handle some block comment to detect generated files (#1161)

pkg/result/processors/autogenerated_exclude.go

@@ -1,9 +1,9 @@
 package processors
 
 import (
-	"bufio"
 	"fmt"
-	"os"
+	"go/parser"
+	"go/token"
 	"path/filepath"
 	"strings"
 
@@ -113,37 +113,15 @@ func (p *AutogeneratedExclude) getOrCreateFileSummary(i *result.Issue) (*ageFile
 }
 
 func getDoc(filePath string) (string, error) {
-	file, err := os.Open(filePath)
+	fset := token.NewFileSet()
+	syntax, err := parser.ParseFile(fset, filePath, nil, parser.PackageClauseOnly|parser.ParseComments)
 	if err != nil {
-		return "", errors.Wrap(err, "failed to open file")
+		return "", errors.Wrap(err, "failed to parse file")
 	}
-	defer file.Close()
-
-	scanner := bufio.NewScanner(file)
-
-	// Issue 954: Some lines can be very long, e.g. auto-generated
-	// embedded resources. Reported on file of 86.2KB.
-	const (
-		maxSize     = 10 * 1024 * 1024 // 10MB should be enough
-		initialSize = 4096             // same as startBufSize in bufio
-	)
-	scanner.Buffer(make([]byte, initialSize), maxSize)
 
 	var docLines []string
-	for scanner.Scan() {
-		line := strings.TrimSpace(scanner.Text())
-		if strings.HasPrefix(line, "//") {
-			text := strings.TrimSpace(strings.TrimPrefix(line, "//"))
-			docLines = append(docLines, text)
-		} else if line == "" || strings.HasPrefix(line, "package") {
-			// go to next line
-		} else {
-			break
-		}
-	}
-
-	if err := scanner.Err(); err != nil {
-		return "", errors.Wrap(err, "failed to scan file")
+	for _, c := range syntax.Comments {
+		docLines = append(docLines, strings.TrimSpace(c.Text()))
 	}
 
 	return strings.Join(docLines, "\n"), nil

pkg/result/processors/testdata/autogen_exclude.go

@@ -3,5 +3,5 @@
 
 // third line
 
-package testdata // no this text
+package testdata // this text also
 // and this text also

pkg/result/processors/testdata/autogen_exclude_block_comment.go

@@ -0,0 +1,16 @@
+/*
+ * first line
+ *
+ * second line
+ * third line
+ */
+
+// and this text also
+
+/*
+this type of block comment also
+*/
+
+/* this one line comment also */
+
+package testdata