5 files changed, 149 insertions, 17 deletions
diff --git a/tools/nogo/build.go b/tools/nogo/build.go
index 37947b5c3..39c2ae418 100644
--- a/tools/nogo/build.go
+++ b/tools/nogo/build.go
@@ -26,6 +26,9 @@ var (
 	// and should not have any special prefix applied.
 	internalPrefix = fmt.Sprintf("^")
 
+	// internalDefault is applied when no paths are provided.
+	internalDefault = fmt.Sprintf("%s/.*", notPath("external"))
+
 	// externalPrefix is external workspace packages.
 	externalPrefix = "^external/"
 )
diff --git a/tools/nogo/matchers.go b/tools/nogo/matchers.go
index 57a250501..5c39be630 100644
--- a/tools/nogo/matchers.go
+++ b/tools/nogo/matchers.go
@@ -16,7 +16,6 @@ package nogo
 
 import (
 	"go/token"
-	"path/filepath"
 	"regexp"
 	"strings"
 
@@ -44,11 +43,30 @@ type pathRegexps struct {
 func buildRegexps(prefix string, args ...string) []*regexp.Regexp {
 	result := make([]*regexp.Regexp, 0, len(args))
 	for _, arg := range args {
-		result = append(result, regexp.MustCompile(filepath.Join(prefix, arg)))
+		result = append(result, regexp.MustCompile(prefix+arg))
 	}
 	return result
 }
 
+// notPath works around the lack of backtracking.
+//
+// It is used to construct a regular expression for non-matching components.
+func notPath(name string) string {
+	sb := strings.Builder{}
+	sb.WriteString("(")
+	for i := range name {
+		if i > 0 {
+			sb.WriteString("|")
+		}
+		sb.WriteString(name[:i])
+		sb.WriteString("[^")
+		sb.WriteByte(name[i])
+		sb.WriteString("/][^/]*")
+	}
+	sb.WriteString(")")
+	return sb.String()
+}
+
 // ShouldReport implements matcher.ShouldReport.
 func (p *pathRegexps) ShouldReport(d analysis.Diagnostic, fs *token.FileSet) bool {
 	fullPos := fs.Position(d.Pos).String()
@@ -79,7 +97,7 @@ func externalExcluded(paths ...string) *pathRegexps {
 // internalMatches returns a path matcher for internal packages.
 func internalMatches() *pathRegexps {
 	return &pathRegexps{
-		expr:    buildRegexps(internalPrefix, ".*"),
+		expr:    buildRegexps(internalPrefix, internalDefault),
 		include: true,
 	}
 }
diff --git a/tools/nogo/nogo.go b/tools/nogo/nogo.go
index 40e48540d..120fdcff5 100644
--- a/tools/nogo/nogo.go
+++ b/tools/nogo/nogo.go
@@ -202,29 +202,41 @@ func checkStdlib(config *stdlibConfig, ac map[*analysis.Analyzer]matcher) ([]str
 		config.Srcs[i] = path.Clean(config.Srcs[i])
 	}
 
-	// Calculate the root directory.
-	longestPrefix := path.Dir(config.Srcs[0])
-	for _, file := range config.Srcs[1:] {
-		for i := 0; i < len(file) && i < len(longestPrefix); i++ {
-			if file[i] != longestPrefix[i] {
-				// Truncate here; will stop the loop.
-				longestPrefix = longestPrefix[:i]
-				break
-			}
+	// Calculate the root source directory. This is always a directory
+	// named 'src', of which we simply take the first we find. This is a
+	// bit fragile, but works for all currently known Go source
+	// configurations.
+	//
+	// Note that there may be extra files outside of the root source
+	// directory; we simply ignore those.
+	rootSrcPrefix := ""
+	for _, file := range config.Srcs {
+		const src = "/src/"
+		i := strings.Index(file, src)
+		if i == -1 {
+			// Superfluous file.
+			continue
 		}
-	}
-	if len(longestPrefix) > 0 && longestPrefix[len(longestPrefix)-1] != '/' {
-		longestPrefix += "/"
+
+		// Index of first character after /src/.
+		i += len(src)
+		rootSrcPrefix = file[:i]
+		break
 	}
 
 	// Aggregate all files by directory.
 	packages := make(map[string]*packageConfig)
 	for _, file := range config.Srcs {
+		if !strings.HasPrefix(file, rootSrcPrefix) {
+			// Superflouous file.
+			continue
+		}
+
 		d := path.Dir(file)
-		if len(longestPrefix) >= len(d) {
+		if len(rootSrcPrefix) >= len(d) {
 			continue // Not a file.
 		}
-		pkg := path.Dir(file)[len(longestPrefix):]
+		pkg := d[len(rootSrcPrefix):]
 		// Skip cmd packages and obvious test files: see above.
 		if strings.HasPrefix(pkg, "cmd/") || strings.HasSuffix(file, "_test.go") {
 			continue
@@ -303,6 +315,11 @@ func checkStdlib(config *stdlibConfig, ac map[*analysis.Analyzer]matcher) ([]str
 		checkOne(pkg)
 	}
 
+	// Sanity check.
+	if len(stdlibFacts) == 0 {
+		return nil, nil, fmt.Errorf("no stdlib facts found: misconfiguration?")
+	}
+
 	// Write out all findings.
 	factData, err := json.Marshal(stdlibFacts)
 	if err != nil {
diff --git a/tools/nogo/util/BUILD b/tools/nogo/util/BUILD
new file mode 100644
index 000000000..7ab340b51
--- /dev/null
+++ b/tools/nogo/util/BUILD
@@ -0,0 +1,9 @@
+load("//tools:defs.bzl", "go_library")
+
+package(licenses = ["notice"])
+
+go_library(
+    name = "util",
+    srcs = ["util.go"],
+    visibility = ["//visibility:public"],
+)
diff --git a/tools/nogo/util/util.go b/tools/nogo/util/util.go
new file mode 100644
index 000000000..919fec799
--- /dev/null
+++ b/tools/nogo/util/util.go
@@ -0,0 +1,85 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package util contains nogo-related utilities.
+package util
+
+import (
+	"fmt"
+	"io/ioutil"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+// findingRegexp is used to parse findings.
+var findingRegexp = regexp.MustCompile(`([a-zA-Z0-9_\/\.-]+): (-|([a-zA-Z0-9_\/\.-]+):([0-9]+)(:([0-9]+))?): (.*)`)
+
+const (
+	categoryIndex        = 1
+	fullPathAndLineIndex = 2
+	fullPathIndex        = 3
+	lineIndex            = 4
+	messageIndex         = 7
+)
+
+// Finding is a single finding.
+type Finding struct {
+	Category string
+	Path     string
+	Line     int
+	Message  string
+}
+
+// ExtractFindingsFromFile loads findings from a file.
+func ExtractFindingsFromFile(filename string) ([]Finding, error) {
+	content, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return nil, err
+	}
+	return ExtractFindingsFromBytes(content)
+}
+
+// ExtractFindingsFromBytes loads findings from bytes.
+func ExtractFindingsFromBytes(content []byte) (findings []Finding, err error) {
+	lines := strings.Split(string(content), "\n")
+	for _, singleLine := range lines {
+		// Skip blank lines.
+		singleLine = strings.TrimSpace(singleLine)
+		if singleLine == "" {
+			continue
+		}
+		m := findingRegexp.FindStringSubmatch(singleLine)
+		if m == nil {
+			// We shouldn't see findings like this.
+			return findings, fmt.Errorf("poorly formated line: %v", singleLine)
+		}
+		if m[fullPathAndLineIndex] == "-" {
+			continue // No source file available.
+		}
+		// Cleanup the message.
+		message := m[messageIndex]
+		message = strings.Replace(message, " → ", "\n → ", -1)
+		message = strings.Replace(message, " or ", "\n or ", -1)
+		// Construct a new annotation.
+		lineNumber, _ := strconv.ParseUint(m[lineIndex], 10, 32)
+		findings = append(findings, Finding{
+			Category: m[categoryIndex],
+			Path:     m[fullPathIndex],
+			Line:     int(lineNumber),
+			Message:  message,
+		})
+	}
+	return findings, nil
+}