go/parser: check import path restrictions

Replaces pending CL 5674097.
Thanks to ality@pbrane.org for spearheading
the effort.

R=rsc, r
CC=golang-dev
https://golang.org/cl/5683077

src/pkg/go/parser/parser.go

@@ -14,6 +14,9 @@ import (
 	"go/ast"
 	"go/scanner"
 	"go/token"
+	"strconv"
+	"strings"
+	"unicode"
 )
 
 // The parser structure holds the parser's internal state.
@@ -1913,6 +1916,17 @@ func (p *parser) parseStmt() (s ast.Stmt) {
 
 type parseSpecFunction func(p *parser, doc *ast.CommentGroup, iota int) ast.Spec
 
+func isValidImport(lit string) bool {
+	const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
+	s, _ := strconv.Unquote(lit) // go/scanner returns a legal string literal
+	for _, r := range s {
+		if !unicode.IsGraphic(r) || unicode.IsSpace(r) || strings.ContainsRune(illegalChars, r) {
+			return false
+		}
+	}
+	return s != ""
+}
+
 func parseImportSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
 	if p.trace {
 		defer un(trace(p, "ImportSpec"))
@@ -1929,6 +1943,9 @@ func parseImportSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
 
 	var path *ast.BasicLit
 	if p.tok == token.STRING {
+		if !isValidImport(p.lit) {
+			p.error(p.pos, "invalid import path: "+p.lit)
+		}
 		path = &ast.BasicLit{ValuePos: p.pos, Kind: p.tok, Value: p.lit}
 		p.next()
 	} else {

src/pkg/go/parser/parser_test.go

@@ -5,6 +5,7 @@
 package parser
 
 import (
+	"fmt"
 	"go/ast"
 	"go/token"
 	"os"
@@ -204,3 +205,32 @@ func TestVarScope(t *testing.T) {
 		}
 	}
 }
+
+var imports = map[string]bool{
+	"a":        true,
+	"a/b":      true,
+	"a.b":      true,
+	"m\x61th":  true,
+	"greek/αβ": true,
+	"":         false,
+	"\x00":     false,
+	"\x7f":     false,
+	"a!":       false,
+	"a b":      false,
+	`a\b`:      false,
+	"`a`":      false,
+	"\x80\x80": false,
+}
+
+func TestImports(t *testing.T) {
+	for path, isValid := range imports {
+		src := fmt.Sprintf("package p; import %q", path)
+		_, err := ParseFile(fset, "", src, 0)
+		switch {
+		case err != nil && isValid:
+			t.Errorf("ParseFile(%s): got %v; expected no error", src, err)
+		case err == nil && !isValid:
+			t.Errorf("ParseFile(%s): got no error; expected one", src)
+		}
+	}
+}