fix: Add ts-ignore to reassignment of generated function (#557)

packages/istanbul-lib-instrument/src/visitor.js

@@ -534,7 +534,8 @@ const globalTemplateVariable = template(`
         var global = GLOBAL_COVERAGE_SCOPE;
 `);
 // the template to insert at the top of the program.
-const coverageTemplate = template(`
+const coverageTemplate = template(
+    `
     function COVERAGE_FUNCTION () {
         var path = PATH;
         var hash = HASH;
@@ -547,13 +548,18 @@ const coverageTemplate = template(`
         }
 
         var actualCoverage = coverage[path];
-        COVERAGE_FUNCTION = function () {
-          return actualCoverage;
+        {
+            // @ts-ignore
+            COVERAGE_FUNCTION = function () {
+                return actualCoverage;
+            }
         }
 
         return actualCoverage;
     }
-`);
+`,
+    { preserveComments: true }
+);
 // the rewire plugin (and potentially other babel middleware)
 // may cause files to be instrumented twice, see:
 // https://github.com/istanbuljs/babel-plugin-istanbul/issues/94