Make print() break arguments over multiple lines (#2797)

Author: draperunner

src/language/__tests__/printer-test.js

@@ -79,6 +79,45 @@ describe('Printer: Query document', () => {
     `);
   });
 
+  it('keeps arguments on one line if line is short (<= 80 chars)', () => {
+    const printed = print(
+      parse('{trip(wheelchair:false arriveBy:false){dateTime}}'),
+    );
+
+    expect(printed).to.equal(
+      dedent`
+      {
+        trip(wheelchair: false, arriveBy: false) {
+          dateTime
+        }
+      }
+    `,
+    );
+  });
+
+  it('puts arguments on multiple lines if line is long (> 80 chars)', () => {
+    const printed = print(
+      parse(
+        '{trip(wheelchair:false arriveBy:false includePlannedCancellations:true transitDistanceReluctance:2000){dateTime}}',
+      ),
+    );
+
+    expect(printed).to.equal(
+      dedent`
+      {
+        trip(
+          wheelchair: false
+          arriveBy: false
+          includePlannedCancellations: true
+          transitDistanceReluctance: 2000
+        ) {
+          dateTime
+        }
+      }
+    `,
+    );
+  });
+
   it('Experimental: prints fragment with variable directives', () => {
     const queryASTWithVariableDirective = parse(
       'fragment Foo($foo: TestType @test) on TestType @testDirective { id }',
@@ -158,9 +197,13 @@ describe('Printer: Query document', () => {
       }
 
       fragment frag on Friend @onFragmentDefinition {
-        foo(size: $size, bar: $b, obj: {key: "value", block: """
-          block string uses \"""
-        """})
+        foo(
+          size: $size
+          bar: $b
+          obj: {key: "value", block: """
+            block string uses \"""
+          """}
+        )
       }
 
       {

src/language/printer.js

@@ -11,6 +11,8 @@ export function print(ast: ASTNode): string {
   return visit(ast, { leave: printDocASTReducer });
 }
 
+const MAX_LINE_LENGTH = 80;
+
 // TODO: provide better type coverage in future
 const printDocASTReducer: any = {
   Name: (node) => node.value,
@@ -41,15 +43,16 @@ const printDocASTReducer: any = {
     wrap(' ', join(directives, ' ')),
   SelectionSet: ({ selections }) => block(selections),
 
-  Field: ({ alias, name, arguments: args, directives, selectionSet }) =>
-    join(
-      [
-        wrap('', alias, ': ') + name + wrap('(', join(args, ', '), ')'),
-        join(directives, ' '),
-        selectionSet,
-      ],
-      ' ',
-    ),
+  Field: ({ alias, name, arguments: args, directives, selectionSet }) => {
+    const prefix = wrap('', alias, ': ') + name;
+    let argsLine = prefix + wrap('(', join(args, ', '), ')');
+
+    if (argsLine.length > MAX_LINE_LENGTH) {
+      argsLine = prefix + wrap('(\n', indent(join(args, '\n')), '\n)');
+    }
+
+    return join([argsLine, join(directives, ' '), selectionSet], ' ');
+  },
 
   Argument: ({ name, value }) => name + ': ' + value,