Allow overwriting argv with function -a and -V

Previously, if you called a function parameter 'argv', within the body
of the function, argv would be set to *all* the arguments to the
function, and not the one indicated by the parameter name.
The same behaviour happened if you inherited a variable named 'argv'.
Both behaviours were quite surprising, so this commit makes things more
obvious, although they could alternatively simply be made errors.

Part of #11780

doc_src/cmds/function.rst

@@ -21,7 +21,7 @@ A function is a list of commands that will be executed when the name of the func
 The following options are available:
 
 **-a** *NAMES* or **--argument-names** *NAMES*
-    Assigns the value of successive command-line arguments to the names given in *NAMES* (separated by space). These are the same arguments given in :envvar:`argv`, and are still available there. See also :ref:`Argument Handling <variables-argv>`.
+    Assigns the value of successive command-line arguments to the names given in *NAMES* (separated by spaces). These are the same arguments given in :envvar:`argv`, and are still available there (unless ``--inherit-variable argv`` was used or one of the given *NAMES* is ``argv``). See also :ref:`Argument Handling <variables-argv>`.
 
 **-d** *DESCRIPTION* or **--description** *DESCRIPTION*
     A description of what the function does, suitable as a completion description.

src/exec.rs

@@ -948,7 +948,11 @@ fn function_prepare_environment(
     // 2. inherited variables
     // 3. argv
 
+    let mut overwrite_argv = false;
     for (idx, named_arg) in props.named_arguments.iter().enumerate() {
+        if named_arg == L!("argv") {
+            overwrite_argv = true
+        };
         if idx < argv.len() {
             vars.set_one(named_arg, EnvMode::LOCAL | EnvMode::USER, argv[idx].clone());
         } else {
@@ -957,10 +961,15 @@ fn function_prepare_environment(
     }
 
     for (key, value) in &*props.inherit_vars {
+        if key == L!("argv") {
+            overwrite_argv = true
+        };
         vars.set(key, EnvMode::LOCAL | EnvMode::USER, value.clone());
     }
 
-    vars.set_argv(argv);
+    if !overwrite_argv {
+        vars.set_argv(argv);
+    }
     fb
 }
 

tests/checks/function.fish

@@ -192,4 +192,26 @@ end
 # CHECKERR: function ()
 # CHECKERR: ^
 
+# Tests the --argument-names and --inherit-variable can overwrite argv
+function t --argument-names a argv c
+    echo $argv
+end
+t 1 2 3
+#CHECK: 2
+
+function t -a argv
+    echo $argv
+end
+t 1 2 3
+#CHECK: 1
+
+function outer
+    function inner -v argv -V argv
+        echo $argv
+    end
+    set -gx argv 4 5 6
+end
+outer 1 2 3
+#CHECK: 1 2 3
+
 exit 0