Print trailing comma when last arg is arrow (#3428)

src/printer.js

@@ -3093,6 +3093,8 @@ function printArgumentsList(path, options, print) {
 
     const somePrintedArgumentsWillBreak = printedArguments.some(willBreak);
 
+    const maybeTrailingComma = shouldPrintComma(options, "all") ? "," : "";
+
     return concat([
       somePrintedArgumentsWillBreak ? breakParent : "",
       conditionalGroup(
@@ -3102,7 +3104,9 @@ function printArgumentsList(path, options, print) {
               indent(concat(["(", softline, concat(printedExpanded)])),
               concat(["(", concat(printedExpanded)])
             ),
-            somePrintedArgumentsWillBreak ? softline : "",
+            somePrintedArgumentsWillBreak
+              ? concat([ifBreak(maybeTrailingComma), softline])
+              : "",
             ")"
           ]),
           shouldGroupFirst
@@ -3124,7 +3128,7 @@ function printArgumentsList(path, options, print) {
             concat([
               "(",
               indent(concat([line, concat(printedArguments)])),
-              shouldPrintComma(options, "all") ? "," : "",
+              maybeTrailingComma,
               line,
               ")"
             ]),

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

@@ -129,6 +129,13 @@ a(
 );
 
 a('value', 'value2', a('long-nested-value', 'long-nested-value2', 'long-nested-value3'));
+
+a.b().c(
+  {
+    d,
+  },
+  () => {}
+);
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 const a = (param1, param2, param3) => {};
 
@@ -146,6 +153,13 @@ a(
   a("long-nested-value", "long-nested-value2", "long-nested-value3")
 );
 
+a.b().c(
+  {
+    d
+  },
+  () => {}
+);
+
 `;
 
 exports[`function-calls.js 2`] = `
@@ -160,6 +174,13 @@ a(
 );
 
 a('value', 'value2', a('long-nested-value', 'long-nested-value2', 'long-nested-value3'));
+
+a.b().c(
+  {
+    d,
+  },
+  () => {}
+);
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 const a = (param1, param2, param3) => {};
 
@@ -177,6 +198,13 @@ a(
   a("long-nested-value", "long-nested-value2", "long-nested-value3"),
 );
 
+a.b().c(
+  {
+    d,
+  },
+  () => {},
+);
+
 `;
 
 exports[`function-calls.js 3`] = `
@@ -191,6 +219,13 @@ a(
 );
 
 a('value', 'value2', a('long-nested-value', 'long-nested-value2', 'long-nested-value3'));
+
+a.b().c(
+  {
+    d,
+  },
+  () => {}
+);
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 const a = (param1, param2, param3) => {};
 
@@ -208,6 +243,13 @@ a(
   a("long-nested-value", "long-nested-value2", "long-nested-value3")
 );
 
+a.b().c(
+  {
+    d,
+  },
+  () => {}
+);
+
 `;
 
 exports[`jsx.js 1`] = `

tests/trailing_comma/function-calls.js

@@ -9,3 +9,10 @@ a(
 );
 
 a('value', 'value2', a('long-nested-value', 'long-nested-value2', 'long-nested-value3'));
+
+a.b().c(
+  {
+    d,
+  },
+  () => {}
+);