introduce hacks module

crates/syntax/src/hacks.rs

@@ -0,0 +1,14 @@
+//! Things which exist to solve practial issues, but which shouldn't exist.
+//!
+//! Please avoid adding new usages of the functions in this module
+
+use crate::{ast, AstNode};
+
+pub fn parse_expr_from_str(s: &str) -> Option<ast::Expr> {
+    let file = ast::SourceFile::parse(&format!("const _: () = {};", s));
+    let expr = file.syntax_node().descendants().find_map(ast::Expr::cast)?;
+    if expr.syntax().text() != s {
+        return None;
+    }
+    Some(expr)
+}