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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::is_lang_ctor;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::sugg::Sugg;
use clippy_utils::ty::is_type_diagnostic_item;
use clippy_utils::{eq_expr_value, path_to_local_id};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::LangItem::{OptionNone, OptionSome};
use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, MatchSource, PatKind, StmtKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
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 ExprKind::If(if_expr, body, else_) = &expr.kind;
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 mut applicability = Applicability::MachineApplicable;
let receiver_str = &Sugg::hir_with_applicability(cx, subject, "..", &mut applicability);
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 eq_expr_value(cx, subject, block_expr);
then {
replacement = Some(format!("Some({}?)", receiver_str));
}
}
} else if Self::moves_by_default(cx, subject)
&& !matches!(subject.kind, ExprKind::Call(..) | ExprKind::MethodCall(..))
{
replacement = Some(format!("{}.as_ref()?;", receiver_str));
} else {
replacement = Some(format!("{}?;", receiver_str));
}
if let Some(replacement_str) = replacement {
span_lint_and_sugg(
cx,
QUESTION_MARK,
expr.span,
"this block may be rewritten with the `?` operator",
"replace it with",
replacement_str,
applicability,
);
}
}
}
}
fn check_if_let_some_and_early_return_none(cx: &LateContext<'_>, expr: &Expr<'_>) {
if_chain! {
if let ExprKind::Match(subject, arms, source) = &expr.kind;
if *source == MatchSource::IfLetDesugar { contains_else_clause: true };
if Self::is_option(cx, subject);
if let PatKind::TupleStruct(path1, fields, None) = &arms[0].pat.kind;
if is_lang_ctor(cx, path1, OptionSome);
if let PatKind::Binding(annot, bind_id, _, _) = fields[0].kind;
let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
if let ExprKind::Block(block, None) = &arms[0].body.kind;
if block.stmts.is_empty();
if let Some(trailing_expr) = &block.expr;
if path_to_local_id(trailing_expr, bind_id);
if let PatKind::Wild = arms[1].pat.kind;
if Self::expression_returns_none(cx, arms[1].body);
then {
let mut applicability = Applicability::MachineApplicable;
let receiver_str = snippet_with_applicability(cx, subject.span, "..", &mut applicability);
let replacement = format!(
"{}{}?",
receiver_str,
if by_ref { ".as_ref()" } else { "" },
);
span_lint_and_sugg(
cx,
QUESTION_MARK,
expr.span,
"this if-let-else may be rewritten with the `?` operator",
"replace it with",
replacement,
applicability,
);
}
}
}
fn moves_by_default(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
let expr_ty = cx.typeck_results().expr_ty(expression);
!expr_ty.is_copy_modulo_regions(cx.tcx.at(expression.span), cx.param_env)
}
fn is_option(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
let expr_ty = cx.typeck_results().expr_ty(expression);
is_type_diagnostic_item(cx, expr_ty, sym::option_type)
}
fn expression_returns_none(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
match expression.kind {
ExprKind::Block(block, _) => {
if let Some(return_expression) = Self::return_expression(block) {
return Self::expression_returns_none(cx, return_expression);
}
false
},
ExprKind::Ret(Some(expr)) => Self::expression_returns_none(cx, expr),
ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
_ => 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(expr) = expr.kind;
if let ExprKind::Ret(Some(ret_expr)) = expr.kind;
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<'tcx> LateLintPass<'tcx> for QuestionMark {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
Self::check_is_none_and_early_return_none(cx, expr);
Self::check_if_let_some_and_early_return_none(cx, expr);
}
}
|
