Create checkers in parallel, fix race on parents (#775)

Co-authored-by: auvred <aauvred@gmail.com>
Co-authored-by: Anders Hejlsberg <andersh@microsoft.com>

Author: 3 people

internal/checker/checker.go

@@ -824,6 +824,8 @@ type Checker struct {
 }
 
 func NewChecker(program Program) *Checker {
+	program.BindSourceFiles()
+
 	c := &Checker{}
 	c.id = nextCheckerID.Add(1)
 	c.program = program
@@ -1198,7 +1200,6 @@ func (c *Checker) initializeIterationResolvers() {
 }
 
 func (c *Checker) initializeChecker() {
-	c.program.BindSourceFiles()
 	// Initialize global symbol table
 	augmentations := make([][]*ast.Node, 0, len(c.files))
 	for _, file := range c.files {
@@ -13214,7 +13215,9 @@ func (c *Checker) mergeSymbolTable(target ast.SymbolTable, source ast.SymbolTabl
 			// When merging the module augmentation into a.ts, the symbol for `A` will itself be merged, so its parent
 			// should be the merged module symbol. But the symbol for `B` has only one declaration, so its parent should
 			// be the module augmentation symbol, which contains its only declaration.
-			merged.Parent = mergedParent
+			if merged.Flags&ast.SymbolFlagsTransient != 0 {
+				merged.Parent = mergedParent
+			}
 		}
 		target[id] = merged
 	}

internal/compiler/program.go

@@ -215,9 +215,13 @@ func (p *Program) CheckSourceFiles() {
 func (p *Program) createCheckers() {
 	p.checkersOnce.Do(func() {
 		p.checkers = make([]*checker.Checker, core.IfElse(p.programOptions.SingleThreaded, 1, 4))
+		wg := core.NewWorkGroup(p.programOptions.SingleThreaded)
 		for i := range p.checkers {
-			p.checkers[i] = checker.NewChecker(p)
+			wg.Queue(func() {
+				p.checkers[i] = checker.NewChecker(p)
+			})
 		}
+		wg.RunAndWait()
 		p.checkersByFile = make(map[*ast.SourceFile]*checker.Checker)
 		for i, file := range p.files {
 			p.checkersByFile[file] = p.checkers[i%len(p.checkers)]