fix: Handle complex Exec keys in desktop entries (#930)

Closes: #922, #924, #925, #928

My original patch, #891, mishandled Exec keys. The ordering of arguments
matters for the keys, such as for Flatpak apps.

src/mime_app.rs

@@ -27,14 +27,17 @@ pub fn exec_to_command(
 ) -> Option<Vec<process::Command>> {
     let args_vec = shlex::split(exec)?;
     let program = args_vec.first()?;
+    // Skip program to make indexing easier
+    let args_vec = &args_vec[1..];
 
     // Base Command instance(s)
     // 1. We may need to launch multiple of the same process.
     // 2. Each of those processes will need to be passed args from exec.
     // 3. Each of those args may appear in any order.
+    // 4. Arg order should be preserved.
     //
-    // So, we'll go through exec in two passes. The first pass handles paths (%f etc) while the
-    // second passes extra, non-% args to each processes.
+    // So, we'll go through exec in two passes. The first pass handles paths (%f etc) and args up
+    // to the field code followed by the second which passes extra, non-% args to each processes.
     //
     // While it'd be marginally faster to process everything in one pass, that's problematic:
     // 1. path_opt may need to be cloned because it may be moved on each iteration (borrowck
@@ -42,11 +45,15 @@ pub fn exec_to_command(
     // 2. We have to keep track of which modifier (%f etc) we've used/seen already
     // 3. We have to keep track of which processes received non-modifier args which gets messy fast
     // 4. `exec` is likely small so looping over it twice is not a big deal
-    let args_handler = args_vec
+    let field_code_pos = args_vec
         .iter()
-        .find(|arg| EXEC_HANDLERS.contains(&arg.as_str()));
+        .position(|arg| EXEC_HANDLERS.contains(&arg.as_str()));
+    let args_handler = field_code_pos.and_then(|i| args_vec.get(i));
     // msrv
     // .inspect(|handler| log::trace!("Found paths handler: {handler} for exec: {exec}"));
+    // Number of args before the field code.
+    // This won't be an off by one err below because take is not zero indexed.
+    let field_code_pos = field_code_pos.unwrap_or_default();
     let mut processes = match args_handler.map(|s| s.as_str()) {
         Some("%f") => {
             let mut processes = Vec::with_capacity(path_opt.len());
@@ -59,7 +66,13 @@ pub fn exec_to_command(
 
                 // Passing multiple paths to %f should open an instance per path
                 let mut process = process::Command::new(program);
-                process.arg(path);
+                process.args(
+                    args_vec
+                        .iter()
+                        .map(AsRef::as_ref)
+                        .take(field_code_pos)
+                        .chain(std::iter::once(path)),
+                );
                 processes.push(process);
             }
 
@@ -77,7 +90,13 @@ pub fn exec_to_command(
 
             // Launch one instance with all args
             let mut process = process::Command::new(program);
-            process.args(path_opt);
+            process.args(
+                args_vec
+                    .iter()
+                    .map(OsStr::new)
+                    .take(field_code_pos)
+                    .chain(path_opt.iter().map(AsRef::as_ref)),
+            );
 
             vec![process]
         }
@@ -85,29 +104,42 @@ pub fn exec_to_command(
             .iter()
             .map(|path| {
                 let mut process = process::Command::new(program);
-                process.arg(path);
+                process.args(
+                    args_vec
+                        .iter()
+                        .map(OsStr::new)
+                        .take(field_code_pos)
+                        .chain(std::iter::once(path.as_ref())),
+                );
                 process
             })
             .collect(),
         Some("%U") => {
             let mut process = process::Command::new(program);
-            process.args(path_opt);
+            process.args(
+                args_vec
+                    .iter()
+                    .map(OsStr::new)
+                    .take(field_code_pos)
+                    .chain(path_opt.iter().map(AsRef::as_ref)),
+            );
             vec![process]
         }
         Some(invalid) => unreachable!("All valid variants were checked; got: {invalid}"),
         None => vec![process::Command::new(program)],
     };
 
-    // Pass 2: Add every argument that's not % to each process
-    for arg in args_vec.into_iter().skip(1) {
+    // Pass 2: Add remaining arguments that are not % to each process
+    for arg in args_vec.iter().skip(field_code_pos) {
         match arg.as_str() {
-            unsupported
-                if arg.starts_with('%')
-                    && !EXEC_HANDLERS.contains(&unsupported)
-                    && !DEPRECATED_HANDLERS.contains(&unsupported) =>
-            {
-                log::warn!("unsupported Exec code {:?} in {:?}", unsupported, exec);
-                return None;
+            // Consume path field codes or fail on codes we don't handle yet
+            field_code if arg.starts_with('%') => {
+                if !EXEC_HANDLERS.contains(&field_code)
+                    && !DEPRECATED_HANDLERS.contains(&field_code)
+                {
+                    log::warn!("unsupported Exec code {:?} in {:?}", field_code, exec);
+                    return None;
+                }
             }
             arg => {
                 for process in &mut processes {
@@ -116,6 +148,16 @@ pub fn exec_to_command(
             }
         }
     }
+
+    #[cfg(debug_assertions)]
+    for command in &processes {
+        log::debug!(
+            "Parsed program {} with args: {:?}",
+            command.get_program().to_string_lossy(),
+            command.get_args()
+        );
+    }
+
     Some(processes)
 }