cli: positional arguments are invalid when parsing configuration

src/cli/diagnostics.zig

@@ -46,6 +46,8 @@ pub const Location = union(enum) {
         line: usize,
     },
 
+    pub const Key = @typeInfo(Location).Union.tag_type.?;
+
     pub fn fromIter(iter: anytype) Location {
         const Iter = t: {
             const T = @TypeOf(iter);
@@ -121,4 +123,17 @@ pub const DiagnosticList = struct {
     pub fn items(self: *const DiagnosticList) []const Diagnostic {
         return self.list.items;
     }
+
+    /// Returns true if there are any diagnostics for the given
+    /// location type.
+    pub fn containsLocation(
+        self: *const DiagnosticList,
+        location: Location.Key,
+    ) bool {
+        for (self.list.items) |diag| {
+            if (diag.location == location) return true;
+        }
+
+        return false;
+    }
 };