Fix assertion error in unification (hopefully)

Currently, all types that we handle during inference need to be resolved as far
as possible at the time. It's maybe too brittle of an invariant; I need to think
how we can do this better. This should fix #484 though, I hope (if
it's the same case as I managed to reproduce).

diff --git a/crates/ra_hir/src/ty.rs b/crates/ra_hir/src/ty.rs
index 0c24a065270f0f58d95a1c970f8625b45c68d8dc..2d533eb6a9157ccd1a07267ecf7fc37ff255f861 100644 (file)
--- a/crates/ra_hir/src/ty.rs
+++ b/crates/ra_hir/src/ty.rs
@@ -18,6 +18,7 @@
 #[cfg(test)]
 mod tests;
 
+use std::borrow::Cow;
 use std::ops::Index;
 use std::sync::Arc;
 use std::{fmt, mem};
@@ -671,7 +672,10 @@ fn make_ty(&self, type_ref: &TypeRef) -> Cancelable<Ty> {
     }
 
     fn unify(&mut self, ty1: &Ty, ty2: &Ty) -> bool {
-        match (ty1, ty2) {
+        // try to resolve type vars first
+        let ty1 = self.resolve_ty_shallow(ty1);
+        let ty2 = self.resolve_ty_shallow(ty2);
+        match (&*ty1, &*ty2) {
             (Ty::Unknown, ..) => true,
             (.., Ty::Unknown) => true,
             (Ty::Bool, _)
@@ -698,10 +702,12 @@ fn unify(&mut self, ty1: &Ty, ty2: &Ty) -> bool {
                 .zip(ts2.iter())
                 .all(|(t1, t2)| self.unify(t1, t2)),
             (Ty::Infer(InferTy::TypeVar(tv1)), Ty::Infer(InferTy::TypeVar(tv2))) => {
+                // both type vars are unknown since we tried to resolve them
                 self.var_unification_table.union(*tv1, *tv2);
                 true
             }
             (Ty::Infer(InferTy::TypeVar(tv)), other) | (other, Ty::Infer(InferTy::TypeVar(tv))) => {
+                // the type var is unknown since we tried to resolve it
                 self.var_unification_table
                     .union_value(*tv, TypeVarValue::Known(other.clone()));
                 true
@@ -746,6 +752,23 @@ fn resolve_ty_as_possible(&mut self, ty: Ty) -> Ty {
         })
     }
 
+    /// If `ty` is a type variable with known type, returns that type;
+    /// otherwise, return ty.
+    fn resolve_ty_shallow<'b>(&mut self, ty: &'b Ty) -> Cow<'b, Ty> {
+        match ty {
+            Ty::Infer(InferTy::TypeVar(tv)) => {
+                match self.var_unification_table.probe_value(*tv).known() {
+                    Some(known_ty) => {
+                        // The known_ty can't be a type var itself
+                        Cow::Owned(known_ty.clone())
+                    }
+                    _ => Cow::Borrowed(ty),
+                }
+            }
+            _ => Cow::Borrowed(ty),
+        }
+    }
+
     /// Resolves the type completely; type variables without known type are
     /// replaced by Ty::Unknown.
     fn resolve_ty_completely(&mut self, ty: Ty) -> Ty {
@@ -816,12 +839,15 @@ fn infer_expr(&mut self, expr: ExprId, expected: &Expectation) -> Cancelable<Ty>
                 // if let is desugared to match, so this is always simple if
                 self.infer_expr(*condition, &Expectation::has_type(Ty::Bool))?;
                 let then_ty = self.infer_expr(*then_branch, expected)?;
-                if let Some(else_branch) = else_branch {
-                    self.infer_expr(*else_branch, expected)?;
-                } else {
-                    // no else branch -> unit
-                    self.unify(&expected.ty, &Ty::unit()); // actually coerce
-                }
+                match else_branch {
+                    Some(else_branch) => {
+                        self.infer_expr(*else_branch, expected)?;
+                    }
+                    None => {
+                        // no else branch -> unit
+                        self.unify(&then_ty, &Ty::unit()); // actually coerce
+                    }
+                };
                 then_ty
             }
             Expr::Block { statements, tail } => self.infer_block(statements, *tail, expected)?,

diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index d8c0af32682d71fc0bbde62f01dca67bc0eb888b..815aecda76cc8bd28257bad707b30bab32138297 100644 (file)
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -230,6 +230,18 @@ fn test2(a1: *const A, a2: *mut A) {
     );
 }
 
+#[test]
+fn infer_bug_484() {
+    check_inference(
+        r#"
+fn test() {
+   let x = if true {};
+}
+"#,
+        "bug_484.txt",
+    );
+}
+
 fn infer(content: &str) -> String {
     let (db, _, file_id) = MockDatabase::with_single_file(content);
     let source_file = db.source_file(file_id);

diff --git a/crates/ra_hir/src/ty/tests/data/bug_484.txt b/crates/ra_hir/src/ty/tests/data/bug_484.txt
new file mode 100644 (file)
index 0000000..3005305
--- /dev/null
+++ b/crates/ra_hir/src/ty/tests/data/bug_484.txt
@@ -0,0 +1,5 @@
+[11; 37) '{    l... {}; }': ()
+[20; 21) 'x': ()
+[24; 34) 'if true {}': ()
+[27; 31) 'true': bool
+[32; 34) '{}': ()