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Auto merge of rust-lang#8356 - J-ZhengLi:master-issue8288, r=dswij
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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
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@bors
bors committed Jul 8, 2022
2 parents 54feac1 + d0b8f75 commit 49f73e1
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Showing 7 changed files with 312 additions and 170 deletions.
290 changes: 174 additions & 116 deletions clippy_lints/src/question_mark.rs
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Original file line number Diff line number Diff line change
@@ -1,16 +1,19 @@
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::higher;
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, is_lang_ctor, path_to_local, path_to_local_id, peel_blocks, peel_blocks_with_stmt};
use clippy_utils::{
eq_expr_value, get_parent_node, is_else_clause, is_lang_ctor, path_to_local, path_to_local_id, peel_blocks,
peel_blocks_with_stmt,
};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::LangItem::{OptionNone, OptionSome, ResultOk};
use rustc_hir::{BindingAnnotation, Expr, ExprKind, PatKind};
use rustc_hir::LangItem::{OptionNone, OptionSome, ResultErr, ResultOk};
use rustc_hir::{BindingAnnotation, Expr, ExprKind, Node, PatKind, PathSegment, QPath};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::Ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
use rustc_span::{sym, symbol::Symbol};

declare_clippy_lint! {
/// ### What it does
Expand Down Expand Up @@ -39,135 +42,190 @@ declare_clippy_lint! {

declare_lint_pass!(QuestionMark => [QUESTION_MARK]);

impl QuestionMark {
/// Checks if the given expression on the given context matches the following structure:
enum IfBlockType<'hir> {
/// An `if x.is_xxx() { a } else { b } ` expression.
///
/// ```ignore
/// if option.is_none() {
/// return None;
/// }
/// ```
///
/// ```ignore
/// if result.is_err() {
/// return result;
/// }
/// ```
/// Contains: caller (x), caller_type, call_sym (is_xxx), if_then (a), if_else (b)
IfIs(
&'hir Expr<'hir>,
Ty<'hir>,
Symbol,
&'hir Expr<'hir>,
Option<&'hir Expr<'hir>>,
),
/// An `if let Xxx(a) = b { c } else { d }` expression.
///
/// If it matches, it will suggest to use the question mark operator instead
fn check_is_none_or_err_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>) {
if_chain! {
if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr);
if let ExprKind::MethodCall(segment, args, _) = &cond.kind;
if let Some(subject) = args.get(0);
if (Self::option_check_and_early_return(cx, subject, then) && segment.ident.name == sym!(is_none)) ||
(Self::result_check_and_early_return(cx, subject, then) && segment.ident.name == sym!(is_err));
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_inner) = r#else {
if eq_expr_value(cx, subject, peel_blocks(else_inner)) {
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));
}
/// Contains: let_pat_qpath (Xxx), let_pat_type, let_pat_sym (a), let_expr (b), if_then (c),
/// if_else (d)
IfLet(
&'hir QPath<'hir>,
Ty<'hir>,
Symbol,
&'hir Expr<'hir>,
&'hir Expr<'hir>,
Option<&'hir Expr<'hir>>,
),
}

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,
);
/// Checks if the given expression on the given context matches the following structure:
///
/// ```ignore
/// if option.is_none() {
/// return None;
/// }
/// ```
///
/// ```ignore
/// if result.is_err() {
/// return result;
/// }
/// ```
///
/// If it matches, it will suggest to use the question mark operator instead
fn check_is_none_or_err_and_early_return<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
if_chain! {
if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr);
if !is_else_clause(cx.tcx, expr);
if let ExprKind::MethodCall(segment, args, _) = &cond.kind;
if let Some(caller) = args.get(0);
let caller_ty = cx.typeck_results().expr_ty(caller);
let if_block = IfBlockType::IfIs(caller, caller_ty, segment.ident.name, then, r#else);
if is_early_return(sym::Option, cx, &if_block) || is_early_return(sym::Result, cx, &if_block);
then {
let mut applicability = Applicability::MachineApplicable;
let receiver_str = snippet_with_applicability(cx, caller.span, "..", &mut applicability);
let by_ref = !caller_ty.is_copy_modulo_regions(cx.tcx.at(caller.span), cx.param_env) &&
!matches!(caller.kind, ExprKind::Call(..) | ExprKind::MethodCall(..));
let sugg = if let Some(else_inner) = r#else {
if eq_expr_value(cx, caller, peel_blocks(else_inner)) {
format!("Some({}?)", receiver_str)
} else {
return;
}
}
} else {
format!("{}{}?;", receiver_str, if by_ref { ".as_ref()" } else { "" })
};

span_lint_and_sugg(
cx,
QUESTION_MARK,
expr.span,
"this block may be rewritten with the `?` operator",
"replace it with",
sugg,
applicability,
);
}
}
}

fn check_if_let_some_or_err_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>) {
if_chain! {
if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: Some(if_else) })
= higher::IfLet::hir(cx, expr);
if let PatKind::TupleStruct(ref path1, fields, None) = let_pat.kind;
if (Self::option_check_and_early_return(cx, let_expr, if_else) && is_lang_ctor(cx, path1, OptionSome)) ||
(Self::result_check_and_early_return(cx, let_expr, if_else) && is_lang_ctor(cx, path1, ResultOk));

if let PatKind::Binding(annot, bind_id, _, _) = fields[0].kind;
fn check_if_let_some_or_err_and_early_return<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
if_chain! {
if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else }) = higher::IfLet::hir(cx, expr);
if !is_else_clause(cx.tcx, expr);
if let PatKind::TupleStruct(ref path1, fields, None) = let_pat.kind;
if let PatKind::Binding(annot, bind_id, ident, _) = fields[0].kind;
let caller_ty = cx.typeck_results().expr_ty(let_expr);
let if_block = IfBlockType::IfLet(path1, caller_ty, ident.name, let_expr, if_then, if_else);
if (is_early_return(sym::Option, cx, &if_block) && path_to_local_id(peel_blocks(if_then), bind_id))
|| is_early_return(sym::Result, cx, &if_block);
if if_else.map(|e| eq_expr_value(cx, let_expr, peel_blocks(e))).filter(|e| *e).is_none();
then {
let mut applicability = Applicability::MachineApplicable;
let receiver_str = snippet_with_applicability(cx, let_expr.span, "..", &mut applicability);
let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
if path_to_local_id(peel_blocks(if_then), bind_id);
then {
let mut applicability = Applicability::MachineApplicable;
let receiver_str = snippet_with_applicability(cx, let_expr.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,
);
}
let requires_semi = matches!(get_parent_node(cx.tcx, expr.hir_id), Some(Node::Stmt(_)));
let sugg = format!(
"{}{}?{}",
receiver_str,
if by_ref { ".as_ref()" } else { "" },
if requires_semi { ";" } else { "" }
);
span_lint_and_sugg(
cx,
QUESTION_MARK,
expr.span,
"this block may be rewritten with the `?` operator",
"replace it with",
sugg,
applicability,
);
}
}
}

fn result_check_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>, nested_expr: &Expr<'_>) -> bool {
Self::is_result(cx, expr) && Self::expression_returns_unmodified_err(nested_expr, expr)
}

fn option_check_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>, nested_expr: &Expr<'_>) -> bool {
Self::is_option(cx, expr) && Self::expression_returns_none(cx, nested_expr)
}

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)
}

fn is_result(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
let expr_ty = cx.typeck_results().expr_ty(expression);

is_type_diagnostic_item(cx, expr_ty, sym::Result)
}

fn expression_returns_none(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
match peel_blocks_with_stmt(expression).kind {
ExprKind::Ret(Some(expr)) => Self::expression_returns_none(cx, expr),
ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
_ => false,
}
fn is_early_return(smbl: Symbol, cx: &LateContext<'_>, if_block: &IfBlockType<'_>) -> bool {
match *if_block {
IfBlockType::IfIs(caller, caller_ty, call_sym, if_then, _) => {
// If the block could be identified as `if x.is_none()/is_err()`,
// we then only need to check the if_then return to see if it is none/err.
is_type_diagnostic_item(cx, caller_ty, smbl)
&& expr_return_none_or_err(smbl, cx, if_then, caller, None)
&& match smbl {
sym::Option => call_sym == sym!(is_none),
sym::Result => call_sym == sym!(is_err),
_ => false,
}
},
IfBlockType::IfLet(qpath, let_expr_ty, let_pat_sym, let_expr, if_then, if_else) => {
is_type_diagnostic_item(cx, let_expr_ty, smbl)
&& match smbl {
sym::Option => {
// We only need to check `if let Some(x) = option` not `if let None = option`,
// because the later one will be suggested as `if option.is_none()` thus causing conflict.
is_lang_ctor(cx, qpath, OptionSome)
&& if_else.is_some()
&& expr_return_none_or_err(smbl, cx, if_else.unwrap(), let_expr, None)
},
sym::Result => {
(is_lang_ctor(cx, qpath, ResultOk)
&& if_else.is_some()
&& expr_return_none_or_err(smbl, cx, if_else.unwrap(), let_expr, Some(let_pat_sym)))
|| is_lang_ctor(cx, qpath, ResultErr)
&& expr_return_none_or_err(smbl, cx, if_then, let_expr, Some(let_pat_sym))
},
_ => false,
}
},
}
}

fn expression_returns_unmodified_err(expr: &Expr<'_>, cond_expr: &Expr<'_>) -> bool {
match peel_blocks_with_stmt(expr).kind {
ExprKind::Ret(Some(ret_expr)) => Self::expression_returns_unmodified_err(ret_expr, cond_expr),
ExprKind::Path(_) => path_to_local(expr).is_some() && path_to_local(expr) == path_to_local(cond_expr),
fn expr_return_none_or_err(
smbl: Symbol,
cx: &LateContext<'_>,
expr: &Expr<'_>,
cond_expr: &Expr<'_>,
err_sym: Option<Symbol>,
) -> bool {
match peel_blocks_with_stmt(expr).kind {
ExprKind::Ret(Some(ret_expr)) => expr_return_none_or_err(smbl, cx, ret_expr, cond_expr, err_sym),
ExprKind::Path(ref qpath) => match smbl {
sym::Option => is_lang_ctor(cx, qpath, OptionNone),
sym::Result => path_to_local(expr).is_some() && path_to_local(expr) == path_to_local(cond_expr),
_ => false,
}
},
ExprKind::Call(call_expr, args_expr) => {
if_chain! {
if smbl == sym::Result;
if let ExprKind::Path(QPath::Resolved(_, path)) = &call_expr.kind;
if let Some(segment) = path.segments.first();
if let Some(err_sym) = err_sym;
if let Some(arg) = args_expr.first();
if let ExprKind::Path(QPath::Resolved(_, arg_path)) = &arg.kind;
if let Some(PathSegment { ident, .. }) = arg_path.segments.first();
then {
return segment.ident.name == sym::Err && err_sym == ident.name;
}
}
false
},
_ => false,
}
}

impl<'tcx> LateLintPass<'tcx> for QuestionMark {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
Self::check_is_none_or_err_and_early_return(cx, expr);
Self::check_if_let_some_or_err_and_early_return(cx, expr);
check_is_none_or_err_and_early_return(cx, expr);
check_if_let_some_or_err_and_early_return(cx, expr);
}
}
1 change: 1 addition & 0 deletions tests/ui/needless_match.fixed
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Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,7 @@ fn if_let_result() {
let _: Result<i32, i32> = x;
let _: Result<i32, i32> = x;
// Input type mismatch, don't trigger
#[allow(clippy::question_mark)]
let _: Result<i32, i32> = if let Err(e) = Ok(1) { Err(e) } else { x };
}

Expand Down
1 change: 1 addition & 0 deletions tests/ui/needless_match.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -122,6 +122,7 @@ fn if_let_result() {
let _: Result<i32, i32> = if let Err(e) = x { Err(e) } else { x };
let _: Result<i32, i32> = if let Ok(val) = x { Ok(val) } else { x };
// Input type mismatch, don't trigger
#[allow(clippy::question_mark)]
let _: Result<i32, i32> = if let Err(e) = Ok(1) { Err(e) } else { x };
}

Expand Down
4 changes: 2 additions & 2 deletions tests/ui/needless_match.stderr
View file
Original file line number Diff line number Diff line change
Expand Up @@ -84,7 +84,7 @@ LL | let _: Result<i32, i32> = if let Ok(val) = x { Ok(val) } else { x };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace it with: `x`

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

error: this match expression is unnecessary
--> $DIR/needless_match.rs:168:26
--> $DIR/needless_match.rs:169:26
|
LL | let _: Complex = match ce {
| __________________________^
Expand Down
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