fix(tomcat): surface non-IsNotExist errors when checking META-INF/context.xml

os.Stat errors other than IsNotExist (permissions/IO) were treated as
"no context.xml" and silently fell back to a default descriptor, dropping
user-provided Realm/Resource config. Return the error instead.

Author: stokpop

src/java/containers/tomcat.go

@@ -607,7 +607,14 @@ func (t *TomcatContainer) Finalize() error {
 			appContextXML := filepath.Join(buildDir, "META-INF", "context.xml")
 			var contextContent string
 
-			if _, err := os.Stat(appContextXML); err == nil {
+			_, appStatErr := os.Stat(appContextXML)
+			if appStatErr != nil && !os.IsNotExist(appStatErr) {
+				// A non-IsNotExist error (permissions/IO) must not be silently
+				// treated as "no context.xml" — that would drop user-provided
+				// Realm/Resource config. Surface it.
+				return fmt.Errorf("failed to check META-INF/context.xml: %w", appStatErr)
+			}
+			if appStatErr == nil {
 				xmlBytes, err := os.ReadFile(appContextXML)
 				if err != nil {
 					return fmt.Errorf("failed to read META-INF/context.xml: %w", err)

src/java/containers/tomcat_test.go

@@ -139,6 +139,18 @@ var _ = Describe("Tomcat Container", func() {
 			Expect(string(content)).To(ContainSubstring("reloadable=\"false\""))
 		})
 
+		It("returns an error when META-INF/context.xml cannot be stat'd (non-IsNotExist)", func() {
+			// Make META-INF a regular file so os.Stat(META-INF/context.xml) fails
+			// with ENOTDIR (not IsNotExist). The buildpack must surface this rather
+			// than silently falling back to a default descriptor, which would drop
+			// user-provided Realm/Resource config.
+			Expect(os.WriteFile(filepath.Join(buildDir, "META-INF"), []byte("not a dir"), 0644)).To(Succeed())
+
+			err := container.Finalize()
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(ContainSubstring("META-INF/context.xml"))
+		})
+
 		It("merges META-INF/context.xml with realm configuration", func() {
 			metaInfDir := filepath.Join(buildDir, "META-INF")
 			os.MkdirAll(metaInfDir, 0755)