Always split switch expressions (#1537)

Always split switch expressions.

I figured that since other comma-delimited expression forms don't split
if they don't have to, switch expressions should be the same. But I
went and checked on a huge corpus and every single place where a switch
expression wasn't split was clearly much worse than splitting it would
be.

Fix #1529.

lib/src/front_end/ast_node_visitor.dart

@@ -1718,7 +1718,7 @@ class AstNodeVisitor extends ThrowingAstVisitor<void> with PieceFactory {
     }
 
     list.rightBracket(node.rightBracket);
-    pieces.add(list.build());
+    pieces.add(list.build(forceSplit: node.cases.isNotEmpty));
   }
 
   @override

lib/src/front_end/delimited_list_builder.dart

@@ -51,7 +51,7 @@ class DelimitedListBuilder {
 
   /// Creates the final [ListPiece] out of the added brackets, delimiters,
   /// elements, and style.
-  Piece build() {
+  Piece build({bool forceSplit = false}) {
     // To simplify the piece tree, if there are no elements, just return the
     // brackets concatenated together. We don't have to worry about comments
     // here since they would be in the [_elements] list if there were any.
@@ -66,7 +66,7 @@ class DelimitedListBuilder {
 
     var piece =
         ListPiece(_leftBracket, _elements, _blanksAfter, _rightBracket, _style);
-    if (_mustSplit) piece.pin(State.split);
+    if (_mustSplit || forceSplit) piece.pin(State.split);
     return piece;
   }
 

test/tall/expression/switch.stmt

@@ -3,21 +3,20 @@
 e = switch(y) {};
 <<<
 e = switch (y) {};
->>> All one line.
+>>> Always split cases even if they would fit.
 e = switch (c) { 0 => a, 1 => b };
 <<<
-e = switch (c) { 0 => a, 1 => b };
+e = switch (c) {
+  0 => a,
+  1 => b,
+};
 >>> One case per line.
 e = switch (c) { 0 => first, 1 => second };
 <<<
 e = switch (c) {
   0 => first,
   1 => second,
 };
->>> Remove trailing comma if cases fit on one line.
-e = switch (c) { 0 => a, 1 => b, };
-<<<
-e = switch (c) { 0 => a, 1 => b };
 >>> Split some cases at "=>" but not all.
 e = switch (c) {
   first => a,

test/tall/invocation/block_argument_multiple.stmt

@@ -137,8 +137,12 @@ function(before, switch (n) {
 function(switch (a) { 1 => 2 }, switch (b) { 1 => 2 });
 <<<
 function(
-  switch (a) { 1 => 2 },
-  switch (b) { 1 => 2 },
+  switch (a) {
+    1 => 2,
+  },
+  switch (b) {
+    1 => 2,
+  },
 );
 >>> Empty and non-empty switches.
 function(switch (a) {}, switch (b) { 1 => 2 }, switch (c) {});

test/tall/regression/1500/1529.stmt

@@ -0,0 +1,67 @@
+>>> (indent 4)
+    return switch (that) { Family() => that, $FamilyOverride() => that.from };
+<<<
+    return switch (that) {
+      Family() => that,
+      $FamilyOverride() => that.from,
+    };
+>>> (indent 6)
+      x = switch (event) {
+        ProviderDisposeEvent() => switch (event
+            .debugOrigin) { ProviderDisposeEvent e => [e.refenaId], _ => null },
+      };
+<<<
+      x = switch (event) {
+        ProviderDisposeEvent() => switch (event.debugOrigin) {
+          ProviderDisposeEvent e => [e.refenaId],
+          _ => null,
+        },
+      };
+>>> (indent 6)
+      x = switch (event) {
+        RebuildEvent() => switch (event
+            .debugOrigin) { BaseReduxAction a => a.refenaId, _ => null },
+        ActionDispatchedEvent() => switch (event
+            .debugOriginRef) { BaseReduxAction a => a.refenaId, _ => null },
+        MessageEvent() => switch (event
+            .origin) { BaseReduxAction a => a.refenaId, _ => null },
+      };
+<<<
+      x = switch (event) {
+        RebuildEvent() => switch (event.debugOrigin) {
+          BaseReduxAction a => a.refenaId,
+          _ => null,
+        },
+        ActionDispatchedEvent() => switch (event.debugOriginRef) {
+          BaseReduxAction a => a.refenaId,
+          _ => null,
+        },
+        MessageEvent() => switch (event.origin) {
+          BaseReduxAction a => a.refenaId,
+          _ => null,
+        },
+      };
+>>> (indent 2)
+  T? valueOrNull() => switch (this) { Data(:var value) => value, _ => null };
+<<<
+  T? valueOrNull() => switch (this) {
+    Data(:var value) => value,
+    _ => null,
+  };
+>>> (indent 2)
+  String transcription(Locale intl) => switch (intl
+      .languageCode) { 'zh' => zhCN(this), 'be' => be(this), _ => basic(this) };
+<<<
+  String transcription(Locale intl) => switch (intl.languageCode) {
+    'zh' => zhCN(this),
+    'be' => be(this),
+    _ => basic(this),
+  };
+>>> (indent 4)
+    return switch (x) { <= 1 => x, >= 3 => x - 4, _ => 2 - x };
+<<<
+    return switch (x) {
+      <= 1 => x,
+      >= 3 => x - 4,
+      _ => 2 - x,
+    };