go/types: gotype to always report the same first error now

The old code may have reported different errors given an
erroneous package depending on the order in which files
were parsed concurrently. The new code always reports
errors in "file order", independent of processing order.

Also:
- simplified parsing code and internal concurrency control
- removed -seq flag which didn't really add useful functionality

Change-Id: I18e24e630f458f2bc107a7b83926ae761d63c334
Reviewed-on: https://go-review.googlesource.com/37655Reviewed-by: Alan Donovan <adonovan@google.com>

src/go/types/gotype.go

@@ -38,9 +38,7 @@ The flags are:
 	-c
 		compiler used for installed packages (gc, gccgo, or source); default: source
 
-Debugging flags:
-	-seq
-		parse sequentially, rather than in parallel
+Flags controlling additional output:
 	-ast
 		print AST (forces -seq)
 	-trace
@@ -82,6 +80,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"sync"
 	"time"
 )
 
@@ -93,7 +92,6 @@ var (
 	compiler  = flag.String("c", "source", "compiler used for installed packages (gc, gccgo, or source)")
 
 	// debugging support
-	sequential    = flag.Bool("seq", false, "parse sequentially, rather than in parallel")
 	printAST      = flag.Bool("ast", false, "print AST (forces -seq)")
 	printTrace    = flag.Bool("trace", false, "print parse trace (forces -seq)")
 	parseComments = flag.Bool("comments", false, "parse comments (ignored unless -ast or -trace is provided)")
@@ -102,6 +100,7 @@ var (
 var (
 	fset       = token.NewFileSet()
 	errorCount = 0
+	sequential = false
 	parserMode parser.Mode
 )
 
@@ -109,8 +108,12 @@ func initParserMode() {
 	if *allErrors {
 		parserMode |= parser.AllErrors
 	}
+	if *printAST {
+		sequential = true
+	}
 	if *printTrace {
 		parserMode |= parser.Trace
+		sequential = true
 	}
 	if *parseComments && (*printAST || *printTrace) {
 		parserMode |= parser.ParseComments
@@ -152,46 +155,36 @@ func parseStdin() (*ast.File, error) {
 	return parse("<standard input>", src)
 }
 
-func parseFiles(filenames []string) ([]*ast.File, error) {
+func parseFiles(dir string, filenames []string) ([]*ast.File, error) {
 	files := make([]*ast.File, len(filenames))
+	errors := make([]error, len(filenames))
 
-	if *sequential {
-		for i, filename := range filenames {
-			var err error
-			files[i], err = parse(filename, nil)
-			if err != nil {
-				return nil, err // leave unfinished goroutines hanging
-			}
-		}
-	} else {
-		type parseResult struct {
-			file *ast.File
-			err  error
-		}
-
-		out := make(chan parseResult)
-		for _, filename := range filenames {
-			go func(filename string) {
-				file, err := parse(filename, nil)
-				out <- parseResult{file, err}
-			}(filename)
+	var wg sync.WaitGroup
+	for i, filename := range filenames {
+		wg.Add(1)
+		go func(i int, filepath string) {
+			defer wg.Done()
+			files[i], errors[i] = parse(filepath, nil)
+		}(i, filepath.Join(dir, filename))
+		if sequential {
+			wg.Wait()
 		}
+	}
+	wg.Wait()
 
-		for i := range filenames {
-			res := <-out
-			if res.err != nil {
-				return nil, res.err // leave unfinished goroutines hanging
-			}
-			files[i] = res.file
+	// if there are errors, return the first one for deterministic results
+	for _, err := range errors {
+		if err != nil {
+			return nil, err
 		}
 	}
 
 	return files, nil
 }
 
-func parseDir(dirname string) ([]*ast.File, error) {
+func parseDir(dir string) ([]*ast.File, error) {
 	ctxt := build.Default
-	pkginfo, err := ctxt.ImportDir(dirname, 0)
+	pkginfo, err := ctxt.ImportDir(dir, 0)
 	if _, nogo := err.(*build.NoGoError); err != nil && !nogo {
 		return nil, err
 	}
@@ -200,12 +193,7 @@ func parseDir(dirname string) ([]*ast.File, error) {
 		filenames = append(filenames, pkginfo.TestGoFiles...)
 	}
 
-	// complete file names
-	for i, filename := range filenames {
-		filenames[i] = filepath.Join(dirname, filename)
-	}
-
-	return parseFiles(filenames)
+	return parseFiles(dir, filenames)
 }
 
 func getPkgFiles(args []string) ([]*ast.File, error) {
@@ -231,7 +219,7 @@ func getPkgFiles(args []string) ([]*ast.File, error) {
 	}
 
 	// list of files
-	return parseFiles(args)
+	return parseFiles("", args)
 }
 
 func checkPkgFiles(files []*ast.File) {
@@ -282,9 +270,6 @@ func printStats(d time.Duration) {
 func main() {
 	flag.Usage = usage
 	flag.Parse()
-	if *printAST || *printTrace {
-		*sequential = true
-	}
 	initParserMode()
 
 	start := time.Now()