diff --git a/src/build/app/mod.rs b/src/build/app.rs
similarity index 99%
rename from src/build/app/mod.rs
rename to src/build/app.rs
index b63621eb250..77c87ebd413 100644
--- a/src/build/app/mod.rs
+++ b/src/build/app.rs
@@ -1,11 +1,3 @@
-#[cfg(debug_assertions)]
-mod debug_asserts;
-mod settings;
-#[cfg(test)]
-mod tests;
-
-pub use self::settings::{AppFlags, AppSettings};
-
 // Std
 use std::{
     collections::HashMap,
@@ -23,6 +15,7 @@ use os_str_bytes::RawOsStr;
 use yaml_rust::Yaml;
 
 // Internal
+use crate::build::app_settings::{AppFlags, AppSettings};
 use crate::build::{arg::ArgProvider, Arg, ArgGroup, ArgPredicate};
 use crate::error::ErrorKind;
 use crate::error::Result as ClapResult;
@@ -32,6 +25,9 @@ use crate::parse::{ArgMatcher, ArgMatches, Input, Parser};
 use crate::util::{color::ColorChoice, Id, Key};
 use crate::{Error, INTERNAL_ERROR_MSG};
 
+#[cfg(debug_assertions)]
+use crate::build::debug_asserts::assert_app;
+
 /// Build a command-line interface.
 ///
 /// This includes defining arguments, subcommands, parser behavior, and help output.
@@ -2802,14 +2798,14 @@ impl<'help> App<'help> {
             self.args._build();
 
             #[cfg(debug_assertions)]
-            self::debug_asserts::assert_app(self);
+            assert_app(self);
             self.settings.set(AppSettings::Built);
         } else {
             debug!("App::_build: already built");
         }
     }
 
-    fn _panic_on_missing_help(&self, help_required_globally: bool) {
+    pub(crate) fn _panic_on_missing_help(&self, help_required_globally: bool) {
         if self.is_set(AppSettings::HelpExpected) || help_required_globally {
             let args_missing_help: Vec<String> = self
                 .args
@@ -2831,7 +2827,7 @@ impl<'help> App<'help> {
     }
 
     #[cfg(debug_assertions)]
-    fn two_args_of<F>(&self, condition: F) -> Option<(&Arg<'help>, &Arg<'help>)>
+    pub(crate) fn two_args_of<F>(&self, condition: F) -> Option<(&Arg<'help>, &Arg<'help>)>
     where
         F: Fn(&Arg) -> bool,
     {
diff --git a/src/build/app/settings.rs b/src/build/app_settings.rs
similarity index 100%
rename from src/build/app/settings.rs
rename to src/build/app_settings.rs
diff --git a/src/build/app/tests.rs b/src/build/app_tests.rs
similarity index 100%
rename from src/build/app/tests.rs
rename to src/build/app_tests.rs
diff --git a/src/build/arg/mod.rs b/src/build/arg.rs
similarity index 99%
rename from src/build/arg/mod.rs
rename to src/build/arg.rs
index 0de3dba9a5c..fd0f81a60d1 100644
--- a/src/build/arg/mod.rs
+++ b/src/build/arg.rs
@@ -1,17 +1,3 @@
-mod arg_predicate;
-#[cfg(debug_assertions)]
-pub mod debug_asserts;
-mod possible_value;
-mod settings;
-#[cfg(test)]
-mod tests;
-mod value_hint;
-
-pub use self::possible_value::PossibleValue;
-pub use self::settings::{ArgFlags, ArgSettings};
-pub use self::value_hint::ValueHint;
-pub(crate) use arg_predicate::ArgPredicate;
-
 // Std
 use std::{
     borrow::Cow,
@@ -29,17 +15,16 @@ use std::{env, ffi::OsString};
 use yaml_rust::Yaml;
 
 // Internal
-use crate::{
-    build::usage_parser::UsageParser,
-    util::{Id, Key},
-    INTERNAL_ERROR_MSG,
-};
-
-#[cfg(feature = "regex")]
-mod regex;
+use crate::build::usage_parser::UsageParser;
+use crate::build::ArgPredicate;
+use crate::util::{Id, Key};
+use crate::PossibleValue;
+use crate::ValueHint;
+use crate::INTERNAL_ERROR_MSG;
+use crate::{ArgFlags, ArgSettings};
 
 #[cfg(feature = "regex")]
-pub use self::regex::RegexRef;
+use crate::build::RegexRef;
 
 /// The abstract representation of a command line argument. Used to set all the options and
 /// relationships that define a valid argument for the program.
diff --git a/src/build/arg/debug_asserts.rs b/src/build/arg/debug_asserts.rs
deleted file mode 100644
index e4e1e843153..00000000000
--- a/src/build/arg/debug_asserts.rs
+++ /dev/null
@@ -1,135 +0,0 @@
-use crate::{Arg, ValueHint};
-
-pub(crate) fn assert_arg(arg: &Arg) {
-    debug!("Arg::_debug_asserts:{}", arg.name);
-
-    // Self conflict
-    // TODO: this check should be recursive
-    assert!(
-        !arg.blacklist.iter().any(|x| *x == arg.id),
-        "Argument '{}' cannot conflict with itself",
-        arg.name,
-    );
-
-    if arg.value_hint != ValueHint::Unknown {
-        assert!(
-            arg.is_takes_value_set(),
-            "Argument '{}' has value hint but takes no value",
-            arg.name
-        );
-
-        if arg.value_hint == ValueHint::CommandWithArguments {
-            assert!(
-                arg.is_multiple_values_set(),
-                "Argument '{}' uses hint CommandWithArguments and must accept multiple values",
-                arg.name
-            )
-        }
-    }
-
-    if arg.index.is_some() {
-        assert!(
-            arg.is_positional(),
-            "Argument '{}' is a positional argument and can't have short or long name versions",
-            arg.name
-        );
-    }
-
-    if arg.is_required_set() {
-        assert!(
-            arg.default_vals.is_empty(),
-            "Argument '{}' is required and can't have a default value",
-            arg.name
-        );
-    }
-
-    assert_arg_flags(arg);
-
-    assert_defaults(arg, "default_value", arg.default_vals.iter().copied());
-    assert_defaults(
-        arg,
-        "default_missing_value",
-        arg.default_missing_vals.iter().copied(),
-    );
-    assert_defaults(
-        arg,
-        "default_value_if",
-        arg.default_vals_ifs
-            .iter()
-            .filter_map(|(_, _, default)| *default),
-    );
-}
-
-fn assert_arg_flags(arg: &Arg) {
-    macro_rules! checker {
-        ($a:ident requires $($b:ident)|+) => {
-            if arg.$a() {
-                let mut s = String::new();
-
-                $(
-                    if !arg.$b() {
-                        s.push_str(&format!("  Arg::{} is required when Arg::{} is set.\n", std::stringify!($b), std::stringify!($a)));
-                    }
-                )+
-
-                if !s.is_empty() {
-                    panic!("Argument {:?}\n{}", arg.get_name(), s)
-                }
-            }
-        }
-    }
-
-    checker!(is_forbid_empty_values_set requires is_takes_value_set);
-    checker!(is_require_value_delimiter_set requires is_takes_value_set);
-    checker!(is_require_value_delimiter_set requires is_use_value_delimiter_set);
-    checker!(is_hide_possible_values_set requires is_takes_value_set);
-    checker!(is_allow_hyphen_values_set requires is_takes_value_set);
-    checker!(is_require_equals_set requires is_takes_value_set);
-    checker!(is_last_set requires is_takes_value_set);
-    checker!(is_hide_default_value_set requires is_takes_value_set);
-    checker!(is_multiple_values_set requires is_takes_value_set);
-    checker!(is_ignore_case_set requires is_takes_value_set);
-    checker!(is_allow_invalid_utf8_set requires is_takes_value_set);
-}
-
-fn assert_defaults<'d>(
-    arg: &Arg,
-    field: &'static str,
-    defaults: impl IntoIterator<Item = &'d std::ffi::OsStr>,
-) {
-    for default_os in defaults {
-        if let Some(default_s) = default_os.to_str() {
-            if !arg.possible_vals.is_empty() {
-                assert!(
-                    arg.possible_vals.iter().any(|possible_val| {
-                        possible_val.matches(default_s, arg.is_ignore_case_set())
-                    }),
-                    "Argument `{}`'s {}={} doesn't match possible values",
-                    arg.name,
-                    field,
-                    default_s
-                );
-            }
-
-            if let Some(validator) = arg.validator.as_ref() {
-                let mut validator = validator.lock().unwrap();
-                if let Err(err) = validator(default_s) {
-                    panic!(
-                        "Argument `{}`'s {}={} failed validation: {}",
-                        arg.name, field, default_s, err
-                    );
-                }
-            }
-        }
-
-        if let Some(validator) = arg.validator_os.as_ref() {
-            let mut validator = validator.lock().unwrap();
-            if let Err(err) = validator(default_os) {
-                panic!(
-                    "Argument `{}`'s {}={:?} failed validation: {}",
-                    arg.name, field, default_os, err
-                );
-            }
-        }
-    }
-}
diff --git a/src/build/arg/arg_predicate.rs b/src/build/arg_predicate.rs
similarity index 100%
rename from src/build/arg/arg_predicate.rs
rename to src/build/arg_predicate.rs
diff --git a/src/build/arg/settings.rs b/src/build/arg_settings.rs
similarity index 100%
rename from src/build/arg/settings.rs
rename to src/build/arg_settings.rs
diff --git a/src/build/arg/tests.rs b/src/build/arg_tests.rs
similarity index 100%
rename from src/build/arg/tests.rs
rename to src/build/arg_tests.rs
diff --git a/src/build/app/debug_asserts.rs b/src/build/debug_asserts.rs
similarity index 81%
rename from src/build/app/debug_asserts.rs
rename to src/build/debug_asserts.rs
index c3d7a5654d8..185037caea7 100644
--- a/src/build/app/debug_asserts.rs
+++ b/src/build/debug_asserts.rs
@@ -1,11 +1,10 @@
-use crate::{
-    build::arg::{debug_asserts::assert_arg, ArgProvider},
-    mkeymap::KeyType,
-    util::Id,
-    App, AppSettings, Arg, ValueHint,
-};
 use std::cmp::Ordering;
 
+use crate::build::arg::ArgProvider;
+use crate::mkeymap::KeyType;
+use crate::util::Id;
+use crate::{App, AppSettings, Arg, ValueHint};
+
 pub(crate) fn assert_app(app: &App) {
     debug!("App::_debug_asserts");
 
@@ -577,3 +576,137 @@ fn _verify_positionals(app: &App) -> bool {
 
     true
 }
+
+fn assert_arg(arg: &Arg) {
+    debug!("Arg::_debug_asserts:{}", arg.name);
+
+    // Self conflict
+    // TODO: this check should be recursive
+    assert!(
+        !arg.blacklist.iter().any(|x| *x == arg.id),
+        "Argument '{}' cannot conflict with itself",
+        arg.name,
+    );
+
+    if arg.value_hint != ValueHint::Unknown {
+        assert!(
+            arg.is_takes_value_set(),
+            "Argument '{}' has value hint but takes no value",
+            arg.name
+        );
+
+        if arg.value_hint == ValueHint::CommandWithArguments {
+            assert!(
+                arg.is_multiple_values_set(),
+                "Argument '{}' uses hint CommandWithArguments and must accept multiple values",
+                arg.name
+            )
+        }
+    }
+
+    if arg.index.is_some() {
+        assert!(
+            arg.is_positional(),
+            "Argument '{}' is a positional argument and can't have short or long name versions",
+            arg.name
+        );
+    }
+
+    if arg.is_required_set() {
+        assert!(
+            arg.default_vals.is_empty(),
+            "Argument '{}' is required and can't have a default value",
+            arg.name
+        );
+    }
+
+    assert_arg_flags(arg);
+
+    assert_defaults(arg, "default_value", arg.default_vals.iter().copied());
+    assert_defaults(
+        arg,
+        "default_missing_value",
+        arg.default_missing_vals.iter().copied(),
+    );
+    assert_defaults(
+        arg,
+        "default_value_if",
+        arg.default_vals_ifs
+            .iter()
+            .filter_map(|(_, _, default)| *default),
+    );
+}
+
+fn assert_arg_flags(arg: &Arg) {
+    macro_rules! checker {
+        ($a:ident requires $($b:ident)|+) => {
+            if arg.$a() {
+                let mut s = String::new();
+
+                $(
+                    if !arg.$b() {
+                        s.push_str(&format!("  Arg::{} is required when Arg::{} is set.\n", std::stringify!($b), std::stringify!($a)));
+                    }
+                )+
+
+                if !s.is_empty() {
+                    panic!("Argument {:?}\n{}", arg.get_name(), s)
+                }
+            }
+        }
+    }
+
+    checker!(is_forbid_empty_values_set requires is_takes_value_set);
+    checker!(is_require_value_delimiter_set requires is_takes_value_set);
+    checker!(is_require_value_delimiter_set requires is_use_value_delimiter_set);
+    checker!(is_hide_possible_values_set requires is_takes_value_set);
+    checker!(is_allow_hyphen_values_set requires is_takes_value_set);
+    checker!(is_require_equals_set requires is_takes_value_set);
+    checker!(is_last_set requires is_takes_value_set);
+    checker!(is_hide_default_value_set requires is_takes_value_set);
+    checker!(is_multiple_values_set requires is_takes_value_set);
+    checker!(is_ignore_case_set requires is_takes_value_set);
+    checker!(is_allow_invalid_utf8_set requires is_takes_value_set);
+}
+
+fn assert_defaults<'d>(
+    arg: &Arg,
+    field: &'static str,
+    defaults: impl IntoIterator<Item = &'d std::ffi::OsStr>,
+) {
+    for default_os in defaults {
+        if let Some(default_s) = default_os.to_str() {
+            if !arg.possible_vals.is_empty() {
+                assert!(
+                    arg.possible_vals.iter().any(|possible_val| {
+                        possible_val.matches(default_s, arg.is_ignore_case_set())
+                    }),
+                    "Argument `{}`'s {}={} doesn't match possible values",
+                    arg.name,
+                    field,
+                    default_s
+                );
+            }
+
+            if let Some(validator) = arg.validator.as_ref() {
+                let mut validator = validator.lock().unwrap();
+                if let Err(err) = validator(default_s) {
+                    panic!(
+                        "Argument `{}`'s {}={} failed validation: {}",
+                        arg.name, field, default_s, err
+                    );
+                }
+            }
+        }
+
+        if let Some(validator) = arg.validator_os.as_ref() {
+            let mut validator = validator.lock().unwrap();
+            if let Err(err) = validator(default_os) {
+                panic!(
+                    "Argument `{}`'s {}={:?} failed validation: {}",
+                    arg.name, field, default_os, err
+                );
+            }
+        }
+    }
+}
diff --git a/src/build/mod.rs b/src/build/mod.rs
index 3750281069f..06ccb7a8930 100644
--- a/src/build/mod.rs
+++ b/src/build/mod.rs
@@ -4,12 +4,33 @@ mod macros;
 pub mod app;
 pub mod arg;
 
+mod app_settings;
 mod arg_group;
+mod arg_predicate;
+mod arg_settings;
+mod possible_value;
 mod usage_parser;
+mod value_hint;
 
-pub use self::{
-    app::{App, AppFlags, AppSettings},
-    arg::{Arg, ArgFlags, ArgSettings, PossibleValue, ValueHint},
-    arg_group::ArgGroup,
-};
-pub(crate) use arg::ArgPredicate;
+#[cfg(feature = "regex")]
+mod regex;
+
+#[cfg(debug_assertions)]
+mod debug_asserts;
+
+#[cfg(test)]
+mod app_tests;
+#[cfg(test)]
+mod arg_tests;
+
+pub use app::App;
+pub use app_settings::{AppFlags, AppSettings};
+pub use arg::Arg;
+pub use arg_group::ArgGroup;
+pub(crate) use arg_predicate::ArgPredicate;
+pub use arg_settings::{ArgFlags, ArgSettings};
+pub use possible_value::PossibleValue;
+pub use value_hint::ValueHint;
+
+#[cfg(feature = "regex")]
+pub use self::regex::RegexRef;
diff --git a/src/build/arg/possible_value.rs b/src/build/possible_value.rs
similarity index 100%
rename from src/build/arg/possible_value.rs
rename to src/build/possible_value.rs
diff --git a/src/build/arg/regex.rs b/src/build/regex.rs
similarity index 100%
rename from src/build/arg/regex.rs
rename to src/build/regex.rs
diff --git a/src/build/arg/value_hint.rs b/src/build/value_hint.rs
similarity index 100%
rename from src/build/arg/value_hint.rs
rename to src/build/value_hint.rs
diff --git a/src/lib.rs b/src/lib.rs
index 792614fd796..9a48ae8629b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -65,7 +65,7 @@ mod macros;
 mod derive;
 
 #[cfg(feature = "regex")]
-pub use crate::build::arg::RegexRef;
+pub use crate::build::RegexRef;
 
 pub mod error;
 
diff --git a/src/parse/validator.rs b/src/parse/validator.rs
index 4a23c5e8aee..c2694ba4377 100644
--- a/src/parse/validator.rs
+++ b/src/parse/validator.rs
@@ -1,5 +1,5 @@
 // Internal
-use crate::build::{arg::PossibleValue, App, AppSettings as AS, Arg, ArgPredicate};
+use crate::build::{App, AppSettings as AS, Arg, ArgPredicate, PossibleValue};
 use crate::error::{Error, Result as ClapResult};
 use crate::output::Usage;
 use crate::parse::{ArgMatcher, MatchedArg, ParseState, Parser};