Add append support for filesystem files

src/config/file.rs

@@ -1,5 +1,9 @@
 use std::fmt::Display;
 
+fn is_false(value: &bool) -> bool {
+    !*value
+}
+
 #[derive(Clone, Debug, Default, Deserialize, Serialize)]
 pub struct FileConfig {
     pub path: String,
@@ -15,6 +19,8 @@ pub struct FileConfig {
     pub recursive_chown: bool,
     #[serde(default)]
     pub postinstall: bool,
+    #[serde(default, skip_serializing_if = "is_false")]
+    pub append: bool,
 }
 
 impl FileConfig {
@@ -68,6 +74,9 @@ impl Display for FileConfig {
             if self.postinstall {
                 write!(f, "!")?;
             }
+            if self.append {
+                write!(f, " append=yes")?;
+            }
         }
         if let Some(uid) = self.uid {
             write!(f, " uid={}", uid)?;

src/config/file_impl.rs

@@ -60,9 +60,19 @@ impl crate::FileConfig {
             })?;
             Ok(())
         } else {
-            println!("Create file {}", target_file.display());
-            let mut file = File::create(&target_file)
-                .with_context(|| format!("failed to create file {}", target_file.display()))?;
+            let action = if self.append { "Append" } else { "Create" };
+            println!("{action} file {}", target_file.display());
+
+            let mut file = if self.append {
+                fs::OpenOptions::new()
+                    .create(true)
+                    .append(true)
+                    .open(&target_file)
+                    .with_context(|| format!("failed to append file {}", target_file.display()))?
+            } else {
+                File::create(&target_file)
+                    .with_context(|| format!("failed to create file {}", target_file.display()))?
+            };
             file.write_all(self.data.as_bytes())?;
 
             self.apply_perms(target_file)