Fix files with comments only (#813)

* Add new handleOnlyComments function.

* Update tests.

* Update test as the printer forces a trailing newline if there were any contents.

* Implement a different heuristic.

* Update tests.

* Add directives checking in handleOnlyComments function.

* Add directives checking in handleOnlyComments function (amend to retrigger CI).

* Remove duplicate.

src/comments.js

@@ -132,13 +132,15 @@ function attach(comments, ast, text, options) {
 
   var tiesToBreak = [];
 
-  comments.forEach(function(comment) {
+  comments.forEach((comment, i) => {
     decorateComment(ast, comment, text);
 
     const precedingNode = comment.precedingNode;
     const enclosingNode = comment.enclosingNode;
     const followingNode = comment.followingNode;
 
+    const isLastComment = comments.length - 1 === i;
+
     if (util.hasNewline(text, locStart(comment), { backwards: true })) {
       // If a comment exists on its own line, prefer a leading comment.
       // We also need to check if it's the first line of the file.
@@ -152,14 +154,15 @@ function attach(comments, ast, text, options) {
         handleMemberExpressionComments(enclosingNode, followingNode, comment) ||
         handleIfStatementComments(enclosingNode, followingNode, comment) ||
         handleTryStatementComments(enclosingNode, followingNode, comment) ||
-        handleImportSpecifierComments(enclosingNode, comment) ||
         handleClassComments(enclosingNode, comment) ||
+        handleImportSpecifierComments(enclosingNode, comment) ||
         handleUnionTypeComments(
           precedingNode,
           enclosingNode,
           followingNode,
           comment
-        )
+        ) ||
+        handleOnlyComments(enclosingNode, ast, comment, isLastComment)
       ) {
         // We're good
       } else if (followingNode) {
@@ -184,10 +187,11 @@ function attach(comments, ast, text, options) {
         ) ||
         handleImportSpecifierComments(enclosingNode, comment) ||
         handleTemplateLiteralComments(enclosingNode, comment) ||
-        handleCallExpressionComments(precedingNode, enclosingNode, comment) ||
         handleClassComments(enclosingNode, comment) ||
+        handleCallExpressionComments(precedingNode, enclosingNode, comment) ||
         handlePropertyComments(enclosingNode, comment) ||
-        handleExportNamedDeclarationComments(enclosingNode, comment)
+        handleExportNamedDeclarationComments(enclosingNode, comment) ||
+        handleOnlyComments(enclosingNode, ast, comment, isLastComment)
       ) {
         // We're good
       } else if (precedingNode) {
@@ -207,7 +211,8 @@ function attach(comments, ast, text, options) {
         handleIfStatementComments(enclosingNode, followingNode, comment) ||
         handleObjectProperty(enclosingNode, precedingNode, comment) ||
         handleTemplateLiteralComments(enclosingNode, comment) ||
-        handleFunctionDeclarationComments(enclosingNode, comment)
+        handleFunctionDeclarationComments(enclosingNode, comment) ||
+        handleOnlyComments(enclosingNode, ast, comment, isLastComment)
       ) {
         // We're good
       } else if (precedingNode && followingNode) {
@@ -584,6 +589,30 @@ function handleExportNamedDeclarationComments(enclosingNode, comment) {
   return false;
 }
 
+function handleOnlyComments(enclosingNode, ast, comment, isLastComment) {
+  // With Flow the enclosingNode is undefined so use the AST instead.
+  if (ast && ast.body && ast.body.length === 0) {
+    if (isLastComment) {
+      addDanglingComment(ast, comment);
+    } else {
+      addLeadingComment(ast, comment);
+    }
+    return true;
+  } else if (
+    enclosingNode && enclosingNode.type === 'Program' &&
+    enclosingNode.body.length === 0 && enclosingNode.directives &&
+    enclosingNode.directives.length === 0
+  ) {
+    if (isLastComment) {
+      addDanglingComment(enclosingNode, comment);
+    } else {
+      addLeadingComment(enclosingNode, comment);
+    }
+    return true;
+  }
+  return false;
+}
+
 function printComment(commentPath) {
   const comment = commentPath.getValue();
   comment.printed = true;

tests/comments/__snapshots__/jsfmt.spec.js.snap

@@ -44,12 +44,44 @@ exports[`blank.js 1`] = `
 // should still exist
 //
 // when printed.
+
+/**
+ * @typedef {DataDrivenMapping|ConstantMapping} Mapping
+ */
+/**
+ * @typedef {Object.<String, Mapping>} ConfigurationMapping
+ */
+
+/**
+ * @typedef {Function} D3Scale - a D3 scale
+ * @property {Function} ticks
+ * @property {Function} tickFormat
+ */
+// comment
+
+// comment
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // This file only
 // has comments. This comment
 // should still exist
 //
 // when printed.
+
+/**
+ * @typedef {DataDrivenMapping|ConstantMapping} Mapping
+ */
+/**
+ * @typedef {Object.<String, Mapping>} ConfigurationMapping
+ */
+
+/**
+ * @typedef {Function} D3Scale - a D3 scale
+ * @property {Function} ticks
+ * @property {Function} tickFormat
+ */
+// comment
+
+// comment
 "
 `;
 
@@ -59,12 +91,44 @@ exports[`blank.js 2`] = `
 // should still exist
 //
 // when printed.
+
+/**
+ * @typedef {DataDrivenMapping|ConstantMapping} Mapping
+ */
+/**
+ * @typedef {Object.<String, Mapping>} ConfigurationMapping
+ */
+
+/**
+ * @typedef {Function} D3Scale - a D3 scale
+ * @property {Function} ticks
+ * @property {Function} tickFormat
+ */
+// comment
+
+// comment
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // This file only
 // has comments. This comment
 // should still exist
 //
 // when printed.
+
+/**
+ * @typedef {DataDrivenMapping|ConstantMapping} Mapping
+ */
+/**
+ * @typedef {Object.<String, Mapping>} ConfigurationMapping
+ */
+
+/**
+ * @typedef {Function} D3Scale - a D3 scale
+ * @property {Function} ticks
+ * @property {Function} tickFormat
+ */
+// comment
+
+// comment
 "
 `;
 

tests/comments/blank.js

@@ -3,3 +3,19 @@
 // should still exist
 //
 // when printed.
+
+/**
+ * @typedef {DataDrivenMapping|ConstantMapping} Mapping
+ */
+/**
+ * @typedef {Object.<String, Mapping>} ConfigurationMapping
+ */
+
+/**
+ * @typedef {Function} D3Scale - a D3 scale
+ * @property {Function} ticks
+ * @property {Function} tickFormat
+ */
+// comment
+
+// comment

tests/flow/declare_export/__snapshots__/jsfmt.spec.js.snap

@@ -586,6 +586,7 @@ export default {
  * @providesModule ES6Default
  * @flow
  */
+
 /*
 export default {
   numberValue: 42,

tests/flow/es6modules/__snapshots__/jsfmt.spec.js.snap

@@ -686,6 +686,7 @@ export default {
  * @providesModule ES6Default
  * @flow
  */
+
 /*
 export default {
   numberValue: 42,