Fix if in rust-lang#11561

Author: ChayimFriedman2

crates/syntax/src/ast/expr_ext.rs

@@ -49,25 +49,81 @@ impl From<ast::IfExpr> for ElseBranch {
 
 impl ast::IfExpr {
     pub fn then_branch(&self) -> Option<ast::BlockExpr> {
-        self.blocks().next()
+        self.children_after_condition().next()
     }
 
     pub fn else_branch(&self) -> Option<ElseBranch> {
-        let res = match self.blocks().nth(1) {
+        let res = match self.children_after_condition().nth(1) {
             Some(block) => ElseBranch::Block(block),
             None => {
-                let elif: ast::IfExpr = support::child(self.syntax())?;
+                let elif = self.children_after_condition().next()?;
                 ElseBranch::IfExpr(elif)
             }
         };
         Some(res)
     }
 
-    pub fn blocks(&self) -> AstChildren<ast::BlockExpr> {
-        support::children(self.syntax())
+    fn children_after_condition<N: AstNode>(&self) -> impl Iterator<Item = N> {
+        self.syntax().children().skip(1).filter_map(N::cast)
     }
 }
 
+#[test]
+fn if_block_condition() {
+    let parse = ast::SourceFile::parse(
+        r#"
+        fn test() {
+            if { true } { "if" }
+            else if { false } { "first elif" }
+            else if true { "second elif" }
+            else if (true) { "third elif" }
+            else { "else" }
+        }
+        "#,
+    );
+    let if_ = parse.tree().syntax().descendants().find_map(ast::IfExpr::cast).unwrap();
+    assert_eq!(if_.then_branch().unwrap().syntax().text(), r#"{ "if" }"#);
+    let elif = match if_.else_branch().unwrap() {
+        ElseBranch::IfExpr(elif) => elif,
+        ElseBranch::Block(_) => panic!("should be `else if`"),
+    };
+    assert_eq!(elif.then_branch().unwrap().syntax().text(), r#"{ "first elif" }"#);
+    let elif = match elif.else_branch().unwrap() {
+        ElseBranch::IfExpr(elif) => elif,
+        ElseBranch::Block(_) => panic!("should be `else if`"),
+    };
+    assert_eq!(elif.then_branch().unwrap().syntax().text(), r#"{ "second elif" }"#);
+    let elif = match elif.else_branch().unwrap() {
+        ElseBranch::IfExpr(elif) => elif,
+        ElseBranch::Block(_) => panic!("should be `else if`"),
+    };
+    assert_eq!(elif.then_branch().unwrap().syntax().text(), r#"{ "third elif" }"#);
+    let else_ = match elif.else_branch().unwrap() {
+        ElseBranch::Block(else_) => else_,
+        ElseBranch::IfExpr(_) => panic!("should be `else`"),
+    };
+    assert_eq!(else_.syntax().text(), r#"{ "else" }"#);
+}
+
+#[test]
+fn if_condition_with_if_inside() {
+    let parse = ast::SourceFile::parse(
+        r#"
+        fn test() {
+            if if true { true } else { false } { "if" }
+            else { "else" }
+        }
+        "#,
+    );
+    let if_ = parse.tree().syntax().descendants().find_map(ast::IfExpr::cast).unwrap();
+    assert_eq!(if_.then_branch().unwrap().syntax().text(), r#"{ "if" }"#);
+    let else_ = match if_.else_branch().unwrap() {
+        ElseBranch::Block(else_) => else_,
+        ElseBranch::IfExpr(_) => panic!("should be `else`"),
+    };
+    assert_eq!(else_.syntax().text(), r#"{ "else" }"#);
+}
+
 impl ast::PrefixExpr {
     pub fn op_kind(&self) -> Option<UnaryOp> {
         let res = match self.op_token()?.kind() {