yaml/v2: Detect file patterns automatically (#2873)

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### Proposed changes

<!--Give us a brief description of what you've done and what it solves.
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This PR teaches `ConfigGroup` to detect whether a given file path is a
glob pattern, to make the handling of non-existent files be consistent
w.r.t `ConfigFile`. In other words, `*.yaml` MAY match a file whereas
`manifest.yaml` MUST match a file.

The detection code looks for special characters '*', '?', and '[' and
respects the escape syntax. Intended to be consistent with:
[https://pkg.go.dev/path/filepath#Match](https://pkg.go.dev/path/filepath#Match)

An alternative to doing pattern detection would be:
1. to expose a `glob` property to toggle globbing, or 
2. a `patterns` property alongside the `files` property for patterns and
non-patterns respectively

### Related issues (optional)

<!--Refer to related PRs or issues: #1234, or 'Fixes #1234' or 'Closes
#1234'.
Or link to full URLs to issues or pull requests in other GitHub
repositories. -->
Closes #2871

provider/pkg/provider/yaml/v2/yaml.go

@@ -24,6 +24,7 @@ import (
 	"net/url"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 
 	"github.com/pkg/errors"
@@ -70,10 +71,10 @@ func ParseDecodeYamlFiles(ctx *pulumi.Context, args *ParseArgs, glob bool, clien
 			}
 			yamls = append(yamls, string(yaml))
 		} else {
-			// Otherwise, assume this is a path to a file on disk. If globbing is enabled, we might have
-			// multiple files -- otherwise just read a singular file.
+			// Otherwise, assume this is a path to a file on disk. If globbing is enabled and a pattern is provided, we might have
+			// multiple files -- otherwise just read a singular file and fail if it doesn't exist.
 			var files []string
-			if glob {
+			if glob && isGlobPattern(file) {
 				files, err = filepath.Glob(file)
 				if err != nil {
 					return pulumi.ArrayOutput{}, errors.Wrapf(err, "expanding glob")
@@ -246,3 +247,11 @@ func printUnstructured(obj *unstructured.Unstructured) string {
 	bytes, _ := obj.MarshalJSON()
 	return truncate(strings.TrimSpace(string(bytes)), 100)
 }
+
+// globPatternRegexp is a regular expression that matches any of the special characters in a glob pattern.
+// see: https://pkg.go.dev/path/filepath#Match
+var globPatternRegexp = regexp.MustCompile(`(?:^|[^\\])[*?\[]`)
+
+func isGlobPattern(pattern string) bool {
+	return globPatternRegexp.Match([]byte(pattern))
+}

provider/pkg/provider/yaml/v2/yaml_test.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"os"
 	"path/filepath"
+	"testing"
 
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
@@ -26,6 +27,7 @@ import (
 	. "github.com/pulumi/pulumi-kubernetes/tests/v4/gomega"
 	"github.com/pulumi/pulumi/sdk/v3/go/pulumi"
 	"github.com/pulumi/pulumi/sdk/v3/go/pulumi/internals"
+	"github.com/stretchr/testify/assert"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 )
 
@@ -195,20 +197,34 @@ var _ = Describe("ParseDecodeYamlFiles", func() {
 	})
 
 	Describe("files", func() {
-		Context("when the file doesn't exist (glob mode)", func() {
+		Describe("globbing", func() {
 			BeforeEach(func() {
 				glob = true
-				args.Files = []string{"nosuchfile.yaml"}
 			})
-			It("should do nothing", func(ctx context.Context) {
-				_, err := parse(ctx)
-				Expect(err).ShouldNot(HaveOccurred())
+
+			Context("when the pattern matches no files", func() {
+				BeforeEach(func() {
+					args.Files = []string{"nosuchfile-*.yaml"}
+				})
+				It("should do nothing", func(ctx context.Context) {
+					_, err := parse(ctx)
+					Expect(err).ShouldNot(HaveOccurred())
+				})
+			})
+
+			Context("when the pattern matches some files", func() {
+				BeforeEach(func() {
+					tempDir := GinkgoTB().TempDir()
+					err := os.WriteFile(filepath.Join(tempDir, "manifest.yaml"), []byte(manifest), 0o600)
+					Expect(err).ShouldNot(HaveOccurred())
+					args.Files = []string{filepath.Join(tempDir, "*.yaml")}
+				})
+				commonAssertions()
 			})
 		})
 
-		Context("when the file doesn't exist (non-glob mode)", func() {
+		Context("when the file doesn't exist", func() {
 			BeforeEach(func() {
-				glob = false
 				args.Files = []string{"nosuchfile.yaml"}
 			})
 			It("should fail", func(ctx context.Context) {
@@ -330,3 +346,34 @@ var _ = Describe("ParseDecodeYamlFiles", func() {
 		})
 	})
 })
+
+func TestIsGlobPattern(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		pattern  string
+		expected bool
+	}{
+		{pattern: `manifest.yaml`, expected: false},
+		{pattern: `*.yaml`, expected: true},
+		{pattern: `*`, expected: true},
+		{pattern: `test-?.yaml`, expected: true},
+		{pattern: `ba[rz].yaml`, expected: true},
+		{pattern: `escaped-\*.yaml`, expected: false},
+		{pattern: `\*.yaml`, expected: false},
+	}
+
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.pattern, func(t *testing.T) {
+			t.Parallel()
+
+			isPattern := isGlobPattern(tt.pattern)
+			if tt.expected {
+				assert.Truef(t, isPattern, "expected %q to be a pattern", tt.pattern)
+			} else {
+				assert.Falsef(t, isPattern, "expected %q to not be a pattern", tt.pattern)
+			}
+		})
+	}
+}