[filestorage] - Add directory validation for compaction on-rebound (#35114)

**Description:** 

Currently, we only verify the existence of the compaction directory when
`compaction.on_start` is enabled. This check should also be performed
when `compaction.on_rebound` is enabled.
Otherwise, we encounter continuous error notifications due to the
directory not existing, which results in compaction failures.

**Testing:** Added

Author: VihasMakwana

.chloggen/add-validation-for-rebound.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: filestorage
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add directory validation for compaction on-rebound
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [35114]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

extension/storage/filestorage/config.go

@@ -53,7 +53,7 @@ type CompactionConfig struct {
 
 func (cfg *Config) Validate() error {
 	var dirs []string
-	if cfg.Compaction.OnStart {
+	if cfg.Compaction.OnStart || cfg.Compaction.OnRebound {
 		dirs = []string{cfg.Directory, cfg.Compaction.Directory}
 	} else {
 		dirs = []string{cfg.Directory}

extension/storage/filestorage/config_test.go

@@ -95,3 +95,67 @@ func TestHandleProvidingFilePathAsDirWithAnError(t *testing.T) {
 	require.Error(t, err)
 	require.EqualError(t, err, file.Name()+" is not a directory")
 }
+
+func TestCompactionDirectory(t *testing.T) {
+	f := NewFactory()
+	tests := []struct {
+		name   string
+		config func(*testing.T) *Config
+		err    error
+	}{
+		{
+			name: "directory-must-exists-error",
+			config: func(t *testing.T) *Config {
+				cfg := f.CreateDefaultConfig().(*Config)
+				cfg.Directory = t.TempDir()             // actual directory
+				cfg.Compaction.Directory = "/not/a/dir" // not a directory
+				cfg.Compaction.OnRebound = true
+				cfg.Compaction.OnStart = true
+				return cfg
+			},
+			err: os.ErrNotExist,
+		},
+		{
+			name: "directory-must-exists-error-on-start",
+			config: func(t *testing.T) *Config {
+				cfg := f.CreateDefaultConfig().(*Config)
+				cfg.Directory = t.TempDir()             // actual directory
+				cfg.Compaction.Directory = "/not/a/dir" // not a directory
+				cfg.Compaction.OnRebound = false
+				cfg.Compaction.OnStart = true
+				return cfg
+			},
+			err: os.ErrNotExist,
+		},
+		{
+			name: "directory-must-exists-error-on-rebound",
+			config: func(t *testing.T) *Config {
+				cfg := f.CreateDefaultConfig().(*Config)
+				cfg.Directory = t.TempDir()             // actual directory
+				cfg.Compaction.Directory = "/not/a/dir" // not a directory
+				cfg.Compaction.OnRebound = true
+				cfg.Compaction.OnStart = false
+				return cfg
+			},
+			err: os.ErrNotExist,
+		},
+		{
+			name: "compaction-disabled-no-error",
+			config: func(t *testing.T) *Config {
+				cfg := f.CreateDefaultConfig().(*Config)
+				cfg.Directory = t.TempDir()             // actual directory
+				cfg.Compaction.Directory = "/not/a/dir" // not a directory
+				cfg.Compaction.OnRebound = false
+				cfg.Compaction.OnStart = false
+				return cfg
+			},
+			err: nil,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			require.ErrorIs(t, component.ValidateConfig(test.config(t)), test.err)
+		})
+	}
+
+}