Fix empty lines with comments between switch cases (#1709)

The function isPreviousLineEmpty comment doesn't skip comments (on purpose, see comment above that method :P) so the detection is messed up. Turns out, it's easier to just use isNextLineEmpty like everywhere else.

Fixes #1708

src/printer.js

@@ -1385,7 +1385,24 @@ function genericPrintNoParens(path, options, print, args) {
         path.call(print, "discriminant"),
         ") {",
         n.cases.length > 0
-          ? indent(concat([hardline, join(hardline, path.map(print, "cases"))]))
+          ? indent(
+              concat([
+                hardline,
+                join(
+                  hardline,
+                  path.map(casePath => {
+                    const caseNode = casePath.getValue();
+                    return concat([
+                      casePath.call(print),
+                      n.cases.indexOf(caseNode) !== n.cases.length - 1 &&
+                        util.isNextLineEmpty(options.originalText, caseNode)
+                        ? hardline
+                        : ""
+                    ]);
+                  }, "cases")
+                )
+              ])
+            )
           : "",
         hardline,
         "}"
@@ -1397,16 +1414,11 @@ function genericPrintNoParens(path, options, print, args) {
         parts.push("default:");
       }
 
-      const isFirstCase = path.getNode() === path.getParentNode().cases[0];
+      const consequent = n.consequent.filter(
+        node => node.type !== "EmptyStatement"
+      );
 
-      if (
-        !isFirstCase &&
-        util.isPreviousLineEmpty(options.originalText, path.getValue())
-      ) {
-        parts.unshift(hardline);
-      }
-
-      if (n.consequent.find(node => node.type !== "EmptyStatement")) {
+      if (consequent.length > 0) {
         const cons = path.call(consequentPath => {
           return join(
             hardline,
@@ -1424,10 +1436,6 @@ function genericPrintNoParens(path, options, print, args) {
           );
         }, "consequent");
 
-        const consequent = n.consequent.filter(
-          node => node.type !== "EmptyStatement"
-        );
-
         parts.push(
           consequent.length === 1 && consequent[0].type === "BlockStatement"
             ? concat([" ", cons])

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

@@ -1,5 +1,56 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`comments.js 1`] = `
+switch (true) {
+  case true:
+  // Good luck getting here
+
+  case false:
+}
+
+switch (true) {
+  case true:
+
+  // Good luck getting here
+  case false:
+}
+
+switch(x) {
+  case x: {
+  }
+
+  // other
+
+  case y: {
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+switch (true) {
+  case true:
+  // Good luck getting here
+
+  case false:
+}
+
+switch (true) {
+  case true:
+
+  // Good luck getting here
+  case false:
+}
+
+switch (x) {
+  case x: {
+  }
+
+  // other
+
+  case y: {
+  }
+}
+
+`;
+
 exports[`empty_lines.js 1`] = `
 switch (foo) {
   case "bar":

tests/switch/comments.js

@@ -0,0 +1,23 @@
+switch (true) {
+  case true:
+  // Good luck getting here
+
+  case false:
+}
+
+switch (true) {
+  case true:
+
+  // Good luck getting here
+  case false:
+}
+
+switch(x) {
+  case x: {
+  }
+
+  // other
+
+  case y: {
+  }
+}