Allow shape to propagate through AssignPieces.

CHANGELOG.md

@@ -2,6 +2,41 @@
 
 * Format null-aware elements.
 
+* Allow more code on the same line as a named argument or `=>` (#1536, #1545,
+  #1668, #1679).
+
+  ```dart
+  // Before:
+  function(
+    name:
+        (param, another) =>
+            veryLongBody,
+  );
+
+  function(
+    name:
+        (param) => another(
+          argument1,
+          argument2,
+          argument3,
+        ),
+  );
+
+  // After:
+  function(
+    name: (param, another) =>
+        veryLongBody,
+  );
+
+  function(
+    name: (param) => another(
+      argument1,
+      argument2,
+      argument3,
+    ),
+  );
+  ```
+
 * Avoid splitting chains containing only properties.
 
   ```dart

lib/src/piece/assign.dart

@@ -124,23 +124,29 @@ final class AssignPiece extends Piece {
 
   @override
   void format(CodeWriter writer, State state) {
-    writer.setShapeMode(ShapeMode.other);
-
-    // When splitting at the operator, both operands may split or not and
-    // will be indented if they do.
-    if (state == State.split) writer.pushIndent(Indent.expression);
-
-    writer.format(_left);
-    writer.splitIf(state == State.split);
-
     if (state == State.split) {
+      // When splitting at the operator, indent the operands.
+      writer.pushIndent(Indent.expression);
+
+      // Treat a split `=` as potentially headline-shaped if the LHS doesn't
+      // split. Allows:
+      //
+      //     variable = another =
+      //         'split at second "="';
+      writer.setShapeMode(ShapeMode.beforeHeadline);
+      writer.format(_left);
+      writer.setShapeMode(ShapeMode.afterHeadline);
+
+      writer.newline();
       writer.popIndent();
       writer.pushIndent(Indent.assignment);
+      writer.format(_right);
+      writer.popIndent();
+    } else {
+      writer.format(_left);
+      writer.space();
+      writer.format(_right);
     }
-
-    writer.format(_right);
-
-    if (state == State.split) writer.popIndent();
   }
 
   @override

lib/src/piece/chain.dart

@@ -202,6 +202,22 @@ final class ChainPiece extends Piece {
         writer.popIndent();
 
       case _blockFormatTrailingCall:
+        // Don't treat a cascade as block-shaped in the surrounding context
+        // even if it block splits. Prefer:
+        //
+        //     variable = target
+        //       ..cascade(argument);
+        //
+        // Over:
+        //
+        //     variable = target..cascade(
+        //       argument,
+        //     );
+        //
+        // Note how the former makes it clearer that `variable` will be assigned
+        // the value `target` and that the cascade is a secondary side-effect.
+        if (_isCascade) writer.setShapeMode(ShapeMode.other);
+
         writer.format(_target);
 
         for (var i = 0; i < _calls.length; i++) {

test/tall/expression/assignment.stmt

@@ -79,16 +79,15 @@ target
         .another
         .lastOneReallyLong =
     reallyLongValue;
->>> Don't block format through nested assignments.
+>>> Allow block formatting through nested assignments.
 outer = inner = [element1, element2, element3, element4];
 <<<
-outer =
-    inner = [
-      element1,
-      element2,
-      element3,
-      element4,
-    ];
+outer = inner = [
+  element1,
+  element2,
+  element3,
+  element4,
+];
 >>> Headline format unsplit target of call chain.
 variable = (tar + get).method().another().third();
 <<<

test/tall/invocation/cascade_mixed.stmt

@@ -40,4 +40,18 @@ object
 >>> Chain with index target.
 object..[index].method();
 <<<
-object..[index].method();
+object..[index].method();
+>>> Don't treat cascade as block-shaped in assignment.
+variable = target..method(argument1, argument2);
+<<<
+variable = target
+  ..method(argument1, argument2);
+>>> Don't treat cascade as block-shaped even if the argument list splits.
+variable = target..method(argument1, argument2, argument3);
+<<<
+variable = target
+  ..method(
+    argument1,
+    argument2,
+    argument3,
+  );

test/tall/invocation/named_argument.stmt

@@ -73,3 +73,20 @@ function(
         body;
       },
 );
+>>> Headline formatting for a split `=>` function.
+function(name: (param, another) => veryLongBody);
+<<<
+function(
+  name: (param, another) =>
+      veryLongBody,
+);
+>>> Block-like formatting of a `=>` body containing a function call.
+function(name: (param) => another(argument1, argument2, argument3));
+<<<
+function(
+  name: (param) => another(
+    argument1,
+    argument2,
+    argument3,
+  ),
+);

test/tall/regression/0000/0040.stmt

@@ -14,8 +14,9 @@
           "e"
         ]);
 <<<
-      var s = new Serialization()..addRuleFor(
-        Various,
-        constructor: "Foo",
-        constructorFields: ["d", "e"],
-      );
+      var s = new Serialization()
+        ..addRuleFor(
+          Various,
+          constructor: "Foo",
+          constructorFields: ["d", "e"],
+        );

test/tall/regression/0000/0056.stmt

@@ -1,5 +1,7 @@
 >>> (indent 8)
         _sources[uri] = src = new _MockSdkSource(uri, 'library dart.${uri.path};');
 <<<
-        _sources[uri] =
-            src = new _MockSdkSource(uri, 'library dart.${uri.path};');
+        _sources[uri] = src = new _MockSdkSource(
+          uri,
+          'library dart.${uri.path};',
+        );

test/tall/regression/0100/0158.unit

@@ -10,8 +10,10 @@ void foo() {
 void foo() {
   if (bar) {
     if (baz) {
-      _sources[uri] =
-          src = new _MockSdkSource(uri, 'library dart.${uri.path};');
+      _sources[uri] = src = new _MockSdkSource(
+        uri,
+        'library dart.${uri.path};',
+      );
     }
   }
 }

test/tall/regression/0200/0221.unit

@@ -13,10 +13,9 @@ class Foo {
   static Column column(Handler onSelection) =>
       (Column.defaultBuilder(videoMsg())
             ..id = 'VIDEO'
-            ..segment =
-                ((row) => row.segmentedStats
-                    .map((s) => s.get(Stats.SEGMENTATION))
-                    .toList())
+            ..segment = ((row) => row.segmentedStats
+                .map((s) => s.get(Stats.SEGMENTATION))
+                .toList())
             ..cell = new Cell(onSelection))
           .build();
 }

test/tall/regression/0500/0500.unit

@@ -28,19 +28,18 @@
       env.initialize(
         names[i],
         getter: (TopLevelBinding binding, ExprCont ek, ExprCont k) {
-          binding.getter =
-              (TopLevelBinding _, ExprCont ek0, ExprCont k0) => ek0(
-                "Reading static variable '${binding.name}' during its initialization",
-              );
+          binding
+              .getter = (TopLevelBinding _, ExprCont ek0, ExprCont k0) => ek0(
+            "Reading static variable '${binding.name}' during its initialization",
+          );
           initializers[i](env, ek, (v) {
-            binding.getter =
-                (TopLevelBinding _, ExprCont ek1, ExprCont k1) => k1(v);
+            binding.getter = (TopLevelBinding _, ExprCont ek1, ExprCont k1) =>
+                k1(v);
             return k(v);
           });
         },
-        setter:
-            (value, ExprCont ek, ExprCont k) =>
-                ek("NoSuchMethodError: method not found: '${names[i]}='"),
+        setter: (value, ExprCont ek, ExprCont k) =>
+            ek("NoSuchMethodError: method not found: '${names[i]}='"),
       );
     }
   };

test/tall/regression/0500/0591.unit

@@ -9,9 +9,11 @@ void fn81() {
 <<<
 void fn81() {
   // The number of characters in the `four` line is ...........................81
-  var list = (one.two().three()..four(
-    '_15___20___25___30___35___40___45___50___55___60___65___70___75___',
-  ))..six('zzzzzzzzzzzzzzzzzzzzzzzzzzzz');
+  var list =
+      (one.two().three()..four(
+          '_15___20___25___30___35___40___45___50___55___60___65___70___75___',
+        ))
+        ..six('zzzzzzzzzzzzzzzzzzzzzzzzzzzz');
   ;
 }
 >>>
@@ -25,9 +27,11 @@ void fn80() {
 <<<
 void fn80() {
   // The number of characters in the `four` line is ..........................80
-  var list = (one.two().three()..four(
-    '_15___20___25___30___35___40___45___50___55___60___65___70___75__',
-  ))..six('zzzzzzzzzzzzzzzzzzzzzzzzzzzz');
+  var list =
+      (one.two().three()..four(
+          '_15___20___25___30___35___40___45___50___55___60___65___70___75__',
+        ))
+        ..six('zzzzzzzzzzzzzzzzzzzzzzzzzzzz');
   ;
 }
 >>>
@@ -41,9 +45,11 @@ void fn79() {
 <<<
 void fn79() {
   // The number of characters in the `four` line is .........................79
-  var list = (one.two().three()..four(
-    '_15___20___25___30___35___40___45___50___55___60___65___70___75_',
-  ))..six('zzzzzzzzzzzzzzzzzzzzzzzzzzzz');
+  var list =
+      (one.two().three()..four(
+          '_15___20___25___30___35___40___45___50___55___60___65___70___75_',
+        ))
+        ..six('zzzzzzzzzzzzzzzzzzzzzzzzzzzz');
   ;
 }
 >>>
@@ -57,9 +63,11 @@ void fn78() {
 <<<
 void fn78() {
   // The number of characters in the `four` line is ........................78
-  var list = (one.two().three()..four(
-    '_15___20___25___30___35___40___45___50___55___60___65___70___75',
-  ))..six('zzzzzzzzzzzzzzzzzzzzzzzzzzzz');
+  var list =
+      (one.two().three()..four(
+          '_15___20___25___30___35___40___45___50___55___60___65___70___75',
+        ))
+        ..six('zzzzzzzzzzzzzzzzzzzzzzzzzzzz');
   ;
 }
 >>>
@@ -73,9 +81,11 @@ void fn77() {
 <<<
 void fn77() {
   // The number of characters in the `four` line is .......................77
-  var list = (one.two().three()..four(
-    '_15___20___25___30___35___40___45___50___55___60___65___70___7',
-  ))..six('zzzzzzzzzzzzzzzzzzzzzzzzzzzz');
+  var list =
+      (one.two().three()..four(
+          '_15___20___25___30___35___40___45___50___55___60___65___70___7',
+        ))
+        ..six('zzzzzzzzzzzzzzzzzzzzzzzzzzzz');
   ;
 }
 >>>
@@ -89,8 +99,10 @@ void fn76() {
 <<<
 void fn76() {
   // The number of characters in the `four` line is ......................76
-  var list = (one.two().three()..four(
-    '_15___20___25___30___35___40___45___50___55___60___65___70___',
-  ))..six('zzzzzzzzzzzzzzzzzzzzzzzzzzzz');
+  var list =
+      (one.two().three()..four(
+          '_15___20___25___30___35___40___45___50___55___60___65___70___',
+        ))
+        ..six('zzzzzzzzzzzzzzzzzzzzzzzzzzzz');
   ;
 }

test/tall/regression/0700/0731.stmt

@@ -73,9 +73,8 @@
 <<<
     return Observable(_databaseService.getChatEntries(event)).map((entryList) {
       entryList.forEach(
-        (entry) =>
-            entry.isFromCurrentUser =
-                (entry.userId == _userManager.currentUser.id),
+        (entry) => entry.isFromCurrentUser =
+            (entry.userId == _userManager.currentUser.id),
       );
       return entryList;
     });
@@ -95,9 +94,8 @@
     return Observable(_databaseService.getChatEntries(event))
         .map((entryList) {
           entryList.forEach(
-            (entry) =>
-                entry.isFromCurrentUser =
-                    (entry.userId == _userManager.currentUser.id),
+            (entry) => entry.isFromCurrentUser =
+                (entry.userId == _userManager.currentUser.id),
           );
           return entryList;
         })