create helper function split_first_extension

src/commands/compress.rs

@@ -9,6 +9,7 @@ use crate::{
     archive,
     commands::warn_user_about_in_memory_zip_compression,
     extension::{
+        split_first_extension,
         CompressionFormat::{self, *},
         Extension,
     },
@@ -69,11 +70,13 @@ pub fn compress_files(
         Ok(encoder)
     };
 
-    for format in formats.iter().flat_map(Extension::iter).skip(1).collect::<Vec<_>>().iter().rev() {
+    let (first_extension, extensions) = split_first_extension(&formats);
+
+    for format in extensions.iter().rev() {
         writer = chain_writer_encoder(format, writer)?;
     }
 
-    match formats[0].compression_formats[0] {
+    match first_extension {
         Gzip | Bzip | Lz4 | Lzma | Snappy | Zstd => {
             let _progress = Progress::new_accessible_aware(
                 total_input_size,
@@ -81,7 +84,7 @@ pub fn compress_files(
                 Some(Box::new(move || output_file_path.metadata().expect("file exists").len())),
             );
 
-            writer = chain_writer_encoder(&formats[0].compression_formats[0], writer)?;
+            writer = chain_writer_encoder(&first_extension, writer)?;
             let mut reader = fs::File::open(&files[0]).unwrap();
             io::copy(&mut reader, &mut writer)?;
         }

src/commands/decompress.rs

@@ -9,6 +9,7 @@ use fs_err as fs;
 use crate::{
     commands::warn_user_about_in_memory_zip_decompression,
     extension::{
+        split_first_extension,
         CompressionFormat::{self, *},
         Extension,
     },
@@ -34,6 +35,7 @@ pub fn decompress_file(
     assert!(output_dir.exists());
     let total_input_size = input_file_path.metadata().expect("file exists").len();
     let reader = fs::File::open(&input_file_path)?;
+
     // Zip archives are special, because they require io::Seek, so it requires it's logic separated
     // from decoder chaining.
     //
@@ -41,7 +43,7 @@ pub fn decompress_file(
     // in-memory decompression/copying first.
     //
     // Any other Zip decompression done can take up the whole RAM and freeze ouch.
-    if formats.len() == 1 && *formats[0].compression_formats == [Zip] {
+    if let [Extension { compression_formats: [Zip], .. }] = formats.as_slice() {
         let zip_archive = zip::ZipArchive::new(reader)?;
         let files = if let ControlFlow::Continue(files) = smart_unpack(
             Box::new(move |output_dir| {
@@ -93,13 +95,15 @@ pub fn decompress_file(
         Ok(decoder)
     };
 
-    for format in formats.iter().flat_map(Extension::iter).skip(1).collect::<Vec<_>>().iter().rev() {
+    let (first_extension, extensions) = split_first_extension(&formats);
+
+    for format in extensions.iter().rev() {
         reader = chain_reader_decoder(format, reader)?;
     }
 
-    let files_unpacked = match formats[0].compression_formats[0] {
+    let files_unpacked = match first_extension {
         Gzip | Bzip | Lz4 | Lzma | Snappy | Zstd => {
-            reader = chain_reader_decoder(&formats[0].compression_formats[0], reader)?;
+            reader = chain_reader_decoder(&first_extension, reader)?;
 
             let writer = utils::create_or_ask_overwrite(&output_file_path, question_policy)?;
             if writer.is_none() {

src/extension.rs

@@ -171,3 +171,10 @@ mod tests {
         assert_eq!(formats, vec![&Tar, &Gzip]);
     }
 }
+
+// Panics if formats has an empty list of compression formats
+pub fn split_first_extension(formats: &[Extension]) -> (CompressionFormat, Vec<CompressionFormat>) {
+    let mut extensions: Vec<CompressionFormat> = formats.iter().flat_map(Extension::iter).copied().collect();
+    let first_extension = extensions.remove(0);
+    (first_extension, extensions)
+}