Extract 'printLocation' & 'printSourceLocation' functions (#1984)

Context: facebook/relay#2752 (comment)

src/error/GraphQLError.js

@@ -1,10 +1,10 @@
 // @flow strict
 
 import isObjectLike from '../jsutils/isObjectLike';
-import { printError } from './printError';
 import { type ASTNode } from '../language/ast';
 import { type Source } from '../language/source';
 import { type SourceLocation, getLocation } from '../language/location';
+import { printLocation, printSourceLocation } from '../language/printLocation';
 
 /**
  * A GraphQLError describes an Error found during the parse, validate, or
@@ -217,3 +217,25 @@ export function GraphQLError( // eslint-disable-line no-redeclare
     },
   },
 });
+
+/**
+ * Prints a GraphQLError to a string, representing useful location information
+ * about the error's position in the source.
+ */
+export function printError(error: GraphQLError): string {
+  let output = error.message;
+
+  if (error.nodes) {
+    for (const node of error.nodes) {
+      if (node.loc) {
+        output += '\n\n' + printLocation(node.loc);
+      }
+    }
+  } else if (error.source && error.locations) {
+    for (const location of error.locations) {
+      output += '\n\n' + printSourceLocation(error.source, location);
+    }
+  }
+
+  return output;
+}

src/error/__tests__/GraphQLError-test.js

@@ -5,7 +5,14 @@ import { describe, it } from 'mocha';
 
 import dedent from '../../jsutils/dedent';
 import invariant from '../../jsutils/invariant';
-import { Kind, parse, Source, GraphQLError, formatError } from '../../';
+import {
+  Kind,
+  parse,
+  Source,
+  GraphQLError,
+  printError,
+  formatError,
+} from '../../';
 
 const source = new Source(dedent`
   {
@@ -155,3 +162,71 @@ describe('GraphQLError', () => {
     });
   });
 });
+
+describe('printError', () => {
+  it('prints an error without location', () => {
+    const error = new GraphQLError('Error without location');
+    expect(printError(error)).to.equal('Error without location');
+  });
+
+  it('prints an error using node without location', () => {
+    const error = new GraphQLError(
+      'Error attached to node without location',
+      parse('{ foo }', { noLocation: true }),
+    );
+    expect(printError(error)).to.equal(
+      'Error attached to node without location',
+    );
+  });
+
+  it('prints an error with nodes from different sources', () => {
+    const docA = parse(
+      new Source(
+        dedent`
+          type Foo {
+            field: String
+          }
+        `,
+        'SourceA',
+      ),
+    );
+    const opA = docA.definitions[0];
+    invariant(opA && opA.kind === Kind.OBJECT_TYPE_DEFINITION && opA.fields);
+    const fieldA = opA.fields[0];
+
+    const docB = parse(
+      new Source(
+        dedent`
+          type Foo {
+            field: Int
+          }
+        `,
+        'SourceB',
+      ),
+    );
+    const opB = docB.definitions[0];
+    invariant(opB && opB.kind === Kind.OBJECT_TYPE_DEFINITION && opB.fields);
+    const fieldB = opB.fields[0];
+
+    const error = new GraphQLError('Example error with two nodes', [
+      fieldA.type,
+      fieldB.type,
+    ]);
+
+    expect(printError(error) + '\n').to.equal(dedent`
+      Example error with two nodes
+
+      SourceA:2:10
+      1: type Foo {
+      2:   field: String
+                  ^
+      3: }
+
+      SourceB:2:10
+      1: type Foo {
+      2:   field: Int
+                  ^
+      3: }
+    `);
+  });
+});

src/error/index.js

@@ -1,12 +1,10 @@
 // @flow strict
 
-export { GraphQLError } from './GraphQLError';
+export { GraphQLError, printError } from './GraphQLError';
 
 export { syntaxError } from './syntaxError';
 
 export { locatedError } from './locatedError';
 
-export { printError } from './printError';
-
 export { formatError } from './formatError';
 export type { GraphQLFormattedError } from './formatError';

src/index.js

@@ -174,6 +174,9 @@ export type {
 export {
   Source,
   getLocation,
+  // Print source location
+  printLocation,
+  printSourceLocation,
   // Lex
   createLexer,
   TokenKind,

src/language/__tests__/printLocation-test.js

@@ -0,0 +1,37 @@
+// @flow strict
+
+import { expect } from 'chai';
+import { describe, it } from 'mocha';
+
+import dedent from '../../jsutils/dedent';
+import { Source } from '../../language';
+import { printSourceLocation } from '../printLocation';
+
+describe('printLocation', () => {
+  it('prints single digit line number with no padding', () => {
+    const result = printSourceLocation(
+      new Source('*', 'Test', { line: 9, column: 1 }),
+      { line: 1, column: 1 },
+    );
+
+    expect(result + '\n').to.equal(dedent`
+      Test:9:1
+      9: *
+         ^
+    `);
+  });
+
+  it('prints an line numbers with correct padding', () => {
+    const result = printSourceLocation(
+      new Source('*\n', 'Test', { line: 9, column: 1 }),
+      { line: 1, column: 1 },
+    );
+
+    expect(result + '\n').to.equal(dedent`
+      Test:9:1
+       9: *
+          ^
+      10: 
+    `);
+  });
+});

src/language/index.js

@@ -5,6 +5,8 @@ export { Source } from './source';
 export { getLocation } from './location';
 export type { SourceLocation } from './location';
 
+export { printLocation, printSourceLocation } from './printLocation';
+
 export { Kind } from './kinds';
 export type { KindEnum } from './kinds';
 

src/error/printError.js → src/language/printLocation.js

@@ -1,54 +1,35 @@
 // @flow strict
 
-import { type SourceLocation, getLocation } from '../language/location';
 import { type Source } from '../language/source';
-import { type GraphQLError } from './GraphQLError';
+import { type Location } from '../language/ast';
+import { type SourceLocation, getLocation } from '../language/location';
 
 /**
- * Prints a GraphQLError to a string, representing useful location information
- * about the error's position in the source.
+ * Render a helpful description of the location in the GraphQL Source document.
  */
-export function printError(error: GraphQLError): string {
-  const printedLocations = [];
-  if (error.nodes) {
-    for (const node of error.nodes) {
-      if (node.loc) {
-        printedLocations.push(
-          highlightSourceAtLocation(
-            node.loc.source,
-            getLocation(node.loc.source, node.loc.start),
-          ),
-        );
-      }
-    }
-  } else if (error.source && error.locations) {
-    const source = error.source;
-    for (const location of error.locations) {
-      printedLocations.push(highlightSourceAtLocation(source, location));
-    }
-  }
-  return printedLocations.length === 0
-    ? error.message
-    : [error.message, ...printedLocations].join('\n\n');
+export function printLocation(location: Location): string {
+  return printSourceLocation(
+    location.source,
+    getLocation(location.source, location.start),
+  );
 }
 
 /**
- * Render a helpful description of the location of the error in the GraphQL
- * Source document.
+ * Render a helpful description of the location in the GraphQL Source document.
  */
-function highlightSourceAtLocation(
+export function printSourceLocation(
   source: Source,
-  location: SourceLocation,
+  sourceLocation: SourceLocation,
 ): string {
   const firstLineColumnOffset = source.locationOffset.column - 1;
   const body = whitespace(firstLineColumnOffset) + source.body;
 
-  const lineIndex = location.line - 1;
+  const lineIndex = sourceLocation.line - 1;
   const lineOffset = source.locationOffset.line - 1;
-  const lineNum = location.line + lineOffset;
+  const lineNum = sourceLocation.line + lineOffset;
 
-  const columnOffset = location.line === 1 ? firstLineColumnOffset : 0;
-  const columnNum = location.column + columnOffset;
+  const columnOffset = sourceLocation.line === 1 ? firstLineColumnOffset : 0;
+  const columnNum = sourceLocation.column + columnOffset;
 
   const lines = body.split(/\r\n|[\n\r]/g);
   return (