rust-clippy/clippy_lints/src/question_mark.rs
2018-11-27 21:14:15 +01:00

149 lines
4.7 KiB
Rust

// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use crate::rustc::hir::def::Def;
use crate::rustc::hir::*;
use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use crate::rustc::{declare_tool_lint, lint_array};
use crate::syntax::ptr::P;
use crate::utils::sugg::Sugg;
use if_chain::if_chain;
use crate::rustc_errors::Applicability;
use crate::utils::paths::*;
use crate::utils::{match_def_path, match_type, span_lint_and_then};
/// **What it does:** Checks for expressions that could be replaced by the question mark operator
///
/// **Why is this bad?** Question mark usage is more idiomatic
///
/// **Known problems:** None
///
/// **Example:**
/// ```rust
/// if option.is_none() {
/// return None;
/// }
/// ```
///
/// Could be written:
///
/// ```rust
/// option?;
/// ```
declare_clippy_lint! {
pub QUESTION_MARK,
style,
"checks for expressions that could be replaced by the question mark operator"
}
#[derive(Copy, Clone)]
pub struct Pass;
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array!(QUESTION_MARK)
}
}
impl Pass {
/// Check if the given expression on the given context matches the following structure:
///
/// ```ignore
/// if option.is_none() {
/// return None;
/// }
/// ```
///
/// If it matches, it will suggest to use the question mark operator instead
fn check_is_none_and_early_return_none(cx: &LateContext<'_, '_>, expr: &Expr) {
if_chain! {
if let ExprKind::If(ref if_expr, ref body, _) = expr.node;
if let ExprKind::MethodCall(ref segment, _, ref args) = if_expr.node;
if segment.ident.name == "is_none";
if Self::expression_returns_none(cx, body);
if let Some(subject) = args.get(0);
if Self::is_option(cx, subject);
then {
span_lint_and_then(
cx,
QUESTION_MARK,
expr.span,
"this block may be rewritten with the `?` operator",
|db| {
let receiver_str = &Sugg::hir(cx, subject, "..");
db.span_suggestion_with_applicability(
expr.span,
"replace_it_with",
format!("{}?;", receiver_str),
Applicability::MachineApplicable, // snippet
);
}
)
}
}
}
fn is_option(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
let expr_ty = cx.tables.expr_ty(expression);
match_type(cx, expr_ty, &OPTION)
}
fn expression_returns_none(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
match expression.node {
ExprKind::Block(ref block, _) => {
if let Some(return_expression) = Self::return_expression(block) {
return Self::expression_returns_none(cx, &return_expression);
}
false
},
ExprKind::Ret(Some(ref expr)) => Self::expression_returns_none(cx, expr),
ExprKind::Path(ref qp) => {
if let Def::VariantCtor(def_id, _) = cx.tables.qpath_def(qp, expression.hir_id) {
return match_def_path(cx.tcx, def_id, &OPTION_NONE);
}
false
},
_ => false,
}
}
fn return_expression(block: &Block) -> Option<P<Expr>> {
// Check if last expression is a return statement. Then, return the expression
if_chain! {
if block.stmts.len() == 1;
if let Some(expr) = block.stmts.iter().last();
if let StmtKind::Semi(ref expr, _) = expr.node;
if let ExprKind::Ret(ref ret_expr) = expr.node;
if let &Some(ref ret_expr) = ret_expr;
then {
return Some(ret_expr.clone());
}
}
// Check if the block has an implicit return expression
if let Some(ref ret_expr) = block.expr {
return Some(ret_expr.clone());
}
None
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
Self::check_is_none_and_early_return_none(cx, expr);
}
}