handle tuple patterns with ellipsis

JoshMcguigan · JoshMcguigan · commit ee822d19b766 · 2020-04-13T08:19:19.000-07:00
diff --git a/crates/ra_hir_def/src/body/lower.rs b/crates/ra_hir_def/src/body/lower.rs
@@ -33,6 +33,7 @@ use crate::{
 };
 
 use super::{ExprSource, PatSource};
+use ast::AstChildren;
 
 pub(super) fn lower(
     db: &dyn DefDatabase,
@@ -598,8 +599,8 @@ impl ExprCollector<'_> {
             }
             ast::Pat::TupleStructPat(p) => {
                 let path = p.path().and_then(|path| self.expander.parse_path(path));
-                let args = p.args().map(|p| self.collect_pat(p)).collect();
-                Pat::TupleStruct { path, args }
+                let (args, ellipsis) = self.collect_tuple_pat(p.args());
+                Pat::TupleStruct { path, args, ellipsis }
             }
             ast::Pat::RefPat(p) => {
                 let pat = self.collect_pat_opt(p.pat());
@@ -616,10 +617,10 @@ impl ExprCollector<'_> {
             }
             ast::Pat::ParenPat(p) => return self.collect_pat_opt(p.pat()),
             ast::Pat::TuplePat(p) => {
-                let args = p.args().map(|p| self.collect_pat(p)).collect();
-                Pat::Tuple(args)
+                let (args, ellipsis) = self.collect_tuple_pat(p.args());
+                Pat::Tuple { args, ellipsis }
             }
-            ast::Pat::PlaceholderPat(_) | ast::Pat::DotDotPat(_) => Pat::Wild,
+            ast::Pat::PlaceholderPat(_) => Pat::Wild,
             ast::Pat::RecordPat(p) => {
                 let path = p.path().and_then(|path| self.expander.parse_path(path));
                 let record_field_pat_list =
@@ -665,6 +666,9 @@ impl ExprCollector<'_> {
                     Pat::Missing
                 }
             }
+            ast::Pat::DotDotPat(_) => unreachable!(
+                "`DotDotPat` requires special handling and should not be mapped to a Pat."
+            ),
             // FIXME: implement
             ast::Pat::BoxPat(_) | ast::Pat::RangePat(_) | ast::Pat::MacroPat(_) => Pat::Missing,
         };
@@ -679,6 +683,19 @@ impl ExprCollector<'_> {
             self.missing_pat()
         }
     }
+
+    fn collect_tuple_pat(&mut self, args: AstChildren<ast::Pat>) -> (Vec<PatId>, Option<usize>) {
+        // Find the location of the `..`, if there is one. Note that we do not
+        // consider the possiblity of there being multiple `..` here.
+        let ellipsis = args.clone().position(|p| matches!(p, ast::Pat::DotDotPat(_)));
+        // We want to skip the `..` pattern here, since we account for it above.
+        let args = args
+            .filter(|p| !matches!(p, ast::Pat::DotDotPat(_)))
+            .map(|p| self.collect_pat(p))
+            .collect();
+
+        (args, ellipsis)
+    }
 }
 
 impl From<ast::BinOp> for BinaryOp {
diff --git a/crates/ra_hir_def/src/expr.rs b/crates/ra_hir_def/src/expr.rs
@@ -374,15 +374,15 @@ pub struct RecordFieldPat {
 pub enum Pat {
     Missing,
     Wild,
-    Tuple(Vec<PatId>),
+    Tuple { args: Vec<PatId>, ellipsis: Option<usize> },
     Or(Vec<PatId>),
     Record { path: Option<Path>, args: Vec<RecordFieldPat>, ellipsis: bool },
     Range { start: ExprId, end: ExprId },
     Slice { prefix: Vec<PatId>, slice: Option<PatId>, suffix: Vec<PatId> },
     Path(Path),
     Lit(ExprId),
     Bind { mode: BindingAnnotation, name: Name, subpat: Option<PatId> },
-    TupleStruct { path: Option<Path>, args: Vec<PatId> },
+    TupleStruct { path: Option<Path>, args: Vec<PatId>, ellipsis: Option<usize> },
     Ref { pat: PatId, mutability: Mutability },
 }
 
@@ -393,7 +393,7 @@ impl Pat {
             Pat::Bind { subpat, .. } => {
                 subpat.iter().copied().for_each(f);
             }
-            Pat::Or(args) | Pat::Tuple(args) | Pat::TupleStruct { args, .. } => {
+            Pat::Or(args) | Pat::Tuple { args, .. } | Pat::TupleStruct { args, .. } => {
                 args.iter().copied().for_each(f);
             }
             Pat::Ref { pat, .. } => f(*pat),
diff --git a/crates/ra_hir_ty/src/_match.rs b/crates/ra_hir_ty/src/_match.rs
@@ -289,7 +289,7 @@ impl PatStack {
         Self::from_slice(&self.0[1..])
     }
 
-    fn replace_head_with(&self, pat_ids: &[PatId]) -> PatStack {
+    fn replace_head_with<T: Into<PatIdOrWild> + Copy>(&self, pat_ids: &[T]) -> PatStack {
         let mut patterns: PatStackInner = smallvec![];
         for pat in pat_ids {
             patterns.push((*pat).into());
@@ -320,12 +320,14 @@ impl PatStack {
         constructor: &Constructor,
     ) -> MatchCheckResult<Option<PatStack>> {
         let result = match (self.head().as_pat(cx), constructor) {
-            (Pat::Tuple(ref pat_ids), Constructor::Tuple { arity }) => {
-                debug_assert_eq!(
-                    pat_ids.len(),
-                    *arity,
-                    "we type check before calling this code, so we should never hit this case",
-                );
+            (Pat::Tuple { args: ref pat_ids, ellipsis }, Constructor::Tuple { arity: _ }) => {
+                if ellipsis.is_some() {
+                    // If there are ellipsis here, we should add the correct number of
+                    // Pat::Wild patterns to `pat_ids`. We should be able to use the
+                    // constructors arity for this, but at the time of writing we aren't
+                    // correctly calculating this arity when ellipsis are present.
+                    return Err(MatchCheckErr::NotImplemented);
+                }
 
                 Some(self.replace_head_with(pat_ids))
             }
@@ -351,19 +353,47 @@ impl PatStack {
                     Some(self.to_tail())
                 }
             }
-            (Pat::TupleStruct { args: ref pat_ids, .. }, Constructor::Enum(enum_constructor)) => {
+            (
+                Pat::TupleStruct { args: ref pat_ids, ellipsis, .. },
+                Constructor::Enum(enum_constructor),
+            ) => {
                 let pat_id = self.head().as_id().expect("we know this isn't a wild");
                 if !enum_variant_matches(cx, pat_id, *enum_constructor) {
                     None
                 } else {
-                    // If the enum variant matches, then we need to confirm
-                    // that the number of patterns aligns with the expected
-                    // number of patterns for that enum variant.
-                    if pat_ids.len() != constructor.arity(cx)? {
-                        return Err(MatchCheckErr::MalformedMatchArm);
+                    let constructor_arity = constructor.arity(cx)?;
+                    if let Some(ellipsis_position) = ellipsis {
+                        // If there are ellipsis in the pattern, the ellipsis must take the place
+                        // of at least one sub-pattern, so `pat_ids` should be smaller than the
+                        // constructor arity.
+                        if pat_ids.len() < constructor_arity {
+                            let mut new_patterns: Vec<PatIdOrWild> = vec![];
+
+                            for pat_id in &pat_ids[0..ellipsis_position] {
+                                new_patterns.push((*pat_id).into());
+                            }
+
+                            for _ in 0..(constructor_arity - pat_ids.len()) {
+                                new_patterns.push(PatIdOrWild::Wild);
+                            }
+
+                            for pat_id in &pat_ids[ellipsis_position..pat_ids.len()] {
+                                new_patterns.push((*pat_id).into());
+                            }
+
+                            Some(self.replace_head_with(&new_patterns))
+                        } else {
+                            return Err(MatchCheckErr::MalformedMatchArm);
+                        }
+                    } else {
+                        // If there is no ellipsis in the tuple pattern, the number
+                        // of patterns must equal the constructor arity.
+                        if pat_ids.len() == constructor_arity {
+                            Some(self.replace_head_with(pat_ids))
+                        } else {
+                            return Err(MatchCheckErr::MalformedMatchArm);
+                        }
                     }
-
-                    Some(self.replace_head_with(pat_ids))
                 }
             }
             (Pat::Or(_), _) => return Err(MatchCheckErr::NotImplemented),
@@ -644,7 +674,11 @@ impl Constructor {
 fn pat_constructor(cx: &MatchCheckCtx, pat: PatIdOrWild) -> MatchCheckResult<Option<Constructor>> {
     let res = match pat.as_pat(cx) {
         Pat::Wild => None,
-        Pat::Tuple(pats) => Some(Constructor::Tuple { arity: pats.len() }),
+        // FIXME somehow create the Tuple constructor with the proper arity. If there are
+        // ellipsis, the arity is not equal to the number of patterns.
+        Pat::Tuple { args: pats, ellipsis } if ellipsis.is_none() => {
+            Some(Constructor::Tuple { arity: pats.len() })
+        }
         Pat::Lit(lit_expr) => match cx.body.exprs[lit_expr] {
             Expr::Literal(Literal::Bool(val)) => Some(Constructor::Bool(val)),
             _ => return Err(MatchCheckErr::NotImplemented),
@@ -1506,6 +1540,67 @@ mod tests {
         check_no_diagnostic(content);
     }
 
+    #[test]
+    fn enum_tuple_partial_ellipsis_2_no_diagnostic() {
+        let content = r"
+            enum Either {
+                A(bool, bool, bool, bool),
+                B,
+            }
+            fn test_fn() {
+                match Either::B {
+                    Either::A(true, .., true) => {},
+                    Either::A(true, .., false) => {},
+                    Either::A(.., true) => {},
+                    Either::A(.., false) => {},
+                    Either::B => {},
+                }
+            }
+        ";
+
+        check_no_diagnostic(content);
+    }
+
+    #[test]
+    fn enum_tuple_partial_ellipsis_missing_arm() {
+        let content = r"
+            enum Either {
+                A(bool, bool, bool, bool),
+                B,
+            }
+            fn test_fn() {
+                match Either::B {
+                    Either::A(true, .., true) => {},
+                    Either::A(true, .., false) => {},
+                    Either::A(false, .., false) => {},
+                    Either::B => {},
+                }
+            }
+        ";
+
+        check_diagnostic(content);
+    }
+
+    #[test]
+    fn enum_tuple_partial_ellipsis_2_missing_arm() {
+        let content = r"
+            enum Either {
+                A(bool, bool, bool, bool),
+                B,
+            }
+            fn test_fn() {
+                match Either::B {
+                    Either::A(true, .., true) => {},
+                    Either::A(true, .., false) => {},
+                    Either::A(.., true) => {},
+                    Either::B => {},
+                }
+            }
+        ";
+
+        check_diagnostic(content);
+    }
+
     #[test]
     fn enum_tuple_ellipsis_no_diagnostic() {
         let content = r"
@@ -1645,11 +1740,7 @@ mod false_negatives {
         ";
 
         // This is a false negative.
-        // The `..` pattern is currently lowered to a single `Pat::Wild`
-        // no matter how many fields the `..` pattern is covering. This
-        // causes the match arm in this test not to type check against
-        // the match expression, which causes this diagnostic not to
-        // fire.
+        // We don't currently handle tuple patterns with ellipsis.
         check_no_diagnostic(content);
     }
 
@@ -1664,32 +1755,7 @@ mod false_negatives {
         ";
 
         // This is a false negative.
-        // See comments on `tuple_of_bools_with_ellipsis_at_end_missing_arm`.
-        check_no_diagnostic(content);
-    }
-
-    #[test]
-    fn enum_tuple_partial_ellipsis_missing_arm() {
-        let content = r"
-            enum Either {
-                A(bool, bool, bool, bool),
-                B,
-            }
-            fn test_fn() {
-                match Either::B {
-                    Either::A(true, .., true) => {},
-                    Either::A(true, .., false) => {},
-                    Either::A(false, .., false) => {},
-                    Either::B => {},
-                }
-            }
-        ";
-
-        // This is a false negative.
-        // The `..` pattern is currently lowered to a single `Pat::Wild`
-        // no matter how many fields the `..` pattern is covering. This
-        // causes us to return a `MatchCheckErr::MalformedMatchArm` in
-        // `Pat::specialize_constructor`.
+        // We don't currently handle tuple patterns with ellipsis.
         check_no_diagnostic(content);
     }
 }
diff --git a/crates/ra_hir_ty/src/infer/pat.rs b/crates/ra_hir_ty/src/infer/pat.rs
@@ -85,7 +85,7 @@ impl<'a> InferenceContext<'a> {
         let body = Arc::clone(&self.body); // avoid borrow checker problem
 
         let is_non_ref_pat = match &body[pat] {
-            Pat::Tuple(..)
+            Pat::Tuple { .. }
             | Pat::Or(..)
             | Pat::TupleStruct { .. }
             | Pat::Record { .. }
@@ -116,7 +116,7 @@ impl<'a> InferenceContext<'a> {
         let expected = expected;
 
         let ty = match &body[pat] {
-            Pat::Tuple(ref args) => {
+            Pat::Tuple { ref args, .. } => {
                 let expectations = match expected.as_tuple() {
                     Some(parameters) => &*parameters.0,
                     _ => &[],
@@ -155,7 +155,7 @@ impl<'a> InferenceContext<'a> {
                 let subty = self.infer_pat(*pat, expectation, default_bm);
                 Ty::apply_one(TypeCtor::Ref(*mutability), subty)
             }
-            Pat::TupleStruct { path: p, args: subpats } => {
+            Pat::TupleStruct { path: p, args: subpats, .. } => {
                 self.infer_tuple_struct_pat(p.as_ref(), subpats, expected, default_bm, pat)
             }
             Pat::Record { path: p, args: fields, ellipsis: _ } => {
