rust/clippy_lints/src/manual_map.rs

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use crate::{map_unit_fn::OPTION_MAP_UNIT_FN, matches::MATCH_AS_REF};
use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::higher;
use clippy_utils::source::{snippet_with_applicability, snippet_with_context};
use clippy_utils::ty::{is_type_diagnostic_item, peel_mid_ty_refs_is_mutable};
use clippy_utils::{
can_move_expr_to_closure, in_constant, is_else_clause, is_lang_ctor, is_lint_allowed, path_to_local_id,
peel_hir_expr_refs,
};
use rustc_ast::util::parser::PREC_POSTFIX;
use rustc_errors::Applicability;
use rustc_hir::LangItem::{OptionNone, OptionSome};
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use rustc_hir::{Arm, BindingAnnotation, Block, Expr, ExprKind, HirId, Mutability, Pat, PatKind};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::{sym, SyntaxContext};
declare_clippy_lint! {
/// ### What it does
/// Checks for usages of `match` which could be implemented using `map`
///
/// ### Why is this bad?
/// Using the `map` method is clearer and more concise.
///
/// ### Example
/// ```rust
/// match Some(0) {
/// Some(x) => Some(x + 1),
/// None => None,
/// };
/// ```
/// Use instead:
/// ```rust
/// Some(0).map(|x| x + 1);
/// ```
pub MANUAL_MAP,
style,
"reimplementation of `map`"
}
declare_lint_pass!(ManualMap => [MANUAL_MAP]);
impl LateLintPass<'_> for ManualMap {
#[allow(clippy::too_many_lines)]
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if let Some(higher::IfLet {
let_pat,
let_expr,
if_then,
if_else: Some(if_else),
}) = higher::IfLet::hir(expr)
{
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manage_lint(cx, expr, (&let_pat.kind, if_then), (&PatKind::Wild, if_else), let_expr);
}
if let ExprKind::Match(scrutinee, [then @ Arm { guard: None, .. }, r#else @ Arm { guard: None, .. }], _) =
expr.kind
{
manage_lint(
cx,
expr,
(&then.pat.kind, then.body),
(&r#else.pat.kind, r#else.body),
scrutinee,
);
}
}
}
fn manage_lint<'tcx>(
cx: &LateContext<'tcx>,
expr: &'tcx Expr<'_>,
then: (&'tcx PatKind<'_>, &'tcx Expr<'_>),
r#else: (&'tcx PatKind<'_>, &'tcx Expr<'_>),
scrut: &'tcx Expr<'_>,
) {
if in_external_macro(cx.sess(), expr.span) || in_constant(cx, expr.hir_id) {
return;
}
let (scrutinee_ty, ty_ref_count, ty_mutability) = peel_mid_ty_refs_is_mutable(cx.typeck_results().expr_ty(scrut));
if !(is_type_diagnostic_item(cx, scrutinee_ty, sym::option_type)
&& is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::option_type))
{
return;
}
let (then_pat, then_expr) = then;
let (else_pat, else_expr) = r#else;
let expr_ctxt = expr.span.ctxt();
let (some_expr, some_pat, pat_ref_count, is_wild_none) = match (
try_parse_pattern(cx, then_pat, expr_ctxt),
try_parse_pattern(cx, else_pat, expr_ctxt),
) {
(Some(OptionPat::Wild), Some(OptionPat::Some { pattern, ref_count })) if is_none_expr(cx, then_expr) => {
(else_expr, pattern, ref_count, true)
},
(Some(OptionPat::None), Some(OptionPat::Some { pattern, ref_count })) if is_none_expr(cx, then_expr) => {
(else_expr, pattern, ref_count, false)
},
(Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::Wild)) if is_none_expr(cx, else_expr) => {
(then_expr, pattern, ref_count, true)
},
(Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::None)) if is_none_expr(cx, else_expr) => {
(then_expr, pattern, ref_count, false)
},
_ => return,
};
// Top level or patterns aren't allowed in closures.
if matches!(some_pat.kind, PatKind::Or(_)) {
return;
}
let some_expr = match get_some_expr(cx, some_expr, expr_ctxt) {
Some(expr) => expr,
None => return,
};
if cx.typeck_results().expr_ty(some_expr) == cx.tcx.types.unit && !is_lint_allowed(cx, OPTION_MAP_UNIT_FN, expr.hir_id) {
return;
}
// `map` won't perform any adjustments.
if !cx.typeck_results().expr_adjustments(some_expr).is_empty() {
return;
}
if !can_move_expr_to_closure(cx, some_expr) {
return;
}
// Determine which binding mode to use.
let explicit_ref = some_pat.contains_explicit_ref_binding();
let binding_ref = explicit_ref.or_else(|| (ty_ref_count != pat_ref_count).then(|| ty_mutability));
let as_ref_str = match binding_ref {
Some(Mutability::Mut) => ".as_mut()",
Some(Mutability::Not) => ".as_ref()",
None => "",
};
let mut app = Applicability::MachineApplicable;
// Remove address-of expressions from the scrutinee. Either `as_ref` will be called, or
// it's being passed by value.
let scrutinee = peel_hir_expr_refs(scrut).0;
let (scrutinee_str, _) = snippet_with_context(cx, scrutinee.span, expr_ctxt, "..", &mut app);
let scrutinee_str = if scrutinee.span.ctxt() == expr.span.ctxt() && scrutinee.precedence().order() < PREC_POSTFIX {
format!("({})", scrutinee_str)
} else {
scrutinee_str.into()
};
let body_str = if let PatKind::Binding(annotation, id, some_binding, None) = some_pat.kind {
match can_pass_as_func(cx, id, some_expr) {
Some(func) if func.span.ctxt() == some_expr.span.ctxt() => {
snippet_with_applicability(cx, func.span, "..", &mut app).into_owned()
},
_ => {
if path_to_local_id(some_expr, id)
&& !is_lint_allowed(cx, MATCH_AS_REF, expr.hir_id)
&& binding_ref.is_some()
{
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return;
}
// `ref` and `ref mut` annotations were handled earlier.
let annotation = if matches!(annotation, BindingAnnotation::Mutable) {
"mut "
} else {
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""
};
format!(
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"|{}{}| {}",
annotation,
some_binding,
snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
)
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},
}
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} else if !is_wild_none && explicit_ref.is_none() {
// TODO: handle explicit reference annotations.
format!(
"|{}| {}",
snippet_with_context(cx, some_pat.span, expr_ctxt, "..", &mut app).0,
snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
)
} else {
// Refutable bindings and mixed reference annotations can't be handled by `map`.
return;
};
span_lint_and_sugg(
cx,
MANUAL_MAP,
expr.span,
"manual implementation of `Option::map`",
"try this",
if is_else_clause(cx.tcx, expr) {
format!("{{ {}{}.map({}) }}", scrutinee_str, as_ref_str, body_str)
} else {
format!("{}{}.map({})", scrutinee_str, as_ref_str, body_str)
},
app,
);
}
// Checks whether the expression could be passed as a function, or whether a closure is needed.
// Returns the function to be passed to `map` if it exists.
fn can_pass_as_func(cx: &LateContext<'tcx>, binding: HirId, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
match expr.kind {
ExprKind::Call(func, [arg])
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if path_to_local_id (arg, binding) && cx.typeck_results().expr_adjustments(arg).is_empty() =>
{
Some(func)
},
_ => None,
}
}
enum OptionPat<'a> {
Wild,
None,
Some {
// The pattern contained in the `Some` tuple.
pattern: &'a Pat<'a>,
// The number of references before the `Some` tuple.
// e.g. `&&Some(_)` has a ref count of 2.
ref_count: usize,
},
}
// Try to parse into a recognized `Option` pattern.
// i.e. `_`, `None`, `Some(..)`, or a reference to any of those.
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fn try_parse_pattern(
cx: &LateContext<'tcx>,
pat_kind: &'tcx PatKind<'_>,
ctxt: SyntaxContext,
) -> Option<OptionPat<'tcx>> {
fn f(
cx: &LateContext<'tcx>,
pat_kind: &'tcx PatKind<'_>,
ref_count: usize,
ctxt: SyntaxContext,
) -> Option<OptionPat<'tcx>> {
match pat_kind {
PatKind::Wild => Some(OptionPat::Wild),
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PatKind::Ref(ref_pat, _) => f(cx, &ref_pat.kind, ref_count + 1, ctxt),
PatKind::Path(ref qpath) if is_lang_ctor(cx, qpath, OptionNone) => Some(OptionPat::None),
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PatKind::TupleStruct(ref qpath, [pattern], _) if is_lang_ctor(cx, qpath, OptionSome) => {
Some(OptionPat::Some { pattern, ref_count })
},
_ => None,
}
}
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f(cx, pat_kind, 0, ctxt)
}
// Checks for an expression wrapped by the `Some` constructor. Returns the contained expression.
fn get_some_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, ctxt: SyntaxContext) -> Option<&'tcx Expr<'tcx>> {
// TODO: Allow more complex expressions.
match expr.kind {
ExprKind::Call(
Expr {
kind: ExprKind::Path(ref qpath),
..
},
[arg],
) if ctxt == expr.span.ctxt() && is_lang_ctor(cx, qpath, OptionSome) => Some(arg),
ExprKind::Block(
Block {
stmts: [],
expr: Some(expr),
..
},
_,
) => get_some_expr(cx, expr, ctxt),
_ => None,
}
}
// Checks for the `None` value.
fn is_none_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
match expr.kind {
ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
ExprKind::Block(
Block {
stmts: [],
expr: Some(expr),
..
},
_,
) => is_none_expr(cx, expr),
_ => false,
}
}