perf: Replace most sticky regexs with pure parser combinators (#52)

Author: kitten

.changeset/red-turkeys-flash.md

@@ -0,0 +1,5 @@
+---
+'@0no-co/graphql.web': minor
+---
+
+Improve parser performance (up to ~25% higher ops/s) by rewriting part of the parsing that runs in tight loops. Previously, the purer parser combinators w/o regexs wouldn't have been as significant of an improvement, but they now clearly are

scripts/eslint-preset.js

@@ -69,10 +69,6 @@ module.exports = {
             selector: 'AssignmentExpression[operator="??="]',
             message: 'Nullish coalescing assignment (??=) is outside of specified browser support',
           },
-          {
-            selector: 'SequenceExpression',
-            message: 'Sequence expressions are to be avoided since they can be confusing',
-          },
           {
             selector: ':not(ForStatement) > VariableDeclaration[declarations.length>1]',
             message: 'Only one variable declarator per variable declaration is preferred',

scripts/rollup.config.mjs

@@ -142,10 +142,7 @@ const outputPlugins = [
       booleans_as_integers: false,
       keep_fnames: true,
       keep_fargs: true,
-      if_return: false,
       ie8: false,
-      sequences: false,
-      loops: false,
       conditionals: false,
       join_vars: false,
     },

src/__tests__/parser.test.ts

@@ -42,6 +42,11 @@ describe('parse', () => {
     expect(() => {
       return parse('{ ...on }');
     }).toThrow();
+    // But does accept "oN"
+    expect(parse('{ ...oN }')).toHaveProperty(
+      'definitions.0.selectionSet.selections.0.name.value',
+      'oN'
+    );
   });
 
   it('parses directives on fragment spread', () => {
@@ -123,6 +128,16 @@ describe('parse', () => {
     }).not.toThrow();
   });
 
+  it('throws on invalid operations', () => {
+    expect(() => {
+      return parse(`
+        invalid {
+          field
+        }
+      `);
+    }).toThrow();
+  });
+
   it('parses named mutation operations', () => {
     expect(() => {
       return parse(`
@@ -255,6 +270,7 @@ describe('parse', () => {
     expect(() => parse('{ ... on Test }')).toThrow();
     expect(() => parse('{ ... {} }')).toThrow();
     expect(() => parse('{ ... }')).toThrow();
+    expect(() => parse('{ . }')).toThrow();
 
     expect(parse('{ ... on Test { field } }')).toHaveProperty(
       'definitions.0.selectionSet.selections.0',
@@ -497,6 +513,19 @@ describe('parseValue', () => {
     expect(parseValue({ body: 'null' })).toEqual({ kind: Kind.NULL });
   });
 
+  it('parses scalars', () => {
+    expect(parseValue('null')).toEqual({ kind: Kind.NULL });
+    expect(parseValue('true')).toEqual({ kind: Kind.BOOLEAN, value: true });
+    expect(parseValue('false')).toEqual({ kind: Kind.BOOLEAN, value: false });
+  });
+
+  it('parses scalars without optimistic failures', () => {
+    // for *n*ull, *f*alse, *t*rue
+    expect(parseValue('n')).toEqual({ kind: Kind.ENUM, value: 'n' });
+    expect(parseValue('f')).toEqual({ kind: Kind.ENUM, value: 'f' });
+    expect(parseValue('t')).toEqual({ kind: Kind.ENUM, value: 't' });
+  });
+
   it('parses list values', () => {
     const result = parseValue('[123 "abc"]');
     expect(result).toEqual({
@@ -542,6 +571,8 @@ describe('parseValue', () => {
       kind: Kind.FLOAT,
       value: '-1.2e+3',
     });
+
+    expect(() => parseValue('12e')).toThrow();
   });
 
   it('parses strings', () => {
@@ -580,6 +611,10 @@ describe('parseValue', () => {
       value: ' " ',
       block: false,
     });
+
+    expect(() => parseValue('"')).toThrow();
+    expect(() => parseValue('"\n')).toThrow();
+    expect(() => parseValue('"\r')).toThrow();
   });
 
   it('parses objects', () => {
@@ -674,6 +709,8 @@ describe('parseValue', () => {
       value: ' """ ',
       block: true,
     });
+
+    expect(() => parseValue('"""')).toThrow();
   });
 
   it('allows variables', () => {