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Auto merge of #4841 - phaylon:pattern-type-mismatch, r=flip1995
Added restriction lint: pattern-type-mismatch changelog: Added a new restriction lint `pattern-type-mismatch`. This lint is especially helpful for beginners learning about the magic behind pattern matching. (This explanation might be worth to include in the next changelog.)
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use crate::utils::{last_path_segment, span_lint_and_help}; | ||
use rustc_hir::{ | ||
intravisit, Body, Expr, ExprKind, FieldPat, FnDecl, HirId, LocalSource, MatchSource, Mutability, Pat, PatKind, | ||
QPath, Stmt, StmtKind, | ||
}; | ||
use rustc_lint::{LateContext, LateLintPass, LintContext}; | ||
use rustc_middle::lint::in_external_macro; | ||
use rustc_middle::ty::subst::SubstsRef; | ||
use rustc_middle::ty::{AdtDef, FieldDef, Ty, TyKind, VariantDef}; | ||
use rustc_session::{declare_lint_pass, declare_tool_lint}; | ||
use rustc_span::source_map::Span; | ||
|
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declare_clippy_lint! { | ||
/// **What it does:** Checks for patterns that aren't exact representations of the types | ||
/// they are applied to. | ||
/// | ||
/// To satisfy this lint, you will have to adjust either the expression that is matched | ||
/// against or the pattern itself, as well as the bindings that are introduced by the | ||
/// adjusted patterns. For matching you will have to either dereference the expression | ||
/// with the `*` operator, or amend the patterns to explicitly match against `&<pattern>` | ||
/// or `&mut <pattern>` depending on the reference mutability. For the bindings you need | ||
/// to use the inverse. You can leave them as plain bindings if you wish for the value | ||
/// to be copied, but you must use `ref mut <variable>` or `ref <variable>` to construct | ||
/// a reference into the matched structure. | ||
/// | ||
/// If you are looking for a way to learn about ownership semantics in more detail, it | ||
/// is recommended to look at IDE options available to you to highlight types, lifetimes | ||
/// and reference semantics in your code. The available tooling would expose these things | ||
/// in a general way even outside of the various pattern matching mechanics. Of course | ||
/// this lint can still be used to highlight areas of interest and ensure a good understanding | ||
/// of ownership semantics. | ||
/// | ||
/// **Why is this bad?** It isn't bad in general. But in some contexts it can be desirable | ||
/// because it increases ownership hints in the code, and will guard against some changes | ||
/// in ownership. | ||
/// | ||
/// **Known problems:** None. | ||
/// | ||
/// **Example:** | ||
/// | ||
/// This example shows the basic adjustments necessary to satisfy the lint. Note how | ||
/// the matched expression is explicitly dereferenced with `*` and the `inner` variable | ||
/// is bound to a shared borrow via `ref inner`. | ||
/// | ||
/// ```rust,ignore | ||
/// // Bad | ||
/// let value = &Some(Box::new(23)); | ||
/// match value { | ||
/// Some(inner) => println!("{}", inner), | ||
/// None => println!("none"), | ||
/// } | ||
/// | ||
/// // Good | ||
/// let value = &Some(Box::new(23)); | ||
/// match *value { | ||
/// Some(ref inner) => println!("{}", inner), | ||
/// None => println!("none"), | ||
/// } | ||
/// ``` | ||
/// | ||
/// The following example demonstrates one of the advantages of the more verbose style. | ||
/// Note how the second version uses `ref mut a` to explicitly declare `a` a shared mutable | ||
/// borrow, while `b` is simply taken by value. This ensures that the loop body cannot | ||
/// accidentally modify the wrong part of the structure. | ||
/// | ||
/// ```rust,ignore | ||
/// // Bad | ||
/// let mut values = vec![(2, 3), (3, 4)]; | ||
/// for (a, b) in &mut values { | ||
/// *a += *b; | ||
/// } | ||
/// | ||
/// // Good | ||
/// let mut values = vec![(2, 3), (3, 4)]; | ||
/// for &mut (ref mut a, b) in &mut values { | ||
/// *a += b; | ||
/// } | ||
/// ``` | ||
pub PATTERN_TYPE_MISMATCH, | ||
restriction, | ||
"type of pattern does not match the expression type" | ||
} | ||
|
||
declare_lint_pass!(PatternTypeMismatch => [PATTERN_TYPE_MISMATCH]); | ||
|
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impl<'tcx> LateLintPass<'tcx> for PatternTypeMismatch { | ||
fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) { | ||
if let StmtKind::Local(ref local) = stmt.kind { | ||
if let Some(init) = &local.init { | ||
if let Some(init_ty) = cx.tables().node_type_opt(init.hir_id) { | ||
let pat = &local.pat; | ||
if in_external_macro(cx.sess(), pat.span) { | ||
return; | ||
} | ||
let deref_possible = match local.source { | ||
LocalSource::Normal => DerefPossible::Possible, | ||
_ => DerefPossible::Impossible, | ||
}; | ||
apply_lint(cx, pat, init_ty, deref_possible); | ||
} | ||
} | ||
} | ||
} | ||
|
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { | ||
if let ExprKind::Match(ref expr, arms, source) = expr.kind { | ||
match source { | ||
MatchSource::Normal | MatchSource::IfLetDesugar { .. } | MatchSource::WhileLetDesugar => { | ||
if let Some(expr_ty) = cx.tables().node_type_opt(expr.hir_id) { | ||
'pattern_checks: for arm in arms { | ||
let pat = &arm.pat; | ||
if in_external_macro(cx.sess(), pat.span) { | ||
continue 'pattern_checks; | ||
} | ||
if apply_lint(cx, pat, expr_ty, DerefPossible::Possible) { | ||
break 'pattern_checks; | ||
} | ||
} | ||
} | ||
}, | ||
_ => (), | ||
} | ||
} | ||
} | ||
|
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fn check_fn( | ||
&mut self, | ||
cx: &LateContext<'tcx>, | ||
_: intravisit::FnKind<'tcx>, | ||
_: &'tcx FnDecl<'_>, | ||
body: &'tcx Body<'_>, | ||
_: Span, | ||
hir_id: HirId, | ||
) { | ||
if let Some(fn_sig) = cx.tables().liberated_fn_sigs().get(hir_id) { | ||
for (param, ty) in body.params.iter().zip(fn_sig.inputs().iter()) { | ||
apply_lint(cx, ¶m.pat, ty, DerefPossible::Impossible); | ||
} | ||
} | ||
} | ||
} | ||
|
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#[derive(Debug, Clone, Copy)] | ||
enum DerefPossible { | ||
Possible, | ||
Impossible, | ||
} | ||
|
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fn apply_lint<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'_>, expr_ty: Ty<'tcx>, deref_possible: DerefPossible) -> bool { | ||
let maybe_mismatch = find_first_mismatch(cx, pat, expr_ty, Level::Top); | ||
if let Some((span, mutability, level)) = maybe_mismatch { | ||
span_lint_and_help( | ||
cx, | ||
PATTERN_TYPE_MISMATCH, | ||
span, | ||
"type of pattern does not match the expression type", | ||
None, | ||
&format!( | ||
"{}explicitly match against a `{}` pattern and adjust the enclosed variable bindings", | ||
match (deref_possible, level) { | ||
(DerefPossible::Possible, Level::Top) => "use `*` to dereference the match expression or ", | ||
_ => "", | ||
}, | ||
match mutability { | ||
Mutability::Mut => "&mut _", | ||
Mutability::Not => "&_", | ||
}, | ||
), | ||
); | ||
true | ||
} else { | ||
false | ||
} | ||
} | ||
|
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#[derive(Debug, Copy, Clone)] | ||
enum Level { | ||
Top, | ||
Lower, | ||
} | ||
|
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#[allow(rustc::usage_of_ty_tykind)] | ||
fn find_first_mismatch<'tcx>( | ||
cx: &LateContext<'tcx>, | ||
pat: &Pat<'_>, | ||
ty: Ty<'tcx>, | ||
level: Level, | ||
) -> Option<(Span, Mutability, Level)> { | ||
if let PatKind::Ref(ref sub_pat, _) = pat.kind { | ||
if let TyKind::Ref(_, sub_ty, _) = ty.kind { | ||
return find_first_mismatch(cx, sub_pat, sub_ty, Level::Lower); | ||
} | ||
} | ||
|
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if let TyKind::Ref(_, _, mutability) = ty.kind { | ||
if is_non_ref_pattern(&pat.kind) { | ||
return Some((pat.span, mutability, level)); | ||
} | ||
} | ||
|
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if let PatKind::Struct(ref qpath, ref field_pats, _) = pat.kind { | ||
if let TyKind::Adt(ref adt_def, ref substs_ref) = ty.kind { | ||
if let Some(variant) = get_variant(adt_def, qpath) { | ||
let field_defs = &variant.fields; | ||
return find_first_mismatch_in_struct(cx, field_pats, field_defs, substs_ref); | ||
} | ||
} | ||
} | ||
|
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if let PatKind::TupleStruct(ref qpath, ref pats, _) = pat.kind { | ||
if let TyKind::Adt(ref adt_def, ref substs_ref) = ty.kind { | ||
if let Some(variant) = get_variant(adt_def, qpath) { | ||
let field_defs = &variant.fields; | ||
let ty_iter = field_defs.iter().map(|field_def| field_def.ty(cx.tcx, substs_ref)); | ||
return find_first_mismatch_in_tuple(cx, pats, ty_iter); | ||
} | ||
} | ||
} | ||
|
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if let PatKind::Tuple(ref pats, _) = pat.kind { | ||
if let TyKind::Tuple(..) = ty.kind { | ||
return find_first_mismatch_in_tuple(cx, pats, ty.tuple_fields()); | ||
} | ||
} | ||
|
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if let PatKind::Or(sub_pats) = pat.kind { | ||
for pat in sub_pats { | ||
let maybe_mismatch = find_first_mismatch(cx, pat, ty, level); | ||
if let Some(mismatch) = maybe_mismatch { | ||
return Some(mismatch); | ||
} | ||
} | ||
} | ||
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None | ||
} | ||
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fn get_variant<'a>(adt_def: &'a AdtDef, qpath: &QPath<'_>) -> Option<&'a VariantDef> { | ||
if adt_def.is_struct() { | ||
if let Some(variant) = adt_def.variants.iter().next() { | ||
return Some(variant); | ||
} | ||
} | ||
|
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if adt_def.is_enum() { | ||
let pat_ident = last_path_segment(qpath).ident; | ||
for variant in &adt_def.variants { | ||
if variant.ident == pat_ident { | ||
return Some(variant); | ||
} | ||
} | ||
} | ||
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None | ||
} | ||
|
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fn find_first_mismatch_in_tuple<'tcx, I>( | ||
cx: &LateContext<'tcx>, | ||
pats: &[&Pat<'_>], | ||
ty_iter_src: I, | ||
) -> Option<(Span, Mutability, Level)> | ||
where | ||
I: IntoIterator<Item = Ty<'tcx>>, | ||
{ | ||
let mut field_tys = ty_iter_src.into_iter(); | ||
'fields: for pat in pats { | ||
let field_ty = if let Some(ty) = field_tys.next() { | ||
ty | ||
} else { | ||
break 'fields; | ||
}; | ||
|
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let maybe_mismatch = find_first_mismatch(cx, pat, field_ty, Level::Lower); | ||
if let Some(mismatch) = maybe_mismatch { | ||
return Some(mismatch); | ||
} | ||
} | ||
|
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None | ||
} | ||
|
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fn find_first_mismatch_in_struct<'tcx>( | ||
cx: &LateContext<'tcx>, | ||
field_pats: &[FieldPat<'_>], | ||
field_defs: &[FieldDef], | ||
substs_ref: SubstsRef<'tcx>, | ||
) -> Option<(Span, Mutability, Level)> { | ||
for field_pat in field_pats { | ||
'definitions: for field_def in field_defs { | ||
if field_pat.ident == field_def.ident { | ||
let field_ty = field_def.ty(cx.tcx, substs_ref); | ||
let pat = &field_pat.pat; | ||
let maybe_mismatch = find_first_mismatch(cx, pat, field_ty, Level::Lower); | ||
if let Some(mismatch) = maybe_mismatch { | ||
return Some(mismatch); | ||
} | ||
break 'definitions; | ||
} | ||
} | ||
} | ||
|
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None | ||
} | ||
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fn is_non_ref_pattern(pat_kind: &PatKind<'_>) -> bool { | ||
match pat_kind { | ||
PatKind::Struct(..) | PatKind::Tuple(..) | PatKind::TupleStruct(..) | PatKind::Path(..) => true, | ||
PatKind::Or(sub_pats) => sub_pats.iter().any(|pat| is_non_ref_pattern(&pat.kind)), | ||
_ => false, | ||
} | ||
} |
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