rust/clippy_lints/src/question_mark.rs
2018-03-28 15:24:26 +02:00

139 lines
4.0 KiB
Rust

use rustc::lint::*;
use rustc::hir::*;
use rustc::hir::def::Def;
use utils::sugg::Sugg;
use syntax::ptr::P;
use utils::{match_def_path, match_type, span_lint_and_then};
use utils::paths::*;
/// **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 QuestionMarkPass;
impl LintPass for QuestionMarkPass {
fn get_lints(&self) -> LintArray {
lint_array!(QUESTION_MARK)
}
}
impl QuestionMarkPass {
/// Check if the given expression on the given context matches the following structure:
///
/// ```
/// 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 ExprIf(ref if_expr, ref body, _) = expr.node;
if let ExprMethodCall(ref segment, _, ref args) = if_expr.node;
if segment.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(
expr.span,
"replace_it_with",
format!("{}?;", receiver_str),
);
}
)
}
}
}
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 {
ExprBlock(ref block) => {
if let Some(return_expression) = Self::return_expression(block) {
return Self::expression_returns_none(cx, &return_expression);
}
false
},
ExprRet(Some(ref expr)) => {
Self::expression_returns_none(cx, expr)
},
ExprPath(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 StmtSemi(ref expr, _) = expr.node;
if let ExprRet(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 QuestionMarkPass {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
Self::check_is_none_and_early_return_none(cx, expr);
}
}