Protect SwitchCase statements from ASI (#2008)

* Add no-semi test with SequenceExpression

Adapted from https://github.com/prettier/prettier/issues/2006

* Protect SequenceExpressions from ASI

Fixes https://github.com/prettier/prettier/issues/2006

* Add test for ASI protection of SequenceExpression outside SwitchCase

See https://github.com/prettier/prettier/pull/2008#issuecomment-306614217

* Revert "Protect SequenceExpressions from ASI"

This reverts commit ca644fad8072c90a977ad8a2f29674bc72f679e8.

* Protect SwitchCase statements from ASI

See https://github.com/prettier/prettier/pull/2008#issuecomment-306614217

Fixes https://github.com/prettier/prettier/issues/2006

src/printer.js

@@ -1488,7 +1488,15 @@ function genericPrintNoParens(path, options, print, args) {
                 const shouldAddLine =
                   i !== n.consequent.length - 1 &&
                   util.isNextLineEmpty(options.originalText, p.getValue());
-                return concat([print(p), shouldAddLine ? hardline : ""]);
+                const printed = concat([
+                  print(p),
+                  shouldAddLine ? hardline : ""
+                ]);
+                // in no-semi mode, prepend statement with semicolon if it might break ASI
+                if (!options.semi && stmtNeedsASIProtection(p)) {
+                  return concat([";", printed]);
+                }
+                return printed;
               })
               .filter(e => e !== null)
           );

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

@@ -81,6 +81,69 @@ x
 
 `;
 
+exports[`issue2006.js 1`] = `
+switch (n) {
+  case 11:
+    var c = a.e;
+    (i.a += Ga(c.e)), F(i, c.i, 0);
+}
+
+var c = a.e;
+(i.a += Ga(c.e)), F(i, c.i, 0);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+switch (n) {
+  case 11:
+    var c = a.e;
+    (i.a += Ga(c.e)), F(i, c.i, 0);
+}
+
+var c = a.e;
+(i.a += Ga(c.e)), F(i, c.i, 0);
+
+`;
+
+exports[`issue2006.js 2`] = `
+switch (n) {
+  case 11:
+    var c = a.e;
+    (i.a += Ga(c.e)), F(i, c.i, 0);
+}
+
+var c = a.e;
+(i.a += Ga(c.e)), F(i, c.i, 0);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+switch (n) {
+  case 11:
+    var c = a.e
+    ;(i.a += Ga(c.e)), F(i, c.i, 0)
+}
+
+var c = a.e
+;(i.a += Ga(c.e)), F(i, c.i, 0)
+
+`;
+
+exports[`issue2006.js 3`] = `
+switch (n) {
+  case 11:
+    var c = a.e;
+    (i.a += Ga(c.e)), F(i, c.i, 0);
+}
+
+var c = a.e;
+(i.a += Ga(c.e)), F(i, c.i, 0);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+switch (n) {
+  case 11:
+    var c = a.e
+    ;(i.a += Ga(c.e)), F(i, c.i, 0)
+}
+
+var c = a.e
+;(i.a += Ga(c.e)), F(i, c.i, 0)
+
+`;
+
 exports[`no-semi.js 1`] = `
 
 // with preexisting semi

tests/no-semi/issue2006.js

@@ -0,0 +1,8 @@
+switch (n) {
+  case 11:
+    var c = a.e;
+    (i.a += Ga(c.e)), F(i, c.i, 0);
+}
+
+var c = a.e;
+(i.a += Ga(c.e)), F(i, c.i, 0);