WIP: add from_env option

src/app/help.rs

@@ -474,6 +474,7 @@ impl<'a> Help<'a> {
                                            Format::None(pv.to_string_lossy())
                                        }));
             }
+            // FIXME: add [env::{}: {}] here
         }
         if let Some(ref aliases) = a.aliases() {
             debugln!("Help::spec_vals: Found aliases...{:?}", aliases);

src/app/mod.rs

@@ -1796,6 +1796,7 @@ impl<'n, 'e> AnyArg<'n, 'e> for App<'n, 'e> {
     fn default_vals_ifs(&self) -> Option<map::Values<(&'n str, Option<&'e OsStr>, &'e OsStr)>> {
         None
     }
+    fn from_env(&self) -> Option<&OsString> { None }
     fn longest_filter(&self) -> bool { true }
     fn aliases(&self) -> Option<Vec<&'e str>> {
         if let Some(ref aliases) = self.p.meta.aliases {

src/app/parser.rs

@@ -1789,6 +1789,38 @@ impl<'a, 'b> Parser<'a, 'b>
         Ok(())
     }
     
+    pub fn add_from_env(&mut self, matcher: &mut ArgMatcher<'a>) -> ClapResult<()> {
+        macro_rules! add_val {
+            ($_self:ident, $a:ident, $m:ident) => {
+                if let Some(ref val) = $a.v.from_env {
+                    if $m.get($a.b.name).map(|ma| ma.vals.len()).map(|len| len == 0).unwrap_or(false) {
+                        $_self.add_val_to_arg($a, OsStr::new(val), $m)?;
+
+                        if $_self.cache.map_or(true, |name| name != $a.name()) {
+                            arg_post_processing!($_self, $a, $m);
+                            $_self.cache = Some($a.name());
+                        }
+                    } else {
+                        $_self.add_val_to_arg($a, OsStr::new(val), $m)?;
+
+                        if $_self.cache.map_or(true, |name| name != $a.name()) {
+                            arg_post_processing!($_self, $a, $m);
+                            $_self.cache = Some($a.name());
+                        }
+                    }
+                }
+            };
+        }
+
+        for o in &self.opts {
+            add_val!(self, o, matcher);
+        }
+        for p in self.positionals.values() {
+            add_val!(self, p, matcher);
+        }
+        Ok(())
+    }
+
     pub fn flags(&self) -> Iter<FlagBuilder<'a, 'b>> { self.flags.iter() }
 
     pub fn opts(&self) -> Iter<OptBuilder<'a, 'b>> { self.opts.iter() }

src/app/validator.rs

@@ -28,6 +28,7 @@ impl<'a, 'b, 'z> Validator<'a, 'b, 'z> {
                     -> ClapResult<()> {
         debugln!("Validator::validate;");
         let mut reqs_validated = false;
+        self.0.add_from_env(matcher)?;
         self.0.add_defaults(matcher)?;
         if let ParseResult::Opt(a) = needs_val_of {
             debugln!("Validator::validate: needs_val_of={:?}", a);

src/args/any_arg.rs

@@ -33,6 +33,7 @@ pub trait AnyArg<'n, 'e>: std_fmt::Display {
     fn long_help(&self) -> Option<&'e str>;
     fn default_val(&self) -> Option<&'e OsStr>;
     fn default_vals_ifs(&self) -> Option<map::Values<(&'n str, Option<&'e OsStr>, &'e OsStr)>>;
+    fn from_env(&self) -> Option<&OsString>;
     fn longest_filter(&self) -> bool;
     fn val_terminator(&self) -> Option<&'e str>;
 }

src/args/arg.rs

@@ -6,7 +6,7 @@ use std::ffi::{OsString, OsStr};
 use osstringext::OsStrExt3;
 #[cfg(not(target_os="windows"))]
 use std::os::unix::ffi::OsStrExt;
-
+use std::env;
 
 #[cfg(feature = "yaml")]
 use yaml_rust::Yaml;
@@ -128,6 +128,7 @@ impl<'a, 'b> Arg<'a, 'b> {
                 "default_value" => yaml_to_str!(a, v, default_value),
                 "default_value_if" => yaml_tuple3!(a, v, default_value_if),
                 "default_value_ifs" => yaml_tuple3!(a, v, default_value_if),
+                "from_env" => yaml_to_str!(a, v, from_env),
                 "value_names" => yaml_vec_or_str!(v, a, value_name),
                 "groups" => yaml_vec_or_str!(v, a, group),
                 "requires" => yaml_vec_or_str!(v, a, requires),
@@ -3311,6 +3312,16 @@ impl<'a, 'b> Arg<'a, 'b> {
         self
     }
 
+    /// Specifies that if the value is not passed in as an argument, that it should be retrieved
+    /// from the environment if available. If it is not present in the environment, then default
+    /// rules will apply.
+    pub fn from_env<K: AsRef<OsStr>>(mut self, name: K) -> Self {
+        self.setb(ArgSettings::TakesValue);
+
+        self.v.from_env = env::var_os(name);
+        self
+    }
+
     /// When set to `true` the help string will be displayed on the line after the argument and
     /// indented once. This can be helpful for arguments with very long or complex help messages.
     /// This can also be helpful for arguments with very long flag names, or many/long value names.

src/args/arg_builder/flag.rs

@@ -8,20 +8,26 @@ use std::mem;
 
 // Internal
 use Arg;
-use args::{ArgSettings, Base, Switched, AnyArg, DispOrder};
+use args::{AnyArg, ArgSettings, Base, DispOrder, Switched};
 use map::{self, VecMap};
 
 #[derive(Default, Clone, Debug)]
 #[doc(hidden)]
 pub struct FlagBuilder<'n, 'e>
-    where 'n: 'e
+where
+    'n: 'e,
 {
     pub b: Base<'n, 'e>,
     pub s: Switched<'e>,
 }
 
 impl<'n, 'e> FlagBuilder<'n, 'e> {
-    pub fn new(name: &'n str) -> Self { FlagBuilder { b: Base::new(name), ..Default::default() } }
+    pub fn new(name: &'n str) -> Self {
+        FlagBuilder {
+            b: Base::new(name),
+            ..Default::default()
+        }
+    }
 }
 
 impl<'a, 'b, 'z> From<&'z Arg<'a, 'b>> for FlagBuilder<'a, 'b> {
@@ -83,10 +89,12 @@ impl<'n, 'e> AnyArg<'n, 'e> for FlagBuilder<'n, 'e> {
     fn default_vals_ifs(&self) -> Option<map::Values<(&'n str, Option<&'e OsStr>, &'e OsStr)>> {
         None
     }
+    fn from_env(&self) -> Option<&OsString> { None }
     fn longest_filter(&self) -> bool { self.s.long.is_some() }
     fn aliases(&self) -> Option<Vec<&'e str>> {
         if let Some(ref aliases) = self.s.aliases {
-            let vis_aliases: Vec<_> = aliases.iter()
+            let vis_aliases: Vec<_> = aliases
+                .iter()
                 .filter_map(|&(n, v)| if v { Some(n) } else { None })
                 .collect();
             if vis_aliases.is_empty() {
@@ -105,9 +113,7 @@ impl<'n, 'e> DispOrder for FlagBuilder<'n, 'e> {
 }
 
 impl<'n, 'e> PartialEq for FlagBuilder<'n, 'e> {
-    fn eq(&self, other: &FlagBuilder<'n, 'e>) -> bool {
+    fn eq(&self, other: &FlagBuilder<'n, 'e>) -> bool { self.b == other.b }
-        self.b == other.b
-    }
 }
 
 #[cfg(test)]
@@ -142,8 +148,12 @@ mod test {
     fn flagbuilder_display_multiple_aliases() {
         let mut f = FlagBuilder::new("flg");
         f.s.short = Some('f');
-        f.s.aliases =
+        f.s.aliases = Some(vec![
-            Some(vec![("alias_not_visible", false), ("f2", true), ("f3", true), ("f4", true)]);
+            ("alias_not_visible", false),
+            ("f2", true),
+            ("f3", true),
+            ("f4", true),
+        ]);
         assert_eq!(&*format!("{}", f), "-f");
     }
 }

src/args/arg_builder/option.rs

@@ -6,14 +6,15 @@ use std::ffi::{OsStr, OsString};
 use std::mem;
 
 // Internal
-use args::{ArgSettings, AnyArg, Base, Switched, Valued, Arg, DispOrder};
+use args::{AnyArg, Arg, ArgSettings, Base, DispOrder, Switched, Valued};
 use map::{self, VecMap};
 
 #[allow(missing_debug_implementations)]
 #[doc(hidden)]
 #[derive(Default, Clone)]
 pub struct OptBuilder<'n, 'e>
-    where 'n: 'e
+where
+    'n: 'e,
 {
     pub b: Base<'n, 'e>,
     pub s: Switched<'e>,
@@ -21,7 +22,12 @@ pub struct OptBuilder<'n, 'e>
 }
 
 impl<'n, 'e> OptBuilder<'n, 'e> {
-    pub fn new(name: &'n str) -> Self { OptBuilder { b: Base::new(name), ..Default::default() } }
+    pub fn new(name: &'n str) -> Self {
+        OptBuilder {
+            b: Base::new(name),
+            ..Default::default()
+        }
+    }
 }
 
 impl<'n, 'e, 'z> From<&'z Arg<'n, 'e>> for OptBuilder<'n, 'e> {
@@ -85,14 +91,16 @@ impl<'n, 'e> Display for OptBuilder<'n, 'e> {
                 write!(f, "...")?;
             }
         } else {
-            write!(f,
+            write!(
+                f,
                 "<{}>{}",
                 self.b.name,
                 if self.is_set(ArgSettings::Multiple) {
                     "..."
                 } else {
                     ""
-                })?;
+                }
+            )?;
         }
 
         Ok(())
@@ -132,10 +140,12 @@ impl<'n, 'e> AnyArg<'n, 'e> for OptBuilder<'n, 'e> {
     fn default_vals_ifs(&self) -> Option<map::Values<(&'n str, Option<&'e OsStr>, &'e OsStr)>> {
         self.v.default_vals_ifs.as_ref().map(|vm| vm.values())
     }
+    fn from_env(&self) -> Option<&OsString> { self.v.from_env.as_ref() }
     fn longest_filter(&self) -> bool { true }
     fn aliases(&self) -> Option<Vec<&'e str>> {
         if let Some(ref aliases) = self.s.aliases {
-            let vis_aliases: Vec<_> = aliases.iter()
+            let vis_aliases: Vec<_> = aliases
+                .iter()
                 .filter_map(|&(n, v)| if v { Some(n) } else { None })
                 .collect();
             if vis_aliases.is_empty() {
@@ -154,9 +164,7 @@ impl<'n, 'e> DispOrder for OptBuilder<'n, 'e> {
 }
 
 impl<'n, 'e> PartialEq for OptBuilder<'n, 'e> {
-    fn eq(&self, other: &OptBuilder<'n, 'e>) -> bool {
+    fn eq(&self, other: &OptBuilder<'n, 'e>) -> bool { self.b == other.b }
-        self.b == other.b
-    }
 }
 
 #[cfg(test)]
@@ -214,8 +222,12 @@ mod test {
     fn optbuilder_display_multiple_aliases() {
         let mut o = OptBuilder::new("opt");
         o.s.long = Some("option");
-        o.s.aliases =
+        o.s.aliases = Some(vec![
-            Some(vec![("als_not_visible", false), ("als2", true), ("als3", true), ("als4", true)]);
+            ("als_not_visible", false),
+            ("als2", true),
+            ("als3", true),
+            ("als4", true),
+        ]);
         assert_eq!(&*format!("{}", o), "--option <opt>");
     }
 }

src/args/arg_builder/positional.rs

@@ -8,7 +8,7 @@ use std::mem;
 
 // Internal
 use Arg;
-use args::{ArgSettings, Base, Valued, AnyArg, DispOrder};
+use args::{AnyArg, ArgSettings, Base, DispOrder, Valued};
 use INTERNAL_ERROR_MSG;
 use map::{self, VecMap};
 
@@ -16,7 +16,8 @@ use map::{self, VecMap};
 #[doc(hidden)]
 #[derive(Clone, Default)]
 pub struct PosBuilder<'n, 'e>
-    where 'n: 'e
+where
+    'n: 'e,
 {
     pub b: Base<'n, 'e>,
     pub v: Valued<'n, 'e>,
@@ -39,7 +40,8 @@ impl<'n, 'e> PosBuilder<'n, 'e> {
             index: idx,
         };
         if a.v.max_vals.is_some() || a.v.min_vals.is_some() ||
-           (a.v.num_vals.is_some() && a.v.num_vals.unwrap() > 1) {
+            (a.v.num_vals.is_some() && a.v.num_vals.unwrap() > 1)
+        {
             pb.b.settings.set(ArgSettings::Multiple);
         }
         pb
@@ -47,7 +49,8 @@ impl<'n, 'e> PosBuilder<'n, 'e> {
 
     pub fn from_arg(mut a: Arg<'n, 'e>, idx: u64) -> Self {
         if a.v.max_vals.is_some() || a.v.min_vals.is_some() ||
-           (a.v.num_vals.is_some() && a.v.num_vals.unwrap() > 1) {
+            (a.v.num_vals.is_some() && a.v.num_vals.unwrap() > 1)
+        {
             a.b.settings.set(ArgSettings::Multiple);
         }
         PosBuilder {
@@ -74,11 +77,13 @@ impl<'n, 'e> PosBuilder<'n, 'e> {
         if let Some(ref names) = self.v.val_names {
             debugln!("PosBuilder:name_no_brackets: val_names={:#?}", names);
             if names.len() > 1 {
-                Cow::Owned(names
+                Cow::Owned(
+                    names
                         .values()
                         .map(|n| format!("<{}>", n))
                         .collect::<Vec<_>>()
-                               .join(" "))
+                        .join(" "),
+                )
             } else {
                 Cow::Borrowed(names.values().next().expect(INTERNAL_ERROR_MSG))
             }
@@ -92,17 +97,21 @@ impl<'n, 'e> PosBuilder<'n, 'e> {
 impl<'n, 'e> Display for PosBuilder<'n, 'e> {
     fn fmt(&self, f: &mut Formatter) -> Result {
         if let Some(ref names) = self.v.val_names {
-            write!(f,
+            write!(
+                f,
                 "{}",
                 names
                     .values()
                     .map(|n| format!("<{}>", n))
                     .collect::<Vec<_>>()
-                    .join(" "))?;
+                    .join(" ")
+            )?;
         } else {
             write!(f, "<{}>", self.b.name)?;
         }
-        if self.b.settings.is_set(ArgSettings::Multiple) && (self.v.val_names.is_none() || self.v.val_names.as_ref().unwrap().len() == 1) {
+        if self.b.settings.is_set(ArgSettings::Multiple) &&
+            (self.v.val_names.is_none() || self.v.val_names.as_ref().unwrap().len() == 1)
+        {
             write!(f, "...")?;
         }
 
@@ -143,6 +152,7 @@ impl<'n, 'e> AnyArg<'n, 'e> for PosBuilder<'n, 'e> {
         self.v.default_vals_ifs.as_ref().map(|vm| vm.values())
     }
     fn default_val(&self) -> Option<&'e OsStr> { self.v.default_val }
+    fn from_env(&self) -> Option<&OsString> { self.v.from_env.as_ref() }
     fn longest_filter(&self) -> bool { true }
     fn aliases(&self) -> Option<Vec<&'e str>> { None }
 }

src/args/arg_builder/valued.rs

@@ -8,7 +8,8 @@ use Arg;
 #[allow(missing_debug_implementations)]
 #[derive(Clone)]
 pub struct Valued<'a, 'b>
-    where 'a: 'b
+where
+    'a: 'b,
 {
     pub possible_vals: Option<Vec<&'b str>>,
     pub val_names: Option<VecMap<&'b str>>,
@@ -20,6 +21,7 @@ pub struct Valued<'a, 'b>
     pub val_delim: Option<char>,
     pub default_val: Option<&'b OsStr>,
     pub default_vals_ifs: Option<VecMap<(&'a str, Option<&'b OsStr>, &'b OsStr)>>,
+    pub from_env: Option<OsString>,
     pub terminator: Option<&'b str>,
 }
 
@@ -36,6 +38,7 @@ impl<'n, 'e> Default for Valued<'n, 'e> {
             val_delim: None,
             default_val: None,
             default_vals_ifs: None,
+            from_env: None,
             terminator: None,
         }
     }

tests/default_vals.rs

@@ -8,8 +8,9 @@ use clap::{App, Arg, ErrorKind};
 #[test]
 fn opts() {
     let r = App::new("df")
-        .arg( Arg::from_usage("-o [opt] 'some opt'")
+        .arg(
-            .default_value("default"))
+            Arg::from_usage("-o [opt] 'some opt'").default_value("default"),
+        )
         .get_matches_from_safe(vec![""]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -20,8 +21,9 @@ fn opts() {
 #[test]
 fn opt_user_override() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'")
+        .arg(
-            .default_value("default"))
+            Arg::from_usage("--opt [FILE] 'some arg'").default_value("default"),
+        )
         .get_matches_from_safe(vec!["", "--opt", "value"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -32,8 +34,7 @@ fn opt_user_override() {
 #[test]
 fn positionals() {
     let r = App::new("df")
-        .arg( Arg::from_usage("[arg] 'some opt'")
+        .arg(Arg::from_usage("[arg] 'some opt'").default_value("default"))
-            .default_value("default"))
         .get_matches_from_safe(vec![""]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -44,8 +45,7 @@ fn positionals() {
 #[test]
 fn positional_user_override() {
     let r = App::new("df")
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(Arg::from_usage("[arg] 'some arg'").default_value("default"))
-            .default_value("default"))
         .get_matches_from_safe(vec!["", "value"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -61,8 +61,9 @@ fn osstr_opts() {
     let expected = OsStr::new("default");
 
     let r = App::new("df")
-        .arg( Arg::from_usage("-o [opt] 'some opt'")
+        .arg(
-            .default_value_os(expected))
+            Arg::from_usage("-o [opt] 'some opt'").default_value_os(expected),
+        )
         .get_matches_from_safe(vec![""]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -76,8 +77,9 @@ fn osstr_opt_user_override() {
     let default = OsStr::new("default");
 
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'")
+        .arg(
-            .default_value_os(default))
+            Arg::from_usage("--opt [FILE] 'some arg'").default_value_os(default),
+        )
         .get_matches_from_safe(vec!["", "--opt", "value"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -91,8 +93,9 @@ fn osstr_positionals() {
     let expected = OsStr::new("default");
 
     let r = App::new("df")
-        .arg( Arg::from_usage("[arg] 'some opt'")
+        .arg(
-            .default_value_os(expected))
+            Arg::from_usage("[arg] 'some opt'").default_value_os(expected),
+        )
         .get_matches_from_safe(vec![""]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -106,8 +109,9 @@ fn osstr_positional_user_override() {
     let default = OsStr::new("default");
 
     let r = App::new("df")
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
-            .default_value_os(default))
+            Arg::from_usage("[arg] 'some arg'").default_value_os(default),
+        )
         .get_matches_from_safe(vec!["", "value"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -120,9 +124,12 @@ fn osstr_positional_user_override() {
 #[test]
 fn default_if_arg_present_no_default() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(Arg::from_usage("[arg] 'some arg'").default_value_if(
-            .default_value_if("opt", None, "default"))
+            "opt",
+            None,
+            "default",
+        ))
         .get_matches_from_safe(vec!["", "--opt", "some"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -133,9 +140,12 @@ fn default_if_arg_present_no_default() {
 #[test]
 fn default_if_arg_present_no_default_user_override() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(Arg::from_usage("[arg] 'some arg'").default_value_if(
-            .default_value_if("opt", None, "default"))
+            "opt",
+            None,
+            "default",
+        ))
         .get_matches_from_safe(vec!["", "--opt", "some", "other"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -146,10 +156,12 @@ fn default_if_arg_present_no_default_user_override() {
 #[test]
 fn default_if_arg_present_no_arg_with_default() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
+            Arg::from_usage("[arg] 'some arg'")
                 .default_value("first")
-            .default_value_if("opt", None, "default"))
+                .default_value_if("opt", None, "default"),
+        )
         .get_matches_from_safe(vec![""]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -160,10 +172,12 @@ fn default_if_arg_present_no_arg_with_default() {
 #[test]
 fn default_if_arg_present_with_default() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
+            Arg::from_usage("[arg] 'some arg'")
                 .default_value("first")
-            .default_value_if("opt", None, "default"))
+                .default_value_if("opt", None, "default"),
+        )
         .get_matches_from_safe(vec!["", "--opt", "some"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -174,10 +188,12 @@ fn default_if_arg_present_with_default() {
 #[test]
 fn default_if_arg_present_with_default_user_override() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
+            Arg::from_usage("[arg] 'some arg'")
                 .default_value("first")
-            .default_value_if("opt", None, "default"))
+                .default_value_if("opt", None, "default"),
+        )
         .get_matches_from_safe(vec!["", "--opt", "some", "other"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -188,10 +204,12 @@ fn default_if_arg_present_with_default_user_override() {
 #[test]
 fn default_if_arg_present_no_arg_with_default_user_override() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
+            Arg::from_usage("[arg] 'some arg'")
                 .default_value("first")
-            .default_value_if("opt", None, "default"))
+                .default_value_if("opt", None, "default"),
+        )
         .get_matches_from_safe(vec!["", "other"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -204,9 +222,12 @@ fn default_if_arg_present_no_arg_with_default_user_override() {
 #[test]
 fn default_if_arg_present_with_value_no_default() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(Arg::from_usage("[arg] 'some arg'").default_value_if(
-            .default_value_if("opt", Some("value"), "default"))
+            "opt",
+            Some("value"),
+            "default",
+        ))
         .get_matches_from_safe(vec!["", "--opt", "value"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -217,9 +238,12 @@ fn default_if_arg_present_with_value_no_default() {
 #[test]
 fn default_if_arg_present_with_value_no_default_fail() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(Arg::from_usage("[arg] 'some arg'").default_value_if(
-            .default_value_if("opt", Some("value"), "default"))
+            "opt",
+            Some("value"),
+            "default",
+        ))
         .get_matches_from_safe(vec!["", "--opt", "other"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -230,9 +254,12 @@ fn default_if_arg_present_with_value_no_default_fail() {
 #[test]
 fn default_if_arg_present_with_value_no_default_user_override() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(Arg::from_usage("[arg] 'some arg'").default_value_if(
-            .default_value_if("opt", Some("some"), "default"))
+            "opt",
+            Some("some"),
+            "default",
+        ))
         .get_matches_from_safe(vec!["", "--opt", "some", "other"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -243,10 +270,12 @@ fn default_if_arg_present_with_value_no_default_user_override() {
 #[test]
 fn default_if_arg_present_with_value_no_arg_with_default() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
+            Arg::from_usage("[arg] 'some arg'")
                 .default_value("first")
-            .default_value_if("opt", Some("some"), "default"))
+                .default_value_if("opt", Some("some"), "default"),
+        )
         .get_matches_from_safe(vec![""]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -257,10 +286,12 @@ fn default_if_arg_present_with_value_no_arg_with_default() {
 #[test]
 fn default_if_arg_present_with_value_no_arg_with_default_fail() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
+            Arg::from_usage("[arg] 'some arg'")
                 .default_value("first")
-            .default_value_if("opt", Some("some"), "default"))
+                .default_value_if("opt", Some("some"), "default"),
+        )
         .get_matches_from_safe(vec!["", "--opt", "other"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -271,10 +302,12 @@ fn default_if_arg_present_with_value_no_arg_with_default_fail() {
 #[test]
 fn default_if_arg_present_with_value_with_default() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
+            Arg::from_usage("[arg] 'some arg'")
                 .default_value("first")
-            .default_value_if("opt", Some("some"), "default"))
+                .default_value_if("opt", Some("some"), "default"),
+        )
         .get_matches_from_safe(vec!["", "--opt", "some"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -285,10 +318,12 @@ fn default_if_arg_present_with_value_with_default() {
 #[test]
 fn default_if_arg_present_with_value_with_default_user_override() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
+            Arg::from_usage("[arg] 'some arg'")
                 .default_value("first")
-            .default_value_if("opt", Some("some"), "default"))
+                .default_value_if("opt", Some("some"), "default"),
+        )
         .get_matches_from_safe(vec!["", "--opt", "some", "other"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -299,10 +334,12 @@ fn default_if_arg_present_with_value_with_default_user_override() {
 #[test]
 fn default_if_arg_present_no_arg_with_value_with_default_user_override() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
+            Arg::from_usage("[arg] 'some arg'")
                 .default_value("first")
-            .default_value_if("opt", Some("some"), "default"))
+                .default_value_if("opt", Some("some"), "default"),
+        )
         .get_matches_from_safe(vec!["", "other"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -313,10 +350,12 @@ fn default_if_arg_present_no_arg_with_value_with_default_user_override() {
 #[test]
 fn default_if_arg_present_no_arg_with_value_with_default_user_override_fail() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
+            Arg::from_usage("[arg] 'some arg'")
                 .default_value("first")
-            .default_value_if("opt", Some("some"), "default"))
+                .default_value_if("opt", Some("some"), "default"),
+        )
         .get_matches_from_safe(vec!["", "--opt", "value", "other"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -329,14 +368,13 @@ fn default_if_arg_present_no_arg_with_value_with_default_user_override_fail() {
 #[test]
 fn default_ifs_arg_present() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("--flag 'some arg'"))
+        .arg(Arg::from_usage("--flag 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
+            Arg::from_usage("[arg] 'some arg'")
                 .default_value("first")
-            .default_value_ifs(&[
+                .default_value_ifs(&[("opt", Some("some"), "default"), ("flag", None, "flg")]),
-                ("opt", Some("some"), "default"),
+        )
-                ("flag", None, "flg"),
-            ]))
         .get_matches_from_safe(vec!["", "--flag"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -347,14 +385,13 @@ fn default_ifs_arg_present() {
 #[test]
 fn default_ifs_arg_present_user_override() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("--flag 'some arg'"))
+        .arg(Arg::from_usage("--flag 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
+            Arg::from_usage("[arg] 'some arg'")
                 .default_value("first")
-            .default_value_ifs(&[
+                .default_value_ifs(&[("opt", Some("some"), "default"), ("flag", None, "flg")]),
-                ("opt", Some("some"), "default"),
+        )
-                ("flag", None, "flg"),
-            ]))
         .get_matches_from_safe(vec!["", "--flag", "value"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -365,14 +402,13 @@ fn default_ifs_arg_present_user_override() {
 #[test]
 fn default_ifs_arg_present_order() {
     let r = App::new("df")
-        .arg( Arg::from_usage("--opt [FILE] 'some arg'"))
+        .arg(Arg::from_usage("--opt [FILE] 'some arg'"))
-        .arg( Arg::from_usage("--flag 'some arg'"))
+        .arg(Arg::from_usage("--flag 'some arg'"))
-        .arg( Arg::from_usage("[arg] 'some arg'")
+        .arg(
+            Arg::from_usage("[arg] 'some arg'")
                 .default_value("first")
-            .default_value_ifs(&[
+                .default_value_ifs(&[("opt", Some("some"), "default"), ("flag", None, "flg")]),
-                ("opt", Some("some"), "default"),
+        )
-                ("flag", None, "flg"),
-            ]))
         .get_matches_from_safe(vec!["", "--opt=some", "--flag"]);
     assert!(r.is_ok());
     let m = r.unwrap();
@@ -386,19 +422,25 @@ fn conditional_reqs_fail() {
         .version("1.0")
         .author("F0x06")
         .about("Arg test")
-        .arg(Arg::with_name("target")
+        .arg(
+            Arg::with_name("target")
                 .takes_value(true)
                 .default_value("file")
                 .possible_values(&["file", "stdout"])
-            .long("target"))
+                .long("target"),
-        .arg(Arg::with_name("input")
+        )
+        .arg(
+            Arg::with_name("input")
                 .takes_value(true)
                 .required(true)
-            .long("input"))
+                .long("input"),
-        .arg(Arg::with_name("output")
+        )
+        .arg(
+            Arg::with_name("output")
                 .takes_value(true)
                 .required_if("target", "file")
-            .long("output"))
+                .long("output"),
+        )
         .get_matches_from_safe(vec!["test", "--input", "some"]);
 
     assert!(m.is_err());
@@ -411,19 +453,25 @@ fn conditional_reqs_pass() {
         .version("1.0")
         .author("F0x06")
         .about("Arg test")
-        .arg(Arg::with_name("target")
+        .arg(
+            Arg::with_name("target")
                 .takes_value(true)
                 .default_value("file")
                 .possible_values(&["file", "stdout"])
-            .long("target"))
+                .long("target"),
-        .arg(Arg::with_name("input")
+        )
+        .arg(
+            Arg::with_name("input")
                 .takes_value(true)
                 .required(true)
-            .long("input"))
+                .long("input"),
-        .arg(Arg::with_name("output")
+        )
+        .arg(
+            Arg::with_name("output")
                 .takes_value(true)
                 .required_if("target", "file")
-            .long("output"))
+                .long("output"),
+        )
         .get_matches_from_safe(vec!["test", "--input", "some", "--output", "other"]);
 
     assert!(m.is_ok());
@@ -431,3 +479,16 @@ fn conditional_reqs_pass() {
     assert_eq!(m.value_of("output"), Some("other"));
     assert_eq!(m.value_of("input"), Some("some"));
 }
+
+#[test]
+fn from_env_no_default() {
+    std::env::set_var("CLP_TEST_ENV", "from_env");
+
+    let r = App::new("df")
+        .arg(Arg::from_usage("[arg] 'some opt'").from_env("CLP_TEST_ENV"))
+        .get_matches_from_safe(vec![""]);
+    assert!(r.is_ok());
+    let m = r.unwrap();
+    // assert!(m.is_present("arg")); // TODO: should this be true?
+    assert_eq!(m.value_of("arg").unwrap(), "from_env");
+}