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Simplify if let statements
fixes: rust-lang#8288 --- changelog: Allowing [`qustion_mark`] lint to check `if let` expressions that immediatly return unwrapped value
1 parent 4198013 commit d0b8f75

7 files changed

+312
-170
lines changed

‎clippy_lints/src/question_mark.rs

+174-116
Original file line numberDiff line numberDiff line change
@@ -1,16 +1,19 @@
11
use clippy_utils::diagnostics::span_lint_and_sugg;
22
use clippy_utils::higher;
33
use clippy_utils::source::snippet_with_applicability;
4-
use clippy_utils::sugg::Sugg;
54
use clippy_utils::ty::is_type_diagnostic_item;
6-
use clippy_utils::{eq_expr_value, is_lang_ctor, path_to_local, path_to_local_id, peel_blocks, peel_blocks_with_stmt};
5+
use clippy_utils::{
6+
eq_expr_value, get_parent_node, is_else_clause, is_lang_ctor, path_to_local, path_to_local_id, peel_blocks,
7+
peel_blocks_with_stmt,
8+
};
79
use if_chain::if_chain;
810
use rustc_errors::Applicability;
9-
use rustc_hir::LangItem::{OptionNone, OptionSome, ResultOk};
10-
use rustc_hir::{BindingAnnotation, Expr, ExprKind, PatKind};
11+
use rustc_hir::LangItem::{OptionNone, OptionSome, ResultErr, ResultOk};
12+
use rustc_hir::{BindingAnnotation, Expr, ExprKind, Node, PatKind, PathSegment, QPath};
1113
use rustc_lint::{LateContext, LateLintPass};
14+
use rustc_middle::ty::Ty;
1215
use rustc_session::{declare_lint_pass, declare_tool_lint};
13-
use rustc_span::sym;
16+
use rustc_span::{sym, symbol::Symbol};
1417

1518
declare_clippy_lint! {
1619
/// ### What it does
@@ -39,135 +42,190 @@ declare_clippy_lint! {
3942

4043
declare_lint_pass!(QuestionMark => [QUESTION_MARK]);
4144

42-
impl QuestionMark {
43-
/// Checks if the given expression on the given context matches the following structure:
45+
enum IfBlockType<'hir> {
46+
/// An `if x.is_xxx() { a } else { b } ` expression.
4447
///
45-
/// ```ignore
46-
/// if option.is_none() {
47-
/// return None;
48-
/// }
49-
/// ```
50-
///
51-
/// ```ignore
52-
/// if result.is_err() {
53-
/// return result;
54-
/// }
55-
/// ```
48+
/// Contains: caller (x), caller_type, call_sym (is_xxx), if_then (a), if_else (b)
49+
IfIs(
50+
&'hir Expr<'hir>,
51+
Ty<'hir>,
52+
Symbol,
53+
&'hir Expr<'hir>,
54+
Option<&'hir Expr<'hir>>,
55+
),
56+
/// An `if let Xxx(a) = b { c } else { d }` expression.
5657
///
57-
/// If it matches, it will suggest to use the question mark operator instead
58-
fn check_is_none_or_err_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>) {
59-
if_chain! {
60-
if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr);
61-
if let ExprKind::MethodCall(segment, args, _) = &cond.kind;
62-
if let Some(subject) = args.get(0);
63-
if (Self::option_check_and_early_return(cx, subject, then) && segment.ident.name == sym!(is_none)) ||
64-
(Self::result_check_and_early_return(cx, subject, then) && segment.ident.name == sym!(is_err));
65-
then {
66-
let mut applicability = Applicability::MachineApplicable;
67-
let receiver_str = &Sugg::hir_with_applicability(cx, subject, "..", &mut applicability);
68-
let mut replacement: Option<String> = None;
69-
if let Some(else_inner) = r#else {
70-
if eq_expr_value(cx, subject, peel_blocks(else_inner)) {
71-
replacement = Some(format!("Some({}?)", receiver_str));
72-
}
73-
} else if Self::moves_by_default(cx, subject)
74-
&& !matches!(subject.kind, ExprKind::Call(..) | ExprKind::MethodCall(..))
75-
{
76-
replacement = Some(format!("{}.as_ref()?;", receiver_str));
77-
} else {
78-
replacement = Some(format!("{}?;", receiver_str));
79-
}
58+
/// Contains: let_pat_qpath (Xxx), let_pat_type, let_pat_sym (a), let_expr (b), if_then (c),
59+
/// if_else (d)
60+
IfLet(
61+
&'hir QPath<'hir>,
62+
Ty<'hir>,
63+
Symbol,
64+
&'hir Expr<'hir>,
65+
&'hir Expr<'hir>,
66+
Option<&'hir Expr<'hir>>,
67+
),
68+
}
8069

81-
if let Some(replacement_str) = replacement {
82-
span_lint_and_sugg(
83-
cx,
84-
QUESTION_MARK,
85-
expr.span,
86-
"this block may be rewritten with the `?` operator",
87-
"replace it with",
88-
replacement_str,
89-
applicability,
90-
);
70+
/// Checks if the given expression on the given context matches the following structure:
71+
///
72+
/// ```ignore
73+
/// if option.is_none() {
74+
/// return None;
75+
/// }
76+
/// ```
77+
///
78+
/// ```ignore
79+
/// if result.is_err() {
80+
/// return result;
81+
/// }
82+
/// ```
83+
///
84+
/// If it matches, it will suggest to use the question mark operator instead
85+
fn check_is_none_or_err_and_early_return<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
86+
if_chain! {
87+
if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr);
88+
if !is_else_clause(cx.tcx, expr);
89+
if let ExprKind::MethodCall(segment, args, _) = &cond.kind;
90+
if let Some(caller) = args.get(0);
91+
let caller_ty = cx.typeck_results().expr_ty(caller);
92+
let if_block = IfBlockType::IfIs(caller, caller_ty, segment.ident.name, then, r#else);
93+
if is_early_return(sym::Option, cx, &if_block) || is_early_return(sym::Result, cx, &if_block);
94+
then {
95+
let mut applicability = Applicability::MachineApplicable;
96+
let receiver_str = snippet_with_applicability(cx, caller.span, "..", &mut applicability);
97+
let by_ref = !caller_ty.is_copy_modulo_regions(cx.tcx.at(caller.span), cx.param_env) &&
98+
!matches!(caller.kind, ExprKind::Call(..) | ExprKind::MethodCall(..));
99+
let sugg = if let Some(else_inner) = r#else {
100+
if eq_expr_value(cx, caller, peel_blocks(else_inner)) {
101+
format!("Some({}?)", receiver_str)
102+
} else {
103+
return;
91104
}
92-
}
105+
} else {
106+
format!("{}{}?;", receiver_str, if by_ref { ".as_ref()" } else { "" })
107+
};
108+
109+
span_lint_and_sugg(
110+
cx,
111+
QUESTION_MARK,
112+
expr.span,
113+
"this block may be rewritten with the `?` operator",
114+
"replace it with",
115+
sugg,
116+
applicability,
117+
);
93118
}
94119
}
120+
}
95121

96-
fn check_if_let_some_or_err_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>) {
97-
if_chain! {
98-
if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: Some(if_else) })
99-
= higher::IfLet::hir(cx, expr);
100-
if let PatKind::TupleStruct(ref path1, fields, None) = let_pat.kind;
101-
if (Self::option_check_and_early_return(cx, let_expr, if_else) && is_lang_ctor(cx, path1, OptionSome)) ||
102-
(Self::result_check_and_early_return(cx, let_expr, if_else) && is_lang_ctor(cx, path1, ResultOk));
103-
104-
if let PatKind::Binding(annot, bind_id, _, _) = fields[0].kind;
122+
fn check_if_let_some_or_err_and_early_return<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
123+
if_chain! {
124+
if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else }) = higher::IfLet::hir(cx, expr);
125+
if !is_else_clause(cx.tcx, expr);
126+
if let PatKind::TupleStruct(ref path1, fields, None) = let_pat.kind;
127+
if let PatKind::Binding(annot, bind_id, ident, _) = fields[0].kind;
128+
let caller_ty = cx.typeck_results().expr_ty(let_expr);
129+
let if_block = IfBlockType::IfLet(path1, caller_ty, ident.name, let_expr, if_then, if_else);
130+
if (is_early_return(sym::Option, cx, &if_block) && path_to_local_id(peel_blocks(if_then), bind_id))
131+
|| is_early_return(sym::Result, cx, &if_block);
132+
if if_else.map(|e| eq_expr_value(cx, let_expr, peel_blocks(e))).filter(|e| *e).is_none();
133+
then {
134+
let mut applicability = Applicability::MachineApplicable;
135+
let receiver_str = snippet_with_applicability(cx, let_expr.span, "..", &mut applicability);
105136
let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
106-
if path_to_local_id(peel_blocks(if_then), bind_id);
107-
then {
108-
let mut applicability = Applicability::MachineApplicable;
109-
let receiver_str = snippet_with_applicability(cx, let_expr.span, "..", &mut applicability);
110-
let replacement = format!("{}{}?", receiver_str, if by_ref { ".as_ref()" } else { "" },);
111-
112-
span_lint_and_sugg(
113-
cx,
114-
QUESTION_MARK,
115-
expr.span,
116-
"this if-let-else may be rewritten with the `?` operator",
117-
"replace it with",
118-
replacement,
119-
applicability,
120-
);
121-
}
137+
let requires_semi = matches!(get_parent_node(cx.tcx, expr.hir_id), Some(Node::Stmt(_)));
138+
let sugg = format!(
139+
"{}{}?{}",
140+
receiver_str,
141+
if by_ref { ".as_ref()" } else { "" },
142+
if requires_semi { ";" } else { "" }
143+
);
144+
span_lint_and_sugg(
145+
cx,
146+
QUESTION_MARK,
147+
expr.span,
148+
"this block may be rewritten with the `?` operator",
149+
"replace it with",
150+
sugg,
151+
applicability,
152+
);
122153
}
123154
}
155+
}
124156

125-
fn result_check_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>, nested_expr: &Expr<'_>) -> bool {
126-
Self::is_result(cx, expr) && Self::expression_returns_unmodified_err(nested_expr, expr)
127-
}
128-
129-
fn option_check_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>, nested_expr: &Expr<'_>) -> bool {
130-
Self::is_option(cx, expr) && Self::expression_returns_none(cx, nested_expr)
131-
}
132-
133-
fn moves_by_default(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
134-
let expr_ty = cx.typeck_results().expr_ty(expression);
135-
136-
!expr_ty.is_copy_modulo_regions(cx.tcx.at(expression.span), cx.param_env)
137-
}
138-
139-
fn is_option(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
140-
let expr_ty = cx.typeck_results().expr_ty(expression);
141-
142-
is_type_diagnostic_item(cx, expr_ty, sym::Option)
143-
}
144-
145-
fn is_result(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
146-
let expr_ty = cx.typeck_results().expr_ty(expression);
147-
148-
is_type_diagnostic_item(cx, expr_ty, sym::Result)
149-
}
150-
151-
fn expression_returns_none(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
152-
match peel_blocks_with_stmt(expression).kind {
153-
ExprKind::Ret(Some(expr)) => Self::expression_returns_none(cx, expr),
154-
ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
155-
_ => false,
156-
}
157+
fn is_early_return(smbl: Symbol, cx: &LateContext<'_>, if_block: &IfBlockType<'_>) -> bool {
158+
match *if_block {
159+
IfBlockType::IfIs(caller, caller_ty, call_sym, if_then, _) => {
160+
// If the block could be identified as `if x.is_none()/is_err()`,
161+
// we then only need to check the if_then return to see if it is none/err.
162+
is_type_diagnostic_item(cx, caller_ty, smbl)
163+
&& expr_return_none_or_err(smbl, cx, if_then, caller, None)
164+
&& match smbl {
165+
sym::Option => call_sym == sym!(is_none),
166+
sym::Result => call_sym == sym!(is_err),
167+
_ => false,
168+
}
169+
},
170+
IfBlockType::IfLet(qpath, let_expr_ty, let_pat_sym, let_expr, if_then, if_else) => {
171+
is_type_diagnostic_item(cx, let_expr_ty, smbl)
172+
&& match smbl {
173+
sym::Option => {
174+
// We only need to check `if let Some(x) = option` not `if let None = option`,
175+
// because the later one will be suggested as `if option.is_none()` thus causing conflict.
176+
is_lang_ctor(cx, qpath, OptionSome)
177+
&& if_else.is_some()
178+
&& expr_return_none_or_err(smbl, cx, if_else.unwrap(), let_expr, None)
179+
},
180+
sym::Result => {
181+
(is_lang_ctor(cx, qpath, ResultOk)
182+
&& if_else.is_some()
183+
&& expr_return_none_or_err(smbl, cx, if_else.unwrap(), let_expr, Some(let_pat_sym)))
184+
|| is_lang_ctor(cx, qpath, ResultErr)
185+
&& expr_return_none_or_err(smbl, cx, if_then, let_expr, Some(let_pat_sym))
186+
},
187+
_ => false,
188+
}
189+
},
157190
}
191+
}
158192

159-
fn expression_returns_unmodified_err(expr: &Expr<'_>, cond_expr: &Expr<'_>) -> bool {
160-
match peel_blocks_with_stmt(expr).kind {
161-
ExprKind::Ret(Some(ret_expr)) => Self::expression_returns_unmodified_err(ret_expr, cond_expr),
162-
ExprKind::Path(_) => path_to_local(expr).is_some() && path_to_local(expr) == path_to_local(cond_expr),
193+
fn expr_return_none_or_err(
194+
smbl: Symbol,
195+
cx: &LateContext<'_>,
196+
expr: &Expr<'_>,
197+
cond_expr: &Expr<'_>,
198+
err_sym: Option<Symbol>,
199+
) -> bool {
200+
match peel_blocks_with_stmt(expr).kind {
201+
ExprKind::Ret(Some(ret_expr)) => expr_return_none_or_err(smbl, cx, ret_expr, cond_expr, err_sym),
202+
ExprKind::Path(ref qpath) => match smbl {
203+
sym::Option => is_lang_ctor(cx, qpath, OptionNone),
204+
sym::Result => path_to_local(expr).is_some() && path_to_local(expr) == path_to_local(cond_expr),
163205
_ => false,
164-
}
206+
},
207+
ExprKind::Call(call_expr, args_expr) => {
208+
if_chain! {
209+
if smbl == sym::Result;
210+
if let ExprKind::Path(QPath::Resolved(_, path)) = &call_expr.kind;
211+
if let Some(segment) = path.segments.first();
212+
if let Some(err_sym) = err_sym;
213+
if let Some(arg) = args_expr.first();
214+
if let ExprKind::Path(QPath::Resolved(_, arg_path)) = &arg.kind;
215+
if let Some(PathSegment { ident, .. }) = arg_path.segments.first();
216+
then {
217+
return segment.ident.name == sym::Err && err_sym == ident.name;
218+
}
219+
}
220+
false
221+
},
222+
_ => false,
165223
}
166224
}
167225

168226
impl<'tcx> LateLintPass<'tcx> for QuestionMark {
169227
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
170-
Self::check_is_none_or_err_and_early_return(cx, expr);
171-
Self::check_if_let_some_or_err_and_early_return(cx, expr);
228+
check_is_none_or_err_and_early_return(cx, expr);
229+
check_if_let_some_or_err_and_early_return(cx, expr);
172230
}
173231
}

‎tests/ui/needless_match.fixed

+1
Original file line numberDiff line numberDiff line change
@@ -99,6 +99,7 @@ fn if_let_result() {
9999
let _: Result<i32, i32> = x;
100100
let _: Result<i32, i32> = x;
101101
// Input type mismatch, don't trigger
102+
#[allow(clippy::question_mark)]
102103
let _: Result<i32, i32> = if let Err(e) = Ok(1) { Err(e) } else { x };
103104
}
104105

‎tests/ui/needless_match.rs

+1
Original file line numberDiff line numberDiff line change
@@ -122,6 +122,7 @@ fn if_let_result() {
122122
let _: Result<i32, i32> = if let Err(e) = x { Err(e) } else { x };
123123
let _: Result<i32, i32> = if let Ok(val) = x { Ok(val) } else { x };
124124
// Input type mismatch, don't trigger
125+
#[allow(clippy::question_mark)]
125126
let _: Result<i32, i32> = if let Err(e) = Ok(1) { Err(e) } else { x };
126127
}
127128

‎tests/ui/needless_match.stderr

+2-2
Original file line numberDiff line numberDiff line change
@@ -84,7 +84,7 @@ LL | let _: Result<i32, i32> = if let Ok(val) = x { Ok(val) } else { x };
8484
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace it with: `x`
8585

8686
error: this if-let expression is unnecessary
87-
--> $DIR/needless_match.rs:129:21
87+
--> $DIR/needless_match.rs:130:21
8888
|
8989
LL | let _: Simple = if let Simple::A = x {
9090
| _____________________^
@@ -97,7 +97,7 @@ LL | | };
9797
| |_____^ help: replace it with: `x`
9898

9999
error: this match expression is unnecessary
100-
--> $DIR/needless_match.rs:168:26
100+
--> $DIR/needless_match.rs:169:26
101101
|
102102
LL | let _: Complex = match ce {
103103
| __________________________^

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