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Merged
merged 5 commits into from
Jan 14, 2019
Merged

Point at match discriminant on type error in match arm pattern #57366

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a873337
Point at the match discriminant when arm pattern has a type mismatch
estebank Jan 6, 2019
f9e10f1
tidy fix
estebank Jan 6, 2019
72d965f
Reword label as per review comment
estebank Jan 6, 2019
486ecc5
Don't add label to the match expr when the type is not fully realized
estebank Jan 6, 2019
10fbdbf
Update documentation comment
estebank Jan 9, 2019
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5 changes: 5 additions & 0 deletions src/librustc/infer/error_reporting/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -487,6 +487,11 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {

fn note_error_origin(&self, err: &mut DiagnosticBuilder<'tcx>, cause: &ObligationCause<'tcx>) {
match cause.code {
ObligationCauseCode::MatchExpressionArmPattern { span, ty } => {
if ty.is_suggestable() { // don't show type `_`
err.span_label(span, format!("this match expression has type `{}`", ty));
}
}
ObligationCauseCode::MatchExpressionArm { arm_span, source } => match source {
hir::MatchSource::IfLetDesugar { .. } => {
let msg = "`if let` arm with an incompatible type";
Expand Down
4 changes: 2 additions & 2 deletions src/librustc/traits/error_reporting.rs
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Expand Up @@ -1444,15 +1444,15 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
match *cause_code {
ObligationCauseCode::ExprAssignable |
ObligationCauseCode::MatchExpressionArm { .. } |
ObligationCauseCode::MatchExpressionArmPattern { .. } |
ObligationCauseCode::IfExpression |
ObligationCauseCode::IfExpressionWithNoElse |
ObligationCauseCode::MainFunctionType |
ObligationCauseCode::StartFunctionType |
ObligationCauseCode::IntrinsicType |
ObligationCauseCode::MethodReceiver |
ObligationCauseCode::ReturnNoExpression |
ObligationCauseCode::MiscObligation => {
}
ObligationCauseCode::MiscObligation => {}
ObligationCauseCode::SliceOrArrayElem => {
err.note("slice and array elements must have `Sized` type");
}
Expand Down
9 changes: 7 additions & 2 deletions src/librustc/traits/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -220,8 +220,13 @@ pub enum ObligationCauseCode<'tcx> {
ExprAssignable,

/// Computing common supertype in the arms of a match expression
MatchExpressionArm { arm_span: Span,
source: hir::MatchSource },
MatchExpressionArm {
arm_span: Span,
source: hir::MatchSource,
},

/// Computing common supertype in the pattern guard for the arms of a match expression
MatchExpressionArmPattern { span: Span, ty: Ty<'tcx> },

/// Computing common supertype in an if expression
IfExpression,
Expand Down
3 changes: 3 additions & 0 deletions src/librustc/traits/structural_impls.rs
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Expand Up @@ -517,6 +517,9 @@ impl<'a, 'tcx> Lift<'tcx> for traits::ObligationCauseCode<'a> {
arm_span,
source: source,
}),
super::MatchExpressionArmPattern { span, ty } => {
tcx.lift(&ty).map(|ty| super::MatchExpressionArmPattern { span, ty })
}
super::IfExpression => Some(super::IfExpression),
super::IfExpressionWithNoElse => Some(super::IfExpressionWithNoElse),
super::MainFunctionType => Some(super::MainFunctionType),
Expand Down
173 changes: 104 additions & 69 deletions src/librustc_typeck/check/_match.rs
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Expand Up @@ -20,21 +20,33 @@ use std::cmp;
use super::report_unexpected_variant_def;

impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
/// The `is_arg` argument indicates whether this pattern is the
/// *outermost* pattern in an argument (e.g., in `fn foo(&x:
/// &u32)`, it is true for the `&x` pattern but not `x`). This is
/// used to tailor error reporting.
/// `match_discrim_span` argument having a `Span` indicates that this pattern is part of
/// a match expression arm guard, and it points to the match discriminant to add context
/// in type errors. In the folloowing example, `match_discrim_span` corresponds to the
/// `a + b` expression:
///
/// ```text
/// error[E0308]: mismatched types
/// --> src/main.rs:5:9
/// |
/// 4 | let temp: usize = match a + b {
/// | ----- this expression has type `usize`
/// 5 | Ok(num) => num,
/// | ^^^^^^^ expected usize, found enum `std::result::Result`
/// |
/// = note: expected type `usize`
/// found type `std::result::Result<_, _>`
/// ```
pub fn check_pat_walk(
&self,
pat: &'gcx hir::Pat,
mut expected: Ty<'tcx>,
mut def_bm: ty::BindingMode,
is_arg: bool)
{
match_discrim_span: Option<Span>,
) {
let tcx = self.tcx;

debug!("check_pat_walk(pat={:?},expected={:?},def_bm={:?},is_arg={})",
pat, expected, def_bm, is_arg);
debug!("check_pat_walk(pat={:?},expected={:?},def_bm={:?})", pat, expected, def_bm);

let is_non_ref_pat = match pat.node {
PatKind::Struct(..) |
Expand Down Expand Up @@ -210,8 +222,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
let common_type = self.resolve_type_vars_if_possible(&lhs_ty);

// subtyping doesn't matter here, as the value is some kind of scalar
self.demand_eqtype(pat.span, expected, lhs_ty);
self.demand_eqtype(pat.span, expected, rhs_ty);
self.demand_eqtype_pat(pat.span, expected, lhs_ty, match_discrim_span);
self.demand_eqtype_pat(pat.span, expected, rhs_ty, match_discrim_span);
common_type
}
PatKind::Binding(ba, var_id, _, ref sub) => {
Expand Down Expand Up @@ -240,37 +252,45 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
// `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)` is
// required. However, we use equality, which is stronger. See (*) for
// an explanation.
self.demand_eqtype(pat.span, region_ty, local_ty);
self.demand_eqtype_pat(pat.span, region_ty, local_ty, match_discrim_span);
}
// otherwise the type of x is the expected type T
ty::BindByValue(_) => {
// As above, `T <: typeof(x)` is required but we
// use equality, see (*) below.
self.demand_eqtype(pat.span, expected, local_ty);
self.demand_eqtype_pat(pat.span, expected, local_ty, match_discrim_span);
}
}

// if there are multiple arms, make sure they all agree on
// what the type of the binding `x` ought to be
if var_id != pat.id {
let vt = self.local_ty(pat.span, var_id).decl_ty;
self.demand_eqtype(pat.span, vt, local_ty);
self.demand_eqtype_pat(pat.span, vt, local_ty, match_discrim_span);
}

if let Some(ref p) = *sub {
self.check_pat_walk(&p, expected, def_bm, true);
self.check_pat_walk(&p, expected, def_bm, match_discrim_span);
}

local_ty
}
PatKind::TupleStruct(ref qpath, ref subpats, ddpos) => {
self.check_pat_tuple_struct(pat, qpath, &subpats, ddpos, expected, def_bm)
self.check_pat_tuple_struct(
pat,
qpath,
&subpats,
ddpos,
expected,
def_bm,
match_discrim_span,
)
}
PatKind::Path(ref qpath) => {
self.check_pat_path(pat, qpath, expected)
}
PatKind::Struct(ref qpath, ref fields, etc) => {
self.check_pat_struct(pat, qpath, fields, etc, expected, def_bm)
self.check_pat_struct(pat, qpath, fields, etc, expected, def_bm, match_discrim_span)
}
PatKind::Tuple(ref elements, ddpos) => {
let mut expected_len = elements.len();
Expand All @@ -295,12 +315,12 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
// further errors being emitted when using the bindings. #50333
let element_tys_iter = (0..max_len).map(|_| tcx.types.err);
for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
self.check_pat_walk(elem, &tcx.types.err, def_bm, true);
self.check_pat_walk(elem, &tcx.types.err, def_bm, match_discrim_span);
}
tcx.mk_tup(element_tys_iter)
} else {
for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
self.check_pat_walk(elem, &element_tys[i], def_bm, true);
self.check_pat_walk(elem, &element_tys[i], def_bm, match_discrim_span);
}
pat_ty
}
Expand All @@ -313,11 +333,11 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
// Here, `demand::subtype` is good enough, but I don't
// think any errors can be introduced by using
// `demand::eqtype`.
self.demand_eqtype(pat.span, expected, uniq_ty);
self.check_pat_walk(&inner, inner_ty, def_bm, true);
self.demand_eqtype_pat(pat.span, expected, uniq_ty, match_discrim_span);
self.check_pat_walk(&inner, inner_ty, def_bm, match_discrim_span);
uniq_ty
} else {
self.check_pat_walk(&inner, tcx.types.err, def_bm, true);
self.check_pat_walk(&inner, tcx.types.err, def_bm, match_discrim_span);
tcx.types.err
}
}
Expand Down Expand Up @@ -349,15 +369,13 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
// Look for a case like `fn foo(&foo: u32)` and suggest
// `fn foo(foo: &u32)`
if let Some(mut err) = err {
if is_arg {
if let PatKind::Binding(..) = inner.node {
if let Ok(snippet) = tcx.sess.source_map()
.span_to_snippet(pat.span)
{
err.help(&format!("did you mean `{}: &{}`?",
&snippet[1..],
expected));
}
if let PatKind::Binding(..) = inner.node {
if let Ok(snippet) = tcx.sess.source_map()
.span_to_snippet(pat.span)
{
err.help(&format!("did you mean `{}: &{}`?",
&snippet[1..],
expected));
}
}
err.emit();
Expand All @@ -366,10 +384,10 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
}
};

self.check_pat_walk(&inner, inner_ty, def_bm, true);
self.check_pat_walk(&inner, inner_ty, def_bm, match_discrim_span);
rptr_ty
} else {
self.check_pat_walk(&inner, tcx.types.err, def_bm, true);
self.check_pat_walk(&inner, tcx.types.err, def_bm, match_discrim_span);
tcx.types.err
}
}
Expand Down Expand Up @@ -427,13 +445,13 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
};

for elt in before {
self.check_pat_walk(&elt, inner_ty, def_bm, true);
self.check_pat_walk(&elt, inner_ty, def_bm, match_discrim_span);
}
if let Some(ref slice) = *slice {
self.check_pat_walk(&slice, slice_ty, def_bm, true);
self.check_pat_walk(&slice, slice_ty, def_bm, match_discrim_span);
}
for elt in after {
self.check_pat_walk(&elt, inner_ty, def_bm, true);
self.check_pat_walk(&elt, inner_ty, def_bm, match_discrim_span);
}
expected_ty
}
Expand Down Expand Up @@ -524,12 +542,14 @@ https://doc.rust-lang.org/reference/types.html#trait-objects");
true
}

pub fn check_match(&self,
expr: &'gcx hir::Expr,
discrim: &'gcx hir::Expr,
arms: &'gcx [hir::Arm],
expected: Expectation<'tcx>,
match_src: hir::MatchSource) -> Ty<'tcx> {
pub fn check_match(
&self,
expr: &'gcx hir::Expr,
discrim: &'gcx hir::Expr,
arms: &'gcx [hir::Arm],
expected: Expectation<'tcx>,
match_src: hir::MatchSource,
) -> Ty<'tcx> {
let tcx = self.tcx;

// Not entirely obvious: if matches may create ref bindings, we want to
Expand Down Expand Up @@ -624,8 +644,12 @@ https://doc.rust-lang.org/reference/types.html#trait-objects");
let mut all_pats_diverge = Diverges::WarnedAlways;
for p in &arm.pats {
self.diverges.set(Diverges::Maybe);
self.check_pat_walk(&p, discrim_ty,
ty::BindingMode::BindByValue(hir::Mutability::MutImmutable), true);
self.check_pat_walk(
&p,
discrim_ty,
ty::BindingMode::BindByValue(hir::Mutability::MutImmutable),
Some(discrim.span),
);
all_pats_diverge &= self.diverges.get();
}

Expand Down Expand Up @@ -703,26 +727,34 @@ https://doc.rust-lang.org/reference/types.html#trait-objects");
coercion.complete(self)
}

fn check_pat_struct(&self,
pat: &'gcx hir::Pat,
qpath: &hir::QPath,
fields: &'gcx [Spanned<hir::FieldPat>],
etc: bool,
expected: Ty<'tcx>,
def_bm: ty::BindingMode) -> Ty<'tcx>
fn check_pat_struct(
&self,
pat: &'gcx hir::Pat,
qpath: &hir::QPath,
fields: &'gcx [Spanned<hir::FieldPat>],
etc: bool,
expected: Ty<'tcx>,
def_bm: ty::BindingMode,
match_discrim_span: Option<Span>,
) -> Ty<'tcx>
{
// Resolve the path and check the definition for errors.
let (variant, pat_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, pat.id) {
variant_ty
} else {
for field in fields {
self.check_pat_walk(&field.node.pat, self.tcx.types.err, def_bm, true);
self.check_pat_walk(
&field.node.pat,
self.tcx.types.err,
def_bm,
match_discrim_span,
);
}
return self.tcx.types.err;
};

// Type-check the path.
self.demand_eqtype(pat.span, expected, pat_ty);
self.demand_eqtype_pat(pat.span, expected, pat_ty, match_discrim_span);

// Type-check subpatterns.
if self.check_struct_pat_fields(pat_ty, pat.id, pat.span, variant, fields, etc, def_bm) {
Expand All @@ -732,11 +764,12 @@ https://doc.rust-lang.org/reference/types.html#trait-objects");
}
}

fn check_pat_path(&self,
pat: &hir::Pat,
qpath: &hir::QPath,
expected: Ty<'tcx>) -> Ty<'tcx>
{
fn check_pat_path(
&self,
pat: &hir::Pat,
qpath: &hir::QPath,
expected: Ty<'tcx>,
) -> Ty<'tcx> {
let tcx = self.tcx;

// Resolve the path and check the definition for errors.
Expand Down Expand Up @@ -767,18 +800,20 @@ https://doc.rust-lang.org/reference/types.html#trait-objects");
pat_ty
}

fn check_pat_tuple_struct(&self,
pat: &hir::Pat,
qpath: &hir::QPath,
subpats: &'gcx [P<hir::Pat>],
ddpos: Option<usize>,
expected: Ty<'tcx>,
def_bm: ty::BindingMode) -> Ty<'tcx>
{
fn check_pat_tuple_struct(
&self,
pat: &hir::Pat,
qpath: &hir::QPath,
subpats: &'gcx [P<hir::Pat>],
ddpos: Option<usize>,
expected: Ty<'tcx>,
def_bm: ty::BindingMode,
match_arm_pat_span: Option<Span>,
) -> Ty<'tcx> {
let tcx = self.tcx;
let on_error = || {
for pat in subpats {
self.check_pat_walk(&pat, tcx.types.err, def_bm, true);
self.check_pat_walk(&pat, tcx.types.err, def_bm, match_arm_pat_span);
}
};
let report_unexpected_def = |def: Def| {
Expand Down Expand Up @@ -826,7 +861,7 @@ https://doc.rust-lang.org/reference/types.html#trait-objects");
let pat_ty = pat_ty.fn_sig(tcx).output();
let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");

self.demand_eqtype(pat.span, expected, pat_ty);
self.demand_eqtype_pat(pat.span, expected, pat_ty, match_arm_pat_span);

// Type-check subpatterns.
if subpats.len() == variant.fields.len() ||
Expand All @@ -837,7 +872,7 @@ https://doc.rust-lang.org/reference/types.html#trait-objects");
};
for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
self.check_pat_walk(&subpat, field_ty, def_bm, true);
self.check_pat_walk(&subpat, field_ty, def_bm, match_arm_pat_span);

self.tcx.check_stability(variant.fields[i].did, Some(pat.id), subpat.span);
}
Expand Down Expand Up @@ -917,7 +952,7 @@ https://doc.rust-lang.org/reference/types.html#trait-objects");
}
};

self.check_pat_walk(&field.pat, field_ty, def_bm, true);
self.check_pat_walk(&field.pat, field_ty, def_bm, None);
}
let mut unmentioned_fields = variant.fields
.iter()
Expand Down
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