Implement parsing for tuple accessor functions (.1, .2, etc)

Step 2 of N toward implementing #4465

crates/compiler/parse/src/ast.rs

@@ -163,13 +163,19 @@ pub enum Expr<'a> {
 
     // String Literals
     Str(StrLiteral<'a>), // string without escapes in it
-    /// Look up exactly one field on a record, e.g. (expr).foo.
-    Access(&'a Expr<'a>, &'a str),
-    /// e.g. `.foo`
-    AccessorFunction(&'a str),
     /// eg 'b'
     SingleQuote(&'a str),
 
+    /// Look up exactly one field on a record, e.g. `x.foo`.
+    RecordAccess(&'a Expr<'a>, &'a str),
+    /// e.g. `.foo`
+    RecordAccessorFunction(&'a str),
+
+    /// Look up exactly one field on a tuple, e.g. `(x, y).1`.
+    TupleAccess(&'a Expr<'a>, &'a str),
+    /// e.g. `.1`
+    TupleAccessorFunction(&'a str),
+
     // Collection Literals
     List(Collection<'a, &'a Loc<Expr<'a>>>),
 
@@ -731,7 +737,8 @@ impl<'a> Pattern<'a> {
                     Pattern::Malformed(buf.into_bump_str())
                 }
             }
-            Ident::AccessorFunction(string) => Pattern::Malformed(string),
+            Ident::RecordAccessorFunction(string) => Pattern::Malformed(string),
+            Ident::TupleAccessorFunction(string) => Pattern::Malformed(string),
             Ident::Malformed(string, _problem) => Pattern::Malformed(string),
         }
     }