(ref cmp, _, ref right) = expr.node {
            if let &Spanned {node: BinOp_::BiRem, ..} = cmp {
                if is_lit_one(right) {
                    cx.span_lint(MODULO_ONE, expr.span, "Any number modulo 1 will be 0");
                }
            }
        }
    }
}

fn is_lit_one(expr: &Expr) -> bool {
    if let ExprLit(ref spanned) = expr.node {
        if let LitInt(1, _) = spanned.node {
            return true;
        }
    }
    false
}