augment corpus digraph logic to intake a vec of TextSource

Reviewed By: tyao1

Differential Revision: D52217455

fbshipit-source-id: 7ee4990c8b63c17588d87f6bda1db27d0482a2d0

Author: monicatang

compiler/crates/common/src/text_source.rs

@@ -71,6 +71,10 @@ impl TextSource {
         Range::new(start_position, end_position)
     }
 
+    /**
+     * Converts span, which is the relative indices of characters within this text source,
+     * into the equivalent line and character number range.
+     */
     pub fn to_span_range(&self, span: Span) -> lsp_types::Range {
         let start = span.start as usize;
         let end = span.end as usize;