Support negative globs for partition globs (#92)

internal/fs/local.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"path/filepath"
 	"sort"
+	"strings"
 
 	doublestar "github.com/bmatcuk/doublestar/v4"
 
@@ -52,14 +53,25 @@ func (l Local) Glob(pattern string) ([]string, error) {
 }
 
 func (l Local) GlobMany(patterns []string) ([]string, error) {
-	pathSet := make(map[string]struct{})
+	pathSet := make(map[string]bool)
 	for _, pattern := range patterns {
+		isNegation := false
+
+		if strings.HasPrefix(pattern, "!") {
+			isNegation = true
+			pattern = strings.TrimPrefix(pattern, "!")
+		}
+
 		expandedPaths, err := l.Glob(pattern)
 		if err != nil {
 			return nil, errors.WithStack(err)
 		}
 		for _, filePath := range expandedPaths {
-			pathSet[filePath] = struct{}{}
+			if isNegation {
+				delete(pathSet, filePath)
+			} else {
+				pathSet[filePath] = true
+			}
 		}
 	}
 

internal/fs/local_test.go

@@ -39,6 +39,22 @@ var _ = Describe("fs.GlobMany", func() {
 		}))
 	})
 
+	It("supports negation", func() {
+		fs := fs.Local{}
+		expandedPaths, _ := fs.GlobMany([]string{
+			"../../test/fixtures/integration-tests/partition/*_spec.rb",
+			"!../../test/fixtures/integration-tests/partition/a_spec.rb",
+			"!../../test/fixtures/integration-tests/partition/b_spec.rb",
+			"../../test/fixtures/integration-tests/partition/b_spec.rb",
+		})
+
+		Expect(expandedPaths).To(Equal([]string{
+			"../../test/fixtures/integration-tests/partition/b_spec.rb",
+			"../../test/fixtures/integration-tests/partition/c_spec.rb",
+			"../../test/fixtures/integration-tests/partition/d_spec.rb",
+		}))
+	})
+
 	It("expands multiple glob patterns only returning unique paths", func() {
 		fs := fs.Local{}
 		expandedPaths, _ := fs.GlobMany([]string{