make gobuild failures more readable.

1. ar reports names of objects with duplicate text symbols.
2. gobuild only shows first line of error output for each failed command.
3. gobuild ignores files that begin with ascii non-alphanumeric non _.

; gobuild
$ 6g -I _obj gobuild.go
  gobuild.go:150: PackageImports: undefined
$ 6g -I _obj makefile.go
  makefile.go:102: ShellString: undefined
$ 6g -I _obj util.go
  util.go:114: syntax error near zzz
gobuild: stalemate
;

; gobuild
$ 6ar grc _obj/gobuild.a util.6 util1.6
  duplicate text symbol: util1.6 and util.6: gobuild·Build
$ 6g -I _obj gobuild.go
  gobuild.go:150: PackageImports: undefined
$ 6g -I _obj makefile.go
  makefile.go:102: ShellString: undefined
gobuild: stalemate
;

R=r
DELTA=95  (49 added, 9 deleted, 37 changed)
OCL=29625
CL=29640

3 files changed, 76 insertions, 36 deletions

diff --git a/src/cmd/ar/ar.c b/src/cmd/ar/ar.c
index 733c4b5c8..35a3eeccd 100644
--- a/src/cmd/ar/ar.c
+++ b/src/cmd/ar/ar.c
@@ -58,6 +58,7 @@
 typedef struct	Arsymref
 {
 	char	*name;
+	char *file;
 	int	type;
 	int	len;
 	vlong	offset;
@@ -87,6 +88,7 @@ typedef	struct Arfile		/* Temp file control block - one per tempfile */
 typedef struct Hashchain
 {
 	char	*name;
+	char *file;
 	struct Hashchain *next;
 } Hashchain;
 
@@ -148,7 +150,7 @@ void	arread(Biobuf*, Armember*, int);
 void	arstream(int, Arfile*);
 int	arwrite(int, Armember*);
 int	bamatch(char*, char*);
-int	duplicate(char*);
+int	duplicate(char*, char**);
 Armember *getdir(Biobuf*);
 void	getpkgdef(char**, int*);
 int	getspace(void);
@@ -743,6 +745,7 @@ objsym(Sym *s, void *p)
 	int n;
 	Arsymref *as;
 	Arfile *ap;
+	char *ofile;
 
 	if (s->type != 'T' &&  s->type != 'D')
 		return;
@@ -750,9 +753,10 @@ objsym(Sym *s, void *p)
 	as = armalloc(sizeof(Arsymref));
 	as->offset = ap->size;
 	as->name = arstrdup(s->name);
-	if(s->type == 'T' && duplicate(as->name)) {
+	as->file = arstrdup(file);
+	if(s->type == 'T' && duplicate(as->name, &ofile)) {
 		dupfound = 1;
-		fprint(2, "duplicate text symbol: %s\n", as->name);
+		fprint(2, "duplicate text symbol: %s and %s: %s\n", as->file, ofile, as->name);
 		free(as->name);
 		free(as);
 		return;
@@ -783,7 +787,7 @@ hashstr(char *name)
 }
 
 int
-duplicate(char *name)
+duplicate(char *name, char **ofile)
 {
 	Hashchain *p;
 	int h;
@@ -791,12 +795,16 @@ duplicate(char *name)
 	h = hashstr(name) % NHASH;
 
 	for(p = hash[h]; p; p = p->next)
-		if(strcmp(p->name, name) == 0)
+		if(strcmp(p->name, name) == 0) {
+			*ofile = p->file;
 			return 1;
+		}
 	p = armalloc(sizeof(Hashchain));
 	p->next = hash[h];
 	p->name = name;
+	p->file = file;
 	hash[h] = p;
+	*ofile = nil;
 	return 0;
 }
 
@@ -893,7 +901,7 @@ getdir(Biobuf *b)
 	while(*--cp==' ')
 		;
 	cp[1] = '\0';
-	file = name;
+	file = arstrdup(name);
 	bp->date = strtol(bp->hdr.date, 0, 0);
 	bp->size = strtol(bp->hdr.size, 0, 0);
 	return bp;
@@ -1487,7 +1495,6 @@ loadpkgdata(char *data, int len)
 	char *p, *ep, *prefix, *name, *def;
 	Import *x;
 
-	file = arstrdup(file);
 	p = data;
 	ep = data + len;
 	while(parsepkgdata(&p, ep, &export, &prefix, &name, &def) > 0) {
diff --git a/src/cmd/gobuild/gobuild.go b/src/cmd/gobuild/gobuild.go
index 0db9bca04..c84c7e927 100644
--- a/src/cmd/gobuild/gobuild.go
+++ b/src/cmd/gobuild/gobuild.go
@@ -14,6 +14,8 @@ import (
 	"sort";
 	"strings";
 	"template";
+	"unicode";
+	"utf8";
 )
 
 type Pkg struct
@@ -148,9 +150,16 @@ func ScanFiles(filenames []string) *Info {
 		f := new(File);
 		f.Name = filename;
 		if path.Ext(filename) == ".go" {
+			rune, _ := utf8.DecodeRuneInString(filename);
+			if rune != '_' && !unicode.IsLetter(rune) && !unicode.IsDecimalDigit(rune) {
+				// Ignore files with funny leading letters,
+				// to avoid editor files like .foo.go and ~foo.go.
+				continue;
+			}
+
 			pkgname, imp, err := PackageImports(filename);
 			if err != nil {
-				fatal("parsing", filename, err.String());
+				fatal("parsing %s: %s", filename, err);
 			}
 			if pkgname == "main" {
 				continue;
@@ -182,7 +191,7 @@ func ScanFiles(filenames []string) *Info {
 			// non-Go file: fill in package name.
 			// Must only be a single package in this directory.
 			if len(z.Pkgmap) != 1 {
-				fatal("cannot determine package for ", f.Name);
+				fatal("cannot determine package for %s", f.Name);
 			}
 			f.Pkg = pkg;
 		}
@@ -240,7 +249,7 @@ func (z *Info) Build() {
 		fail = fail[0:0];
 		success = success[0:0];
 		for _, f := range pending {
-			if !Build(Compiler(f.Name), f.Name, false) {
+			if !Build(Compiler(f.Name), f.Name, 0) {
 				PushFile(&fail, f);
 			} else {
 				if *verbose {
@@ -252,7 +261,7 @@ func (z *Info) Build() {
 		if len(success) == 0 {
 			// Nothing ran; give up.
 			for _, f := range fail {
-				Build(Compiler(f.Name), f.Name, true);
+				Build(Compiler(f.Name), f.Name, ShowErrors | ForceDisplay);
 			}
 			fatal("stalemate");
 		}
@@ -310,7 +319,7 @@ func Main() {
 		var err os.Error;
 		filenames, err= SourceFiles(".");
 		if err != nil {
-			fatal("reading .: ", err.String());
+			fatal("reading .: %s", err.String());
 		}
 	}
 
@@ -319,11 +328,11 @@ func Main() {
 	if *writeMakefile {
 		t, err := template.Parse(makefileTemplate, makefileMap);
 		if err != nil {
-			fatal("template.Parse: ", err.String());
+			fatal("template.Parse: %s", err.String());
 		}
 		err = t.Execute(state, os.Stdout);
 		if err != nil {
-			fatal("template.Expand: ", err.String());
+			fatal("template.Expand: %s", err.String());
 		}
 	}
 }
diff --git a/src/cmd/gobuild/util.go b/src/cmd/gobuild/util.go
index 462d2dc95..e7b3c7789 100644
--- a/src/cmd/gobuild/util.go
+++ b/src/cmd/gobuild/util.go
@@ -6,8 +6,10 @@
 package gobuild
 
 import (
+	"bufio";
 	"exec";
 	"fmt";
+	"io";
 	"go/ast";
 	"go/parser";
 	"os";
@@ -17,6 +19,11 @@ import (
 	"strings";
 )
 
+const (
+	ShowErrors = 1<<iota;
+	ForceDisplay;
+)
+
 var (
 	theChar string;
 	goarch string;
@@ -32,8 +39,8 @@ var theChars = map[string] string {
 
 const ObjDir = "_obj"
 
-func fatal(args ...) {
-	fmt.Fprintf(os.Stderr, "gobuild: %s\n", fmt.Sprint(args));
+func fatal(format string, args ...) {
+	fmt.Fprintf(os.Stderr, "gobuild: %s\n", fmt.Sprintf(format, args));
 	os.Exit(1);
 }
 
@@ -45,7 +52,7 @@ func init() {
 	var ok bool;
 	theChar, ok = theChars[goarch];
 	if !ok {
-		fatal("unknown $GOARCH: ", goarch);
+		fatal("unknown $GOARCH: %s", goarch);
 	}
 
 	var binaries = []string{
@@ -58,7 +65,7 @@ func init() {
 	for i, v := range binaries {
 		var s string;
 		if s, err = exec.LookPath(v); err != nil {
-			fatal("cannot find binary ", v);
+			fatal("cannot find binary %s", v);
 		}
 		bin[v] = s;
 	}
@@ -79,38 +86,55 @@ func PushString(v *[]string, p string) {
 }
 
 
-func run(argv []string, display bool) (ok bool) {
+func run(argv []string, flag int) (ok bool) {
 	argv0 := bin[argv[0]];
-	output := exec.DevNull;
-	if display {
-		output = exec.PassThrough;
+	null, err := os.Open("/dev/null", os.O_RDWR, 0);
+	if err != nil {
+		fatal("open /dev/null: %s", err);
 	}
-	p, err1 := exec.Run(argv0, argv, os.Environ(), exec.DevNull, output, output);
-	if err1 != nil {
-		return false;
+	defer null.Close();
+	r, w, err := os.Pipe();
+	if err != nil {
+		fatal("pipe: %s", err);
 	}
-	w, err2 := p.Wait(0);
-	if err2 != nil {
+	pid, err := os.ForkExec(argv0, argv, os.Environ(), "", []*os.File{null, w, w});
+	defer r.Close();
+	w.Close();
+	if err != nil {
 		return false;
 	}
-	return w.Exited() && w.ExitStatus() == 0;
-}
 
-func Build(cmd []string, file string, display bool) (ok bool) {
-	if display {
+	// Read the first line of output, if any.  Discard the rest.
+	// If there is output and ShowErrors is set, show it,
+	// preceded by a shell command line.
+	// If ForceDisplay is set, we show the command even
+	// if there's no output; this gets set if we're just trying
+	// to keep the user informed.
+	b := bufio.NewReader(r);
+	line, err := b.ReadLineString('\n', true);
+	if flag & ShowErrors != 0 && line != "" || flag & ForceDisplay != 0 {
 		fmt.Fprint(os.Stderr, "$ ");
-		for i, s := range cmd {
+		for i, s := range argv {
 			fmt.Fprint(os.Stderr, s, " ");
 		}
-		fmt.Fprint(os.Stderr, file, "\n");
+		fmt.Fprint(os.Stderr, "\n");
+		fmt.Fprint(os.Stderr, "  ", line);
+		io.Copy(r, null);	// don't let process block on pipe
+	}
+	waitmsg, err := os.Wait(pid, 0);
+	if err != nil {
+		return false;
 	}
+	return waitmsg.Exited() && waitmsg.ExitStatus() == 0;
+}
 
+func Build(cmd []string, file string, flag int) (ok bool) {
 	var argv []string;
 	for i, c := range cmd {
 		PushString(&argv, c);
 	}
 	PushString(&argv, file);
-	return run(argv, display);
+	return run(argv, flag);
 }
 
 func Archive(pkg string, files []string) {
@@ -118,7 +142,7 @@ func Archive(pkg string, files []string) {
 	for i, file := range files {
 		PushString(&argv, file);
 	}
-	if !run(argv, true) {
+	if !run(argv, ShowErrors) {
 		fatal("archive failed");
 	}
 }
@@ -132,7 +156,7 @@ func Compiler(file string) []string {
 	case strings.HasSuffix(file, ".s"):
 		return []string{ theChar + "a" };
 	}
-	fatal("don't know how to compile ", file);
+	fatal("don't know how to compile %s", file);
 	return nil;
 }