Don't insert space into empty switches. (#1199)

Fixes #1198.

Author: stereotype441

lib/src/source_visitor.dart

@@ -2723,6 +2723,15 @@ class SourceVisitor extends ThrowingAstVisitor {
 
   @override
   void visitSwitchExpression(SwitchExpression node) {
+    if (node.cases.isEmptyBody(node.rightBracket)) {
+      // Don't allow splitting an empty switch expression.
+      _visitSwitchValue(node.switchKeyword, node.leftParenthesis,
+          node.expression, node.rightParenthesis);
+      token(node.leftBracket);
+      token(node.rightBracket);
+      return;
+    }
+
     // Start the rule for splitting between the cases before the value. That
     // way, if the value expression splits, the cases do too. Avoids:
     //
@@ -2735,12 +2744,10 @@ class SourceVisitor extends ThrowingAstVisitor {
         node.rightParenthesis);
 
     token(node.leftBracket);
-    builder = builder.startBlock(space: true);
+    builder = builder.startBlock(space: node.cases.isNotEmpty);
 
     visitCommaSeparatedNodes(node.cases, between: split);
 
-    // A switch with no cases isn't syntactically valid, but handle it
-    // gracefully instead of crashing.
     var hasTrailingComma =
         node.cases.isNotEmpty && node.cases.last.commaAfter != null;
     _endBody(node.rightBracket, forceSplit: hasTrailingComma);
@@ -2836,8 +2843,10 @@ class SourceVisitor extends ThrowingAstVisitor {
       }
     }
 
-    newline();
-    _endBody(node.rightBracket, forceSplit: true);
+    if (node.members.isNotEmpty) {
+      newline();
+    }
+    _endBody(node.rightBracket, forceSplit: node.members.isNotEmpty);
   }
 
   /// Visits the `switch (expr)` part of a switch statement or expression.

test/comments/switch.stmt

@@ -144,4 +144,86 @@ e = switch (n) {
   0 => zero, // comment
   1 => one, // comment
   2 => two // comment
-};
+};
+>>> line comment
+switch (e) {
+  // comment
+}
+<<<
+switch (e) {
+  // comment
+}
+>>> line comment on opening line
+switch (e) { // comment
+}
+<<<
+switch (e) {
+  // comment
+}
+>>> indented block comment
+switch (e) {
+  /* comment */
+}
+<<<
+switch (e) {
+  /* comment */
+}
+>>> block comment with trailing newline
+switch (e) {/* comment */
+}
+<<<
+switch (e) {
+  /* comment */
+}
+>>> block comment with leading newline
+switch (e) {
+  /* comment */}
+<<<
+switch (e) {
+  /* comment */
+}
+>>> inline block comment
+switch (e) {  /* comment */  }
+<<<
+switch (e) {/* comment */}
+>>> line comment
+e = switch (n) {
+  // comment
+};
+<<<
+e = switch (n) {
+  // comment
+};
+>>> line comment on opening line
+e = switch (n) { // comment
+};
+<<<
+e = switch (n) {
+  // comment
+};
+>>> indented block comment
+e = switch (n) {
+  /* comment */
+};
+<<<
+e = switch (n) {
+  /* comment */
+};
+>>> block comment with trailing newline
+e = switch (n) {/* comment */
+};
+<<<
+e = switch (n) {
+  /* comment */
+};
+>>> block comment with leading newline
+e = switch (n) {
+  /* comment */};
+<<<
+e = switch (n) {
+  /* comment */
+};
+>>> inline block comment
+e = switch (n) {  /* comment */  };
+<<<
+e = switch (n) {/* comment */};

test/regression/1100/1198.stmt

@@ -0,0 +1,31 @@
+40 columns                              |
+>>>
+switch (e) {}
+<<<
+switch (e) {}
+>>>
+switch ("a long string that must wrap") {}
+<<<
+switch (
+    "a long string that must wrap") {}
+>>>
+switch ([1,]) {}
+<<<
+switch ([
+  1,
+]) {}
+>>>
+e = switch (e) {};
+<<<
+e = switch (e) {};
+>>>
+e = switch ("a long string that must wrap") {};
+<<<
+e = switch (
+    "a long string that must wrap") {};
+>>>
+e = switch ([1,]) {};
+<<<
+e = switch ([
+  1,
+]) {};

test/whitespace/switch.stmt

@@ -289,7 +289,7 @@ switch (obj) {
   case 1 is! int:
     body;
 }
->>> empty switch expression (error but handle gracefully)
+>>> empty switch expression
 var x = switch(y) {};
 <<<
-var x = switch (y) {  };
+var x = switch (y) {};