Convert to let-else syntax

Convert to [let else](https://doc.rust-lang.org/rust-by-example/flow_control/let_else.html) where possible.

Inspired by coreos/bootupd#723 (comment)

Author: HuijingHei

src/bios.rs

@@ -95,9 +95,7 @@ impl Component for Bios {
         device: &str,
         _update_firmware: bool,
     ) -> Result<InstalledContent> {
-        let meta = if let Some(meta) = get_component_update(src_root, self)? {
-            meta
-        } else {
+        let Some(meta) = get_component_update(src_root, self)? else {
             anyhow::bail!("No update metadata for component {} found", self.name());
         };
 

src/bootupd.rs

@@ -249,9 +249,7 @@ pub(crate) fn adopt_and_update(name: &str) -> Result<ContentMetadata> {
 
     ensure_writable_boot()?;
 
-    let update = if let Some(update) = component.query_update(&sysroot)? {
-        update
-    } else {
+    let Some(update) = component.query_update(&sysroot)? else {
         anyhow::bail!("Component {} has no available update", name);
     };
     let mut state_guard =
@@ -270,12 +268,10 @@ pub(crate) fn adopt_and_update(name: &str) -> Result<ContentMetadata> {
 pub(crate) fn validate(name: &str) -> Result<ValidationResult> {
     let state = SavedState::load_from_disk("/")?.unwrap_or_default();
     let component = component::new_from_name(name)?;
-    let inst = if let Some(inst) = state.installed.get(name) {
-        inst.clone()
-    } else {
+    let Some(inst) = state.installed.get(name) else {
         anyhow::bail!("Component {} is not installed", name);
     };
-    component.validate(&inst)
+    component.validate(inst)
 }
 
 pub(crate) fn status() -> Result<Status> {

src/efi.rs

@@ -283,9 +283,7 @@ impl Component for Efi {
         device: &str,
         update_firmware: bool,
     ) -> Result<InstalledContent> {
-        let meta = if let Some(meta) = get_component_update(src_root, self)? {
-            meta
-        } else {
+        let Some(meta) = get_component_update(src_root, self)? else {
             anyhow::bail!("No update metadata for component {} found", self.name());
         };
         log::debug!("Found metadata {}", meta.version);

src/filetree.rs

@@ -104,9 +104,7 @@ impl FileTree {
         let mut ret = HashMap::new();
         for entry in dir.list_dir(".")? {
             let entry = entry?;
-            let name = if let Some(name) = entry.file_name().to_str() {
-                name
-            } else {
+            let Some(name) = entry.file_name().to_str() else {
                 bail!("Invalid UTF-8 filename: {:?}", entry.file_name())
             };
             if name.starts_with(TMP_PREFIX) {
@@ -239,9 +237,7 @@ impl FileTree {
 fn cleanup_tmp(dir: &openat::Dir) -> Result<()> {
     for entry in dir.list_dir(".")? {
         let entry = entry?;
-        let name = if let Some(name) = entry.file_name().to_str() {
-            name
-        } else {
+        let Some(name) = entry.file_name().to_str() else {
             // Skip invalid UTF-8 for now, we will barf on it later though.
             continue;
         };

src/util.rs

@@ -37,9 +37,7 @@ pub(crate) fn filenames(dir: &openat::Dir) -> Result<HashSet<String>> {
     let mut ret = HashSet::new();
     for entry in dir.list_dir(".")? {
         let entry = entry?;
-        let name = if let Some(name) = entry.file_name().to_str() {
-            name
-        } else {
+        let Some(name) = entry.file_name().to_str() else {
             bail!("Invalid UTF-8 filename: {:?}", entry.file_name())
         };
         match dir.get_file_type(&entry)? {