Improvements to printing block strings

src/language/__tests__/printer-test.js

@@ -71,6 +71,37 @@ describe('Printer', () => {
     `);
   });
 
+  it('correctly prints single-line block strings with leading space', () => {
+    const mutationAstWithArtifacts = parse(
+      '{ field(arg: """    space-led value""") }'
+    );
+    expect(print(mutationAstWithArtifacts)).to.equal(dedent`
+      {
+        field(arg: """    space-led value""")
+      }
+    `);
+  });
+
+  it('correctly prints block strings with a first line indentation', () => {
+    const mutationAstWithArtifacts = parse(`
+      {
+        field(arg: """
+              first
+            line
+          indentation
+        """)
+      }
+    `);
+    expect(print(mutationAstWithArtifacts)).to.equal(dedent`
+      {
+        field(arg: """
+              first
+            line
+          indentation
+        """)
+      }
+    `);
+  });
 
   const kitchenSink = readFileSync(
     join(__dirname, '/kitchen-sink.graphql'),
@@ -128,7 +159,7 @@ describe('Printer', () => {
 
       fragment frag on Friend {
         foo(size: $size, bar: $b, obj: {key: "value", block: """
-        block string uses \"""
+          block string uses \"""
         """})
       }
 

src/language/printer.js

@@ -74,7 +74,7 @@ const printDocASTReducer = {
   FloatValue: ({ value }) => value,
   StringValue: ({ value, block: isBlockString }) =>
     isBlockString ?
-      `"""\n${value.replace(/"""/g, '\\"""')}\n"""` :
+      printBlockString(value) :
       JSON.stringify(value),
   BooleanValue: ({ value }) => JSON.stringify(value),
   NullValue: () => 'null',
@@ -204,3 +204,14 @@ function wrap(start, maybeString, end) {
 function indent(maybeString) {
   return maybeString && maybeString.replace(/\n/g, '\n  ');
 }
+
+/**
+ * Print a block string in the indented block form by adding a leading and
+ * trailing blank line. However, if a block string starts with whitespace and is
+ * a single-line, adding a leading blank line would strip that whitespace.
+ */
+function printBlockString(value) {
+  return (value[0] === ' ' || value[0] === '\t') && value.indexOf('\n') === -1 ?
+    `"""${value.replace(/"""/g, '\\"""')}"""` :
+    indent('"""\n' + value.replace(/"""/g, '\\"""')) + '\n"""';
+}