Exclude generated code from coverage

Fixes dave#15

README.md

@@ -20,6 +20,11 @@ error rather than a panic.
 ### Notest comments
 Blocks or files with a `// notest` comment are excluded.
 
+### Generated code
+Generated code files, that contain the respective comment line that is
+specified by the [Go Team](https://github.com/golang/go/issues/41196) in
+[`go generate`](https://cs.opensource.google/go/go/+/refs/tags/go1.18:src/cmd/go/internal/generate/generate.go;l=66-73).
+
 ### Blocks returning a error tested to be non-nil
 We only exclude blocks where the error being returned has been tested to be 
 non-nil, so:

scanner/scanner.go

@@ -1,11 +1,14 @@
 package scanner
 
 import (
+	"bytes"
 	"fmt"
 	"go/ast"
 	"go/constant"
 	"go/token"
 	"go/types"
+	"os"
+	"regexp"
 	"strings"
 
 	"github.com/dave/astrid"
@@ -117,6 +120,8 @@ func (c *CodeMap) ScanPackages() error {
 	return nil
 }
 
+var doNotEditRe = regexp.MustCompile(`(?m)^// Code generated .* DO NOT EDIT\.$`)
+
 // ScanPackage scans a single package
 func (p *PackageMap) ScanPackage() error {
 	for _, f := range p.pkg.Syntax {
@@ -130,6 +135,20 @@ func (p *PackageMap) ScanPackage() error {
 			return errors.WithStack(err)
 		}
 	}
+
+	// Exclude complete files, if the code is generated.
+	for _, f := range p.pkg.GoFiles {
+		body, err := os.ReadFile(f)
+		if err != nil {
+			return errors.WithStack(err)
+		}
+		if !doNotEditRe.Match(body) {
+			continue
+		}
+		for i := range bytes.Split(body, []byte("\n")) {
+			p.addExclude(f, i+1)
+		}
+	}
 	return nil
 }
 

scanner/scanner_test.go

@@ -701,6 +701,17 @@ func TestComments(t *testing.T) {
 	test(t, tests)
 }
 
+func TestGenerated(t *testing.T) {
+	tests := map[string]string{
+		"generated": `// Code generated by courtney. DO NOT EDIT.
+			package foo // *
+			func Baz() int { // *
+				return 0 // *
+			} // *`,
+	}
+	test(t, tests)
+}
+
 func test(t *testing.T, tests map[string]string) {
 	for name, source := range tests {
 		env := vos.Mock()
@@ -746,7 +757,9 @@ func test(t *testing.T, tests map[string]string) {
 		notest := regexp.MustCompile("//\\s?notest(\\s//\\s?.*)?$")
 
 		for i, line := range strings.Split(source, "\n") {
-			expected := strings.HasSuffix(line, "// *") || notest.MatchString(line)
+			expected := strings.HasSuffix(line, "// *") ||
+				notest.MatchString(line) ||
+				strings.HasSuffix(line, "// Code generated by courtney. DO NOT EDIT.")
 			if result[i+1] != expected {
 				t.Fatalf("Unexpected state in %s, line %d: %s\n", name, i, strconv.Quote(strings.Trim(line, "\t")))
 			}