From 3138ebd1a319a580551f16f65b6677084a9c8d00 Mon Sep 17 00:00:00 2001
From: eunwoo song <presentsong@naver.com>
Date: Mon, 7 Sep 2026 03:17:21 +0900
Subject: [PATCH 1/2] fix(cli): reject invalid scan roots

Validate root paths before the scanner starts so a typo cannot look like a successful empty disk report. Keep the check in the CLI because inaccessible descendants remain a recoverable scanner concern.

Signed-off-by: eunwoo song <presentsong@naver.com>
---
 CHANGELOG.md                   |  2 ++
 crates/diskern-cli/src/main.rs | 38 ++++++++++++++++++++++++++++++++--
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 96bfe77..0ecd1d8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -47,6 +47,8 @@ All notable changes to Diskern are documented here. The format follows
 
 ### Fixed
 
+- `diskern scan` now rejects missing and nonexistent roots instead of
+  reporting a successful empty scan
 - Restoring a quarantined file across filesystems no longer fails with
   `EXDEV`
 - Restore refuses when something is already at the original path, rather
diff --git a/crates/diskern-cli/src/main.rs b/crates/diskern-cli/src/main.rs
index b312433..2b5bd4d 100644
--- a/crates/diskern-cli/src/main.rs
+++ b/crates/diskern-cli/src/main.rs
@@ -1,4 +1,4 @@
-use anyhow::Result;
+use anyhow::{bail, Result};
 use clap::{Parser, Subcommand, ValueEnum};
 use diskern_core::{report, rules::RulesDb, scanner, Category, Finding, Verdict};
 use std::path::PathBuf;
@@ -19,6 +19,7 @@ enum Command {
     /// Read-only scan: find duplicates, caches, and reclaimable space.
     Scan {
         /// Directories to scan
+        #[arg(required = true)]
         roots: Vec<PathBuf>,
         /// Emit full JSON report instead of a summary
         #[arg(long)]
@@ -183,6 +184,15 @@ fn print_findings(findings: &[&Finding], top: usize) {
     }
 }
 
+fn validate_roots(roots: &[PathBuf]) -> Result<()> {
+    for root in roots {
+        if !root.exists() {
+            bail!("scan root does not exist: {}", root.display());
+        }
+    }
+    Ok(())
+}
+
 fn main() -> Result<()> {
     let cli = Cli::parse();
     match cli.command {
@@ -192,6 +202,7 @@ fn main() -> Result<()> {
             top,
             verdict,
         } => {
+            validate_roots(&roots)?;
             let opts = scanner::ScanOptions {
                 roots,
                 ..Default::default()
@@ -259,7 +270,30 @@ fn main() -> Result<()> {
 
 #[cfg(test)]
 mod tests {
-    use super::human_bytes;
+    use super::{human_bytes, validate_roots, Cli};
+    use clap::{error::ErrorKind, Parser};
+    use std::path::PathBuf;
+
+    #[test]
+    fn scan_requires_at_least_one_root() {
+        let error = match Cli::try_parse_from(["diskern", "scan"]) {
+            Ok(_) => panic!("scan without roots should be rejected"),
+            Err(error) => error,
+        };
+
+        assert_eq!(error.kind(), ErrorKind::MissingRequiredArgument);
+    }
+
+    #[test]
+    fn nonexistent_scan_root_is_rejected_before_scanning() {
+        let missing = PathBuf::from("diskern-test-root-that-does-not-exist");
+        let error = validate_roots(std::slice::from_ref(&missing)).unwrap_err();
+
+        assert_eq!(
+            error.to_string(),
+            format!("scan root does not exist: {}", missing.display())
+        );
+    }
 
     #[test]
     fn scales_to_a_readable_unit() {

From c65f04c83fee4b9143e515dbf61ed20824955578 Mon Sep 17 00:00:00 2001
From: eunwoo song <presentsong@naver.com>
Date: Wed, 9 Sep 2026 08:21:59 +0900
Subject: [PATCH 2/2] fix(cli): preserve scan root context

---
 crates/diskern-cli/src/main.rs | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/crates/diskern-cli/src/main.rs b/crates/diskern-cli/src/main.rs
index 264f1e8..7bb1b51 100644
--- a/crates/diskern-cli/src/main.rs
+++ b/crates/diskern-cli/src/main.rs
@@ -220,7 +220,10 @@ fn load_rules(path: Option<&std::path::Path>) -> Result<RulesDb> {
 
 fn validate_roots(roots: &[PathBuf]) -> Result<()> {
     for root in roots {
-        if !root.try_exists()? {
+        if !root
+            .try_exists()
+            .with_context(|| format!("could not check scan root '{}'", root.display()))?
+        {
             bail!("scan root does not exist: {}", root.display());
         }
     }
@@ -341,6 +344,21 @@ mod tests {
         );
     }
 
+    #[test]
+    fn unreadable_scan_root_error_names_the_root() {
+        let temp = tempfile::tempdir().unwrap();
+        let file = temp.path().join("file");
+        std::fs::write(&file, b"not a directory").unwrap();
+        let invalid_root = file.join("child");
+
+        let error = validate_roots(std::slice::from_ref(&invalid_root)).unwrap_err();
+
+        assert_eq!(
+            error.to_string(),
+            format!("could not check scan root '{}'", invalid_root.display())
+        );
+    }
+
     #[test]
     fn plural_returns_empty_only_for_singular() {
         assert_eq!(plural(0), "s");