[WIP] no-semi comments (#1257)

It doesn't yet work but I think it's close

src/comments.js

@@ -891,7 +891,7 @@ function printDanglingComments(path, options, sameIndent) {
   return indent(concat([hardline, join(hardline, parts)]));
 }
 
-function printComments(path, print, options) {
+function printComments(path, print, options, needsSemi) {
   var value = path.getValue();
   var parent = path.getParentNode();
   var printed = print(path);
@@ -902,7 +902,7 @@ function printComments(path, print, options) {
   }
 
   var leadingParts = [];
-  var trailingParts = [printed];
+  var trailingParts = [needsSemi ? ";" : "", printed];
 
   path.each(function(commentPath) {
     var comment = commentPath.getValue();

src/printer.js

@@ -2006,10 +2006,20 @@ function printStatementSequence(path, options, print) {
 
     // in no-semi mode, prepend statement with semicolon if it might break ASI
     if (!options.semi && !isClass && stmtNeedsASIProtection(stmtPath)) {
-      parts.push(";");
+      if (
+        stmt.comments &&
+        stmt.comments.some(comment => comment.leading)
+      ) {
+        // Note: stmtNeedsASIProtection requires stmtPath to already be printed
+        // as it reads needsParens which is mutated on the instance
+        parts.push(print(stmtPath, { needsSemi: true }));
+      } else {
+        parts.push(";", stmtPrinted);
+      }
+    } else {
+      parts.push(stmtPrinted);
     }
 
-    parts.push(stmtPrinted);
 
     if (!options.semi && isClass) {
       if (classPropMayCauseASIProblems(stmtPath)) {
@@ -3572,7 +3582,8 @@ function printAstToDoc(ast, options) {
     return comments.printComments(
       path,
       p => genericPrint(p, options, printGenerically, args),
-      options
+      options,
+      args && args.needsSemi
     );
   }
 

tests/no-semi/__snapshots__/jsfmt.spec.js.snap

@@ -1,5 +1,86 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`comments.js 1`] = `
+let error = new Error(response.statusText);
+// comment
+(error: any).response = response
+
+x;
+
+/* comment */ (error: any).response = response
+
+x;
+
+(error: any).response = response; /* comment */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+let error = new Error(response.statusText);
+// comment
+(error: any).response = response;
+
+x;
+
+/* comment */ (error: any).response = response;
+
+x;
+
+(error: any).response = response; /* comment */
+
+`;
+
+exports[`comments.js 2`] = `
+let error = new Error(response.statusText);
+// comment
+(error: any).response = response
+
+x;
+
+/* comment */ (error: any).response = response
+
+x;
+
+(error: any).response = response; /* comment */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+let error = new Error(response.statusText)
+// comment
+;(error: any).response = response
+
+x
+
+/* comment */ ;(error: any).response = response
+
+x
+
+;(error: any).response = response /* comment */
+
+`;
+
+exports[`comments.js 3`] = `
+let error = new Error(response.statusText);
+// comment
+(error: any).response = response
+
+x;
+
+/* comment */ (error: any).response = response
+
+x;
+
+(error: any).response = response; /* comment */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+let error = new Error(response.statusText)
+// comment
+;(error: any).response = response
+
+x
+
+/* comment */ ;(error: any).response = response
+
+x
+
+;(error: any).response = response /* comment */
+
+`;
+
 exports[`no-semi.js 1`] = `
 
 // with preexisting semi
@@ -591,9 +672,9 @@ if (true) {
   ;(() => {})()
 }
 
-;// flow
+// flow
 
-(x: void)
+;(x: void)
 ;(y: void)
 
 // check statement clauses
@@ -913,9 +994,9 @@ if (true) {
   ;(() => {})()
 }
 
-;// flow
+// flow
 
-(x: void)
+;(x: void)
 ;(y: void)
 
 // check statement clauses

tests/no-semi/comments.js

@@ -0,0 +1,11 @@
+let error = new Error(response.statusText);
+// comment
+(error: any).response = response
+
+x;
+
+/* comment */ (error: any).response = response
+
+x;
+
+(error: any).response = response; /* comment */