Update

src/repository.rs

@@ -1,5 +1,4 @@
-use std::cell::RefCell;
-use std::collections::{HashMap, HashSet};
+use std::collections::HashMap;
 
 use symbols::Symbol;
 use resources::Resource;
@@ -15,11 +14,11 @@ impl<'a, C> SymbolRepository<'a> for C where C: Fn(&Resource) -> Option<Box<Symb
 }
 
 pub struct DispatchingSymbolRepository<'a> {
-  repositories: HashMap<&'static str, Box<SymbolRepository<'a>>>
+  repositories: HashMap<&'a str, Box<SymbolRepository<'a> + 'a>>
 }
 
 impl<'a> DispatchingSymbolRepository<'a> {
-  pub fn new(repositories: HashMap<&'static str, Box<SymbolRepository<'a>>>) -> DispatchingSymbolRepository<'a> {
+  pub fn new(repositories: HashMap<&'a str, Box<SymbolRepository<'a> + 'a>>) -> Self {
     DispatchingSymbolRepository { repositories: repositories }
   }
 }
@@ -29,29 +28,3 @@ impl<'a> SymbolRepository<'a> for DispatchingSymbolRepository<'a> {
     self.repositories.get(resource.get_type()).and_then(|repo| repo.get_symbol(resource))
   }
 }
-
-use std::marker::PhantomData;
-
-pub struct NonRepeatingSymbolRepository<'a, R> where R: SymbolRepository<'a> {
-  upstream: R,
-  done: RefCell<HashSet<Resource>>,
-  d: PhantomData<Box<Symbol + 'a>>
-}
-
-impl<'a, R> NonRepeatingSymbolRepository<'a, R> where R: SymbolRepository<'a> {
-  pub fn new(repository: R) -> Self {
-    NonRepeatingSymbolRepository { upstream: repository, done: RefCell::new(HashSet::new()), d: PhantomData }
-  }
-}
-
-impl<'a, R> SymbolRepository<'a> for NonRepeatingSymbolRepository<'a, R> where R: SymbolRepository<'a> {
-  fn get_symbol(&self, resource: &Resource) -> Option<Box<Symbol + 'a>> {
-    let mut done = self.done.borrow_mut();
-    if done.contains(&resource) {
-      None
-    } else {
-      done.insert(resource.clone());
-      self.upstream.get_symbol(resource)
-    }
-  }
-}

src/schema.rs

@@ -100,15 +100,51 @@ impl<'a, R> SymbolRunner for ReportingSymbolRunner<'a, R> where R: SymbolRunner
   }
 }
 
-pub struct RequirementsResolvingSymbolRunner<'s, R: 's + SymbolRunner, G: 's + SymbolRepository<'s>>(&'s R, &'s G);
+use std::cell::RefCell;
+use std::collections::HashSet;
+use resources::Resource;
 
-impl<'s, R, G> RequirementsResolvingSymbolRunner<'s, R, G> where R: SymbolRunner, G: SymbolRepository<'s> {
-  pub fn new(symbol_runner: &'s R, symbol_repo: &'s G) -> Self {
-    RequirementsResolvingSymbolRunner(symbol_runner, symbol_repo)
+pub struct NonRepeatingSymbolRunner<'a, R> where R: 'a + SymbolRunner {
+  upstream: &'a R,
+  done: RefCell<HashSet<Resource>>
+}
+
+impl<'a, R> NonRepeatingSymbolRunner<'a, R> where R: SymbolRunner {
+  pub fn new(symbol_runner: &'a R) -> Self {
+    NonRepeatingSymbolRunner{ upstream: symbol_runner, done: RefCell::new(HashSet::new()) }
+  }
+}
+
+impl<'a, R> SymbolRunner for NonRepeatingSymbolRunner<'a, R> where R: SymbolRunner {
+  fn run_symbol<S: ?Sized + Symbol + fmt::Display>(&self, logger: &mut Logger, symbol: &S) -> Result<(), Box<Error>>
+  {
+    if let Some(resources) = symbol.provides() {
+      let mut done = self.done.borrow_mut();
+      let mut has_to_run = false;
+      for resource in resources {
+        if !done.contains(&resource) {
+          has_to_run = true;
+          done.insert(resource.clone());
+        }
+      }
+      if !has_to_run {
+        return Ok(());
+      }
+    }
+    self.upstream.run_symbol(logger, &*symbol)
+  }
+}
+use std::marker::PhantomData;
+
+pub struct RequirementsResolvingSymbolRunner<'a, 's, R: 'a + SymbolRunner, G: 'a + SymbolRepository<'s>>(&'a R, &'a G, PhantomData<Box<Symbol + 's>>);
+
+impl<'a, 's, R, G> RequirementsResolvingSymbolRunner<'a, 's, R, G> where R: SymbolRunner, G: SymbolRepository<'s> {
+  pub fn new(symbol_runner: &'a R, symbol_repo: &'a G) -> Self {
+    RequirementsResolvingSymbolRunner(symbol_runner, symbol_repo, PhantomData)
   }
 }
 
-impl<'s, R, G> SymbolRunner for RequirementsResolvingSymbolRunner<'s, R, G> where R: SymbolRunner, G: SymbolRepository<'s> {
+impl<'a, 's, R, G> SymbolRunner for RequirementsResolvingSymbolRunner<'a, 's, R, G> where R: SymbolRunner, G: SymbolRepository<'s> {
   fn run_symbol<S: ?Sized + Symbol + fmt::Display>(&self, logger: &mut Logger, symbol: &S) -> Result<(), Box<Error>>
   {
     for resource in symbol.get_prerequisites() {

src/symbols/dir.rs

@@ -2,7 +2,9 @@ use std::error::Error;
 use std::fmt;
 use std::fs;
 use std::io;
+use std::path::Path;
 
+use resources::Resource;
 use symbols::Symbol;
 
 pub struct Dir<D> where D: AsRef<str> + fmt::Display {
@@ -34,7 +36,19 @@ impl<D> Symbol for Dir<D> where D: AsRef<str> + fmt::Display {
   }
 
   fn execute(&self) -> Result<(), Box<Error>> {
-    fs::create_dir_all(self.path.as_ref()).map_err(|e| Box::new(e) as Box<Error>)
+    fs::create_dir(self.path.as_ref()).map_err(|e| Box::new(e) as Box<Error>)
+  }
+
+  fn get_prerequisites(&self) -> Vec<Resource> {
+    if let Some(parent) = Path::new(self.path.as_ref()).parent() {
+      vec![ Resource::new("dir", parent.to_string_lossy()) ]
+    } else {
+      vec![]
+    }
+  }
+
+  fn provides(&self) -> Option<Vec<Resource>> {
+    Some(vec![ Resource::new("dir", self.path.to_string()) ])
   }
 }
 

src/symbols/git/checkout.rs

@@ -1,8 +1,10 @@
 use std::error::Error;
 use std::fmt;
 use std::io;
+use std::path::Path;
 
 use command_runner::CommandRunner;
+use resources::Resource;
 use symbols::Symbol;
 
 pub struct GitCheckout<'a> {
@@ -67,6 +69,14 @@ impl<'a> Symbol for GitCheckout<'a> {
     try!(self._run_in_target_repo(&["merge", "FETCH_HEAD"]));
     Ok(())
   }
+
+  fn get_prerequisites(&self) -> Vec<Resource> {
+    vec![ Resource::new("dir", Path::new(self.target).parent().unwrap().to_string_lossy()) ]
+  }
+
+  fn provides(&self) -> Option<Vec<Resource>> {
+    Some(vec![ Resource::new("dir", self.target.to_string()) ])
+  }
 }
 
 #[cfg(test)]

src/symbols/hook.rs

@@ -31,6 +31,17 @@ impl<A, B> Symbol for Hook<A, B> where A: Symbol, B: Symbol {
     r.extend(self.b.get_prerequisites().into_iter());
     r
   }
+
+  fn provides(&self) -> Option<Vec<Resource>> {
+    let mut r = vec![];
+    if let Some(provides) = self.a.provides() {
+      r.extend(provides.into_iter());
+    }
+    if let Some(provides) = self.b.provides() {
+      r.extend(provides.into_iter());
+    }
+    if r.len() > 0 { Some(r) } else { None }
+  }
 }
 
 impl<A, B> fmt::Display for Hook<A, B> where A: Symbol, B: Symbol {

src/symbols/list.rs

@@ -32,6 +32,26 @@ impl<'a> Symbol for List<'a> {
     }
     Ok(())
   }
+
+  fn get_prerequisites(&self) -> Vec<Resource> {
+    let mut r = vec![];
+    for symbol in &self.symbols {
+      for req in symbol.get_prerequisites() {
+        if self.provides().map_or(true, |p| !p.contains(&req)) { r.push(req) }
+      }
+    }
+    r
+  }
+
+  fn provides(&self) -> Option<Vec<Resource>> {
+    let mut r = vec![];
+    for symbol in &self.symbols {
+      if let Some(provides) = symbol.provides() {
+        r.extend(provides.into_iter());
+      }
+    }
+    if r.len() > 0 { Some(r) } else { None }
+  }
 }
 
 impl<'a> fmt::Display for List<'a> {

src/symbols/mod.rs

@@ -8,6 +8,9 @@ pub trait Symbol: Display {
   fn get_prerequisites(&self) -> Vec<Resource> {
     vec![]
   }
+  fn provides(&self) -> Option<Vec<Resource>> {
+    None
+  }
 }
 
 pub mod acme;

src/symbols/user.rs

@@ -4,6 +4,7 @@ use std::fmt;
 use std::io::Error as IoError;
 
 use command_runner::CommandRunner;
+use resources::Resource;
 use symbols::Symbol;
 
 #[derive(Debug, PartialEq)]
@@ -108,6 +109,10 @@ impl<'a, E: 'static + Error, A: UserAdder<SubE=E>> Symbol for User<'a, E, A> {
   fn execute(&self) -> Result<(), Box<Error>> {
     self.user_adder.add_user(&*self.user_name).map_err(|e| Box::new(e) as Box<Error>)
   }
+
+  fn provides(&self) -> Option<Vec<Resource>> {
+    Some(vec![Resource::new("user", self.user_name.to_string())])
+  }
 }
 
 pub struct SystemUserAdder<'a> {