Fix coercion in match with expected type

Plus add infrastructure to test type mismatches without expect.

crates/base_db/src/lib.rs

@@ -42,7 +42,7 @@ pub struct FilePosition {
     pub offset: TextSize,
 }
 
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash)]
 pub struct FileRange {
     pub file_id: FileId,
     pub range: TextRange,

crates/hir_ty/src/infer.rs

@@ -761,6 +761,38 @@ fn only_has_type(&self, table: &mut unify::InferenceTable) -> Option<Ty> {
             Expectation::RValueLikeUnsized(_) | Expectation::None => None,
         }
     }
+
+    /// Comment copied from rustc:
+    /// Disregard "castable to" expectations because they
+    /// can lead us astray. Consider for example `if cond
+    /// {22} else {c} as u8` -- if we propagate the
+    /// "castable to u8" constraint to 22, it will pick the
+    /// type 22u8, which is overly constrained (c might not
+    /// be a u8). In effect, the problem is that the
+    /// "castable to" expectation is not the tightest thing
+    /// we can say, so we want to drop it in this case.
+    /// The tightest thing we can say is "must unify with
+    /// else branch". Note that in the case of a "has type"
+    /// constraint, this limitation does not hold.
+    ///
+    /// If the expected type is just a type variable, then don't use
+    /// an expected type. Otherwise, we might write parts of the type
+    /// when checking the 'then' block which are incompatible with the
+    /// 'else' branch.
+    fn adjust_for_branches(&self, table: &mut unify::InferenceTable) -> Expectation {
+        match self {
+            Expectation::HasType(ety) => {
+                let ety = table.resolve_ty_shallow(&ety);
+                if !ety.is_ty_var() {
+                    Expectation::HasType(ety)
+                } else {
+                    Expectation::None
+                }
+            }
+            Expectation::RValueLikeUnsized(ety) => Expectation::RValueLikeUnsized(ety.clone()),
+            _ => Expectation::None,
+        }
+    }
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]

crates/hir_ty/src/infer/expr.rs

@@ -337,10 +337,15 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
             Expr::Match { expr, arms } => {
                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 
+                let expected = expected.adjust_for_branches(&mut self.table);
+
                 let mut result_ty = if arms.is_empty() {
                     TyKind::Never.intern(&Interner)
                 } else {
-                    self.table.new_type_var()
+                    match &expected {
+                        Expectation::HasType(ty) => ty.clone(),
+                        _ => self.table.new_type_var(),
+                    }
                 };
 
                 let matchee_diverges = self.diverges;

crates/hir_ty/src/tests.rs

@@ -9,7 +9,7 @@
 mod display_source_code;
 mod incremental;
 
-use std::{env, sync::Arc};
+use std::{collections::HashMap, env, sync::Arc};
 
 use base_db::{fixture::WithFixture, FileRange, SourceDatabase, SourceDatabaseExt};
 use expect_test::Expect;
@@ -83,9 +83,105 @@ fn check_types_impl(ra_fixture: &str, display_source: bool) {
             checked_one = true;
         }
     }
+
     assert!(checked_one, "no `//^` annotations found");
 }
 
+fn check_no_mismatches(ra_fixture: &str) {
+    check_mismatches_impl(ra_fixture, true)
+}
+
+#[allow(unused)]
+fn check_mismatches(ra_fixture: &str) {
+    check_mismatches_impl(ra_fixture, false)
+}
+
+fn check_mismatches_impl(ra_fixture: &str, allow_none: bool) {
+    let _tracing = setup_tracing();
+    let (db, file_id) = TestDB::with_single_file(ra_fixture);
+    let module = db.module_for_file(file_id);
+    let def_map = module.def_map(&db);
+
+    let mut defs: Vec<DefWithBodyId> = Vec::new();
+    visit_module(&db, &def_map, module.local_id, &mut |it| defs.push(it));
+    defs.sort_by_key(|def| match def {
+        DefWithBodyId::FunctionId(it) => {
+            let loc = it.lookup(&db);
+            loc.source(&db).value.syntax().text_range().start()
+        }
+        DefWithBodyId::ConstId(it) => {
+            let loc = it.lookup(&db);
+            loc.source(&db).value.syntax().text_range().start()
+        }
+        DefWithBodyId::StaticId(it) => {
+            let loc = it.lookup(&db);
+            loc.source(&db).value.syntax().text_range().start()
+        }
+    });
+    let mut mismatches = HashMap::new();
+    let mut push_mismatch = |src_ptr: InFile<SyntaxNode>, mismatch: TypeMismatch| {
+        let range = src_ptr.value.text_range();
+        if src_ptr.file_id.call_node(&db).is_some() {
+            panic!("type mismatch in macro expansion");
+        }
+        let file_range = FileRange { file_id: src_ptr.file_id.original_file(&db), range };
+        let actual = format!(
+            "expected {}, got {}",
+            mismatch.expected.display_test(&db),
+            mismatch.actual.display_test(&db)
+        );
+        mismatches.insert(file_range, actual);
+    };
+    for def in defs {
+        let (_body, body_source_map) = db.body_with_source_map(def);
+        let inference_result = db.infer(def);
+        for (pat, mismatch) in inference_result.pat_type_mismatches() {
+            let syntax_ptr = match body_source_map.pat_syntax(pat) {
+                Ok(sp) => {
+                    let root = db.parse_or_expand(sp.file_id).unwrap();
+                    sp.map(|ptr| {
+                        ptr.either(
+                            |it| it.to_node(&root).syntax().clone(),
+                            |it| it.to_node(&root).syntax().clone(),
+                        )
+                    })
+                }
+                Err(SyntheticSyntax) => continue,
+            };
+            push_mismatch(syntax_ptr, mismatch.clone());
+        }
+        for (expr, mismatch) in inference_result.expr_type_mismatches() {
+            let node = match body_source_map.expr_syntax(expr) {
+                Ok(sp) => {
+                    let root = db.parse_or_expand(sp.file_id).unwrap();
+                    sp.map(|ptr| ptr.to_node(&root).syntax().clone())
+                }
+                Err(SyntheticSyntax) => continue,
+            };
+            push_mismatch(node, mismatch.clone());
+        }
+    }
+    let mut checked_one = false;
+    for (file_id, annotations) in db.extract_annotations() {
+        for (range, expected) in annotations {
+            let file_range = FileRange { file_id, range };
+            if let Some(mismatch) = mismatches.remove(&file_range) {
+                assert_eq!(mismatch, expected);
+            } else {
+                assert!(false, "Expected mismatch not encountered: {}\n", expected);
+            }
+            checked_one = true;
+        }
+    }
+    let mut buf = String::new();
+    for (range, mismatch) in mismatches {
+        format_to!(buf, "{:?}: {}\n", range.range, mismatch,);
+    }
+    assert!(buf.is_empty(), "Unexpected type mismatches:\n{}", buf);
+
+    assert!(checked_one || allow_none, "no `//^` annotations found");
+}
+
 fn type_at_range(db: &TestDB, pos: FileRange) -> Ty {
     let file = db.parse(pos.file_id).ok().unwrap();
     let expr = algo::find_node_at_range::<ast::Expr>(file.syntax(), pos.range).unwrap();

crates/hir_ty/src/tests/coercion.rs

@@ -1,6 +1,6 @@
 use expect_test::expect;
 
-use super::{check_infer, check_infer_with_mismatches, check_types};
+use super::{check_infer, check_infer_with_mismatches, check_no_mismatches, check_types};
 
 #[test]
 fn infer_block_expr_type_mismatch() {
@@ -963,7 +963,7 @@ fn test() -> i32 {
 
 #[test]
 fn panic_macro() {
-    check_infer_with_mismatches(
+    check_no_mismatches(
         r#"
 mod panic {
     #[macro_export]
@@ -991,15 +991,34 @@ fn main() {
     panic!()
 }
         "#,
-        expect![[r#"
-            174..185 '{ loop {} }': !
-            176..183 'loop {}': !
-            181..183 '{}': ()
-            !0..24 '$crate...:panic': fn panic() -> !
-            !0..26 '$crate...anic()': !
-            !0..26 '$crate...anic()': !
-            !0..28 '$crate...015!()': !
-            454..470 '{     ...c!() }': ()
-        "#]],
+    );
+}
+
+#[test]
+fn coerce_unsize_expected_type() {
+    check_no_mismatches(
+        r#"
+#[lang = "sized"]
+pub trait Sized {}
+#[lang = "unsize"]
+pub trait Unsize<T> {}
+#[lang = "coerce_unsized"]
+pub trait CoerceUnsized<T> {}
+
+impl<T: Unsize<U>, U> CoerceUnsized<&U> for &T {}
+
+fn main() {
+    let foo: &[u32] = &[1, 2];
+    let foo: &[u32] = match true {
+        true => &[1, 2],
+        false => &[1, 2, 3],
+    };
+    let foo: &[u32] = if true {
+        &[1, 2]
+    } else {
+        &[1, 2, 3]
+    };
+}
+        "#,
     );
 }

crates/hir_ty/src/tests/patterns.rs

@@ -1,6 +1,6 @@
 use expect_test::expect;
 
-use super::{check_infer, check_infer_with_mismatches, check_types};
+use super::{check_infer, check_infer_with_mismatches, check_mismatches, check_types};
 
 #[test]
 fn infer_pattern() {
@@ -518,47 +518,24 @@ fn test(a1: A<u32>, o: Option<u64>) {
 
 #[test]
 fn infer_const_pattern() {
-    check_infer_with_mismatches(
+    check_mismatches(
         r#"
-        enum Option<T> { None }
-        use Option::None;
-        struct Foo;
-        const Bar: usize = 1;
+enum Option<T> { None }
+use Option::None;
+struct Foo;
+const Bar: usize = 1;
 
-        fn test() {
-            let a: Option<u32> = None;
-            let b: Option<i64> = match a {
-                None => None,
-            };
-            let _: () = match () { Foo => Foo }; // Expected mismatch
-            let _: () = match () { Bar => Bar }; // Expected mismatch
-        }
+fn test() {
+    let a: Option<u32> = None;
+    let b: Option<i64> = match a {
+        None => None,
+    };
+    let _: () = match () { Foo => () };
+                        // ^^^ expected (), got Foo
+    let _: () = match () { Bar => () };
+                        // ^^^ expected (), got usize
+}
         "#,
-        expect![[r#"
-            73..74 '1': usize
-            87..309 '{     ...atch }': ()
-            97..98 'a': Option<u32>
-            114..118 'None': Option<u32>
-            128..129 'b': Option<i64>
-            145..182 'match ...     }': Option<i64>
-            151..152 'a': Option<u32>
-            163..167 'None': Option<u32>
-            171..175 'None': Option<i64>
-            192..193 '_': ()
-            200..223 'match ... Foo }': Foo
-            206..208 '()': ()
-            211..214 'Foo': Foo
-            218..221 'Foo': Foo
-            254..255 '_': ()
-            262..285 'match ... Bar }': usize
-            268..270 '()': ()
-            273..276 'Bar': usize
-            280..283 'Bar': usize
-            200..223: expected (), got Foo
-            211..214: expected (), got Foo
-            262..285: expected (), got usize
-            273..276: expected (), got usize
-        "#]],
     );
 }