fix!: Only apply num_args to user values

CHANGELOG.md

@@ -23,6 +23,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Replace `Arg::number_of_values` (average across occurrences) with `Arg::num_args` (per occurrence, raw CLI args, not parsed values)
   - `num_args(0)` no longer implies `takes_value(true).multiple_values(true)`
   - `num_args(1)` no longer implies `multiple_values(true)`
+  - Does not check default values, only what the user explicitly passes in
+- Sometimes `Arg::default_missing_value` didn't require `num_args(0..=1)`, now it does
 - Replace `Arg::min_values` (across all occurrences) with `Arg::num_args(N..)` (per occurrence)
 - Replace `Arg::max_values` (across all occurrences) with `Arg::num_args(1..=M)` (per occurrence)
 - Replace `Arg::multiple_values(true)` with `Arg::num_args(1..)` and `Arg::multiple_values(false)` with `Arg::num_args(0)`

src/parser/parser.rs

@@ -1127,6 +1127,10 @@ impl<'help, 'cmd> Parser<'help, 'cmd> {
             ident,
             source
         );
+
+        // `default_missing_values` does not count (ie to avoid problems with flags)
+        self.verify_num_args(arg, &raw_vals)?;
+
         if raw_vals.is_empty() {
             // We assume this case is valid: require equals, but min_vals == 0.
             if !arg.default_missing_vals.is_empty() {
@@ -1148,8 +1152,6 @@ impl<'help, 'cmd> Parser<'help, 'cmd> {
             };
         }
 
-        self.verify_num_args(arg, &raw_vals)?;
-
         match arg.get_action() {
             ArgAction::Set => {
                 if source == ValueSource::CommandLine

tests/builder/default_missing_vals.rs

@@ -171,6 +171,7 @@ fn default_missing_value_flag_value() {
         Arg::new("flag")
             .long("flag")
             .action(ArgAction::Set)
+            .num_args(0..=1)
             .default_value("false")
             .default_missing_value("true"),
     );

tests/builder/default_vals.rs

@@ -874,6 +874,7 @@ fn missing_with_value_delimiter() {
         Arg::new("option")
             .long("option")
             .value_delimiter(';')
+            .num_args(0..=1)
             .default_missing_values(&["value1;value2;value3", "value4;value5"]),
     );