Auto merge of #13523 - lowr:fix/adjust-expectation-for-if, r=lnicola

fix: disregard type variable expectation for if expressions

Fixes #13522

As [the comment](https://github.com/rust-lang/rust-analyzer/blob/8142d1f606dc2e52b1d2b8992671e2bd73379f28/crates/hir-ty/src/infer.rs#L1087-L1090) on `Expectation::adjust_for_branches` explains:

> 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.

Note that we already use it in match expressions. I've added tests for them too nevertheless.

2 files changed, 34 insertions, 0 deletions

diff --git a/crates/hir-ty/src/infer/expr.rs b/crates/hir-ty/src/infer/expr.rs
index f56108b26c4..b1f4de82607 100644
--- a/crates/hir-ty/src/infer/expr.rs
+++ b/crates/hir-ty/src/infer/expr.rs
@@ -85,6 +85,7 @@ impl<'a> InferenceContext<'a> {
         let ty = match &self.body[tgt_expr] {
             Expr::Missing => self.err_ty(),
             &Expr::If { condition, then_branch, else_branch } => {
+                let expected = &expected.adjust_for_branches(&mut self.table);
                 self.infer_expr(
                     condition,
                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
diff --git a/crates/hir-ty/src/tests/coercion.rs b/crates/hir-ty/src/tests/coercion.rs
index d301595bcd9..1abdb0be7f8 100644
--- a/crates/hir-ty/src/tests/coercion.rs
+++ b/crates/hir-ty/src/tests/coercion.rs
@@ -123,6 +123,23 @@ fn test() {
 }
 
 #[test]
+fn if_else_adjust_for_branches_discard_type_var() {
+    check_no_mismatches(
+        r#"
+fn test() {
+    let f = || {
+        if true {
+            &""
+        } else {
+            ""
+        }
+    };
+}
+"#,
+    );
+}
+
+#[test]
 fn match_first_coerce() {
     check_no_mismatches(
         r#"
@@ -183,6 +200,22 @@ fn test() {
 }
 
 #[test]
+fn match_adjust_for_branches_discard_type_var() {
+    check_no_mismatches(
+        r#"
+fn test() {
+    let f = || {
+        match 0i32 {
+            0i32 => &"",
+            _ => "",
+        }
+    };
+}
+"#,
+    );
+}
+
+#[test]
 fn return_coerce_unknown() {
     check_types(
         r"