rust/clippy_lints/src/question_mark.rs
2020-01-13 21:55:57 +09:00

163 lines
5.6 KiB
Rust

use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::*;
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use crate::utils::paths::*;
use crate::utils::sugg::Sugg;
use crate::utils::{higher, match_def_path, match_type, span_lint_and_then, SpanlessEq};
declare_clippy_lint! {
/// **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:**
/// ```ignore
/// if option.is_none() {
/// return None;
/// }
/// ```
///
/// Could be written:
///
/// ```ignore
/// option?;
/// ```
pub QUESTION_MARK,
style,
"checks for expressions that could be replaced by the question mark operator"
}
declare_lint_pass!(QuestionMark => [QUESTION_MARK]);
impl QuestionMark {
/// Checks 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 Some((if_expr, body, else_)) = higher::if_block(&expr);
if let ExprKind::MethodCall(segment, _, args) = &if_expr.kind;
if segment.ident.name == sym!(is_none);
if Self::expression_returns_none(cx, body);
if let Some(subject) = args.get(0);
if Self::is_option(cx, subject);
then {
let receiver_str = &Sugg::hir(cx, subject, "..");
let mut replacement: Option<String> = None;
if let Some(else_) = else_ {
if_chain! {
if let ExprKind::Block(block, None) = &else_.kind;
if block.stmts.is_empty();
if let Some(block_expr) = &block.expr;
if SpanlessEq::new(cx).ignore_fn().eq_expr(subject, block_expr);
then {
replacement = Some(format!("Some({}?)", receiver_str));
}
}
} else if Self::moves_by_default(cx, subject) {
replacement = Some(format!("{}.as_ref()?;", receiver_str));
} else {
replacement = Some(format!("{}?;", receiver_str));
}
if let Some(replacement_str) = replacement {
span_lint_and_then(
cx,
QUESTION_MARK,
expr.span,
"this block may be rewritten with the `?` operator",
|db| {
db.span_suggestion(
expr.span,
"replace_it_with",
replacement_str,
Applicability::MaybeIncorrect, // snippet
);
}
)
}
}
}
}
fn moves_by_default(cx: &LateContext<'_, '_>, expression: &Expr<'_>) -> bool {
let expr_ty = cx.tables.expr_ty(expression);
!expr_ty.is_copy_modulo_regions(cx.tcx, cx.param_env, expression.span)
}
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.kind {
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 Res::Def(DefKind::Ctor(def::CtorOf::Variant, def::CtorKind::Const), def_id) =
cx.tables.qpath_res(qp, expression.hir_id)
{
return match_def_path(cx, def_id, &OPTION_NONE);
}
false
},
_ => false,
}
}
fn return_expression<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
// 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.kind;
if let ExprKind::Ret(ret_expr) = expr.kind;
if let Some(ret_expr) = ret_expr;
then {
return Some(ret_expr);
}
}
// Check for `return` without a semicolon.
if_chain! {
if block.stmts.is_empty();
if let Some(ExprKind::Ret(Some(ret_expr))) = block.expr.as_ref().map(|e| &e.kind);
then {
return Some(ret_expr);
}
}
None
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for QuestionMark {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
Self::check_is_none_and_early_return_none(cx, expr);
}
}