printSchema: handle descriptions that are non-printable as block strings

Fixes #2577
Fixes #2589

src/language/__tests__/blockString-fuzz.ts

@@ -8,7 +8,7 @@ import { invariant } from '../../jsutils/invariant';
 
 import { Lexer } from '../lexer';
 import { Source } from '../source';
-import { printBlockString } from '../blockString';
+import { printBlockString, isPrintableAsBlockString } from '../blockString';
 
 function lexValue(str: string): string {
   const lexer = new Lexer(new Source(str));
@@ -35,6 +35,18 @@ function testPrintableBlockString(
   );
 }
 
+function testNonPrintableBlockString(testValue: string): void {
+  const blockString = printBlockString(testValue);
+  const printedValue = lexValue(blockString);
+  invariant(
+    testValue !== printedValue,
+    dedent`
+      Expected lexValue(${inspectStr(blockString)})
+        to not equal ${inspectStr(testValue)}
+    `,
+  );
+}
+
 describe('printBlockString', () => {
   it('correctly print random strings', () => {
     // Testing with length >7 is taking exponentially more time. However it is
@@ -43,18 +55,13 @@ describe('printBlockString', () => {
       allowedChars: ['\n', '\t', ' ', '"', 'a', '\\'],
       maxLength: 7,
     })) {
-      const testStr = '"""' + fuzzStr + '"""';
-
-      let testValue;
-      try {
-        testValue = lexValue(testStr);
-      } catch (e) {
-        continue; // skip invalid values
+      if (!isPrintableAsBlockString(fuzzStr)) {
+        testNonPrintableBlockString(fuzzStr);
+        continue;
       }
-      invariant(typeof testValue === 'string');
 
-      testPrintableBlockString(testValue);
-      testPrintableBlockString(testValue, { minimize: true });
+      testPrintableBlockString(fuzzStr);
+      testPrintableBlockString(fuzzStr, { minimize: true });
     }
   }).timeout(20000);
 });

src/language/__tests__/blockString-test.ts

@@ -1,7 +1,11 @@
 import { expect } from 'chai';
 import { describe, it } from 'mocha';
 
-import { dedentBlockStringLines, printBlockString } from '../blockString';
+import {
+  isPrintableAsBlockString,
+  dedentBlockStringLines,
+  printBlockString,
+} from '../blockString';
 
 function joinLines(...args: ReadonlyArray<string>) {
   return args.join('\n');
@@ -135,6 +139,69 @@ describe('dedentBlockStringLines', () => {
   });
 });
 
+describe('isPrintableAsBlockString', () => {
+  function expectPrintable(str: string) {
+    return expect(isPrintableAsBlockString(str)).to.equal(true);
+  }
+
+  function expectNonPrintable(str: string) {
+    return expect(isPrintableAsBlockString(str)).to.equal(false);
+  }
+
+  it('accepts valid strings', () => {
+    expectPrintable('');
+    expectPrintable(' a');
+    expectPrintable('\t"\n"');
+    expectNonPrintable('\t"\n \n\t"');
+  });
+
+  it('rejects strings with only whitespace', () => {
+    expectNonPrintable(' ');
+    expectNonPrintable('\t');
+    expectNonPrintable('\t ');
+    expectNonPrintable(' \t');
+  });
+
+  it('rejects strings with non-printable character', () => {
+    expectNonPrintable('\x00');
+    expectNonPrintable('a\x00b');
+  });
+
+  it('rejects strings with non-printable character', () => {
+    expectNonPrintable('\x00');
+    expectNonPrintable('a\x00b');
+  });
+
+  it('rejects strings with only empty lines', () => {
+    expectNonPrintable('\n');
+    expectNonPrintable('\n\n');
+    expectNonPrintable('\n\n\n');
+    expectNonPrintable(' \n  \n');
+    expectNonPrintable('\t\n\t\t\n');
+  });
+
+  it('rejects strings with carriage return', () => {
+    expectNonPrintable('\r');
+    expectNonPrintable('\n\r');
+    expectNonPrintable('\r\n');
+    expectNonPrintable('a\rb');
+  });
+
+  it('rejects strings with leading empty lines', () => {
+    expectNonPrintable('\na');
+    expectNonPrintable(' \na');
+    expectNonPrintable('\t\na');
+    expectNonPrintable('\n\na');
+  });
+
+  it('rejects strings with leading empty lines', () => {
+    expectNonPrintable('a\n');
+    expectNonPrintable('a\n ');
+    expectNonPrintable('a\n\t');
+    expectNonPrintable('a\n\n');
+  });
+});
+
 describe('printBlockString', () => {
   function expectBlockString(str: string) {
     return {

src/language/blockString.ts

@@ -48,6 +48,69 @@ function leadingWhitespace(str: string): number {
   return i;
 }
 
+/**
+ * @internal
+ */
+export function isPrintableAsBlockString(value: string): boolean {
+  if (value === '') {
+    return true; // empty string is printable
+  }
+
+  let isEmptyLine = true;
+  let hasIndent = false;
+  let hasCommonIndent = true;
+  let seenNonEmptyLine = false;
+
+  for (let i = 0; i < value.length; ++i) {
+    switch (value.codePointAt(i)) {
+      case 0x0000:
+      case 0x0001:
+      case 0x0002:
+      case 0x0003:
+      case 0x0004:
+      case 0x0005:
+      case 0x0006:
+      case 0x0007:
+      case 0x0008:
+      case 0x000b:
+      case 0x000c:
+      case 0x000e:
+      case 0x000f:
+        return false; // Has non-printable characters
+
+      case 0x000d: //  \r
+        return false; // Has \r or \r\n which will be replaced as \n
+
+      case 10: //  \n
+        if (isEmptyLine && !seenNonEmptyLine) {
+          return false; // Has leading new line
+        }
+        seenNonEmptyLine = true;
+
+        isEmptyLine = true;
+        hasIndent = false;
+        break;
+      case 9: //   \t
+      case 32: //  <space>
+        hasIndent ||= isEmptyLine;
+        break;
+      default:
+        hasCommonIndent &&= hasIndent;
+        isEmptyLine = false;
+    }
+  }
+
+  if (isEmptyLine) {
+    return false; // Has trailing empty lines
+  }
+
+  if (hasCommonIndent && seenNonEmptyLine) {
+    return false; // Has internal indent
+  }
+
+  return true;
+}
+
 /**
  * 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

src/utilities/__tests__/printSchema-test.ts

@@ -593,6 +593,20 @@ describe('Type System Printer', () => {
     `);
   });
 
+  it('Prints an description with only whitespace', () => {
+    const schema = buildSingleFieldSchema({
+      type: GraphQLString,
+      description: ' ',
+    });
+
+    expectPrintedSchema(schema).to.equal(dedent`
+      type Query {
+        " "
+        singleField: String
+      }
+    `);
+  });
+
   it('One-line prints a short description', () => {
     const schema = buildSingleFieldSchema({
       type: GraphQLString,

src/utilities/printSchema.ts

@@ -4,6 +4,7 @@ import type { Maybe } from '../jsutils/Maybe';
 
 import { Kind } from '../language/kinds';
 import { print } from '../language/printer';
+import { isPrintableAsBlockString } from '../language/blockString';
 
 import type { GraphQLSchema } from '../type/schema';
 import type { GraphQLDirective } from '../type/directives';
@@ -316,7 +317,7 @@ function printDescription(
   const blockString = print({
     kind: Kind.STRING,
     value: description,
-    block: true,
+    block: isPrintableAsBlockString(description),
   });
 
   const prefix =