Add --update-only flag to cargo-add

This adds the specified dependency/ies only if they are already present. Thus, it acts like a 'cargo upgrade' (see killercup#74)

src/bin/add/args.rs

@@ -43,6 +43,8 @@ pub struct Args {
     pub flag_version: bool,
     /// `---upgrade`
     pub flag_upgrade: Option<String>,
+    /// `--update-only`
+    pub flag_update_only: bool,
     /// '--fetch-prereleases'
     pub flag_allow_prerelease: bool,
 }
@@ -144,6 +146,7 @@ impl Default for Args {
             flag_manifest_path: None,
             flag_version: false,
             flag_upgrade: None,
+            flag_update_only: false,
             flag_allow_prerelease: false,
         }
     }

src/bin/add/main.rs

@@ -52,6 +52,7 @@ Options:
     --upgrade=<method>      Choose method of semantic version upgrade. Must be one of
                             "none" (exact version), "patch" (`~` modifier), "minor"
                             (`^` modifier, default), or "all" (`>=`).
+    --update-only           Only add the updated dependency if it already exists.
     --manifest-path=<path>  Path to the manifest to add a dependency to.
     --allow-prerelease      Include prerelease versions when fetching from crates.io (e.g.
                             '0.6.0-alpha'). Defaults to false.
@@ -72,12 +73,17 @@ fn handle_add(args: &Args) -> Result<(), Box<Error>> {
     let mut manifest = try!(Manifest::open(&args.flag_manifest_path.as_ref().map(|s| &s[..])));
     let deps = try!(args.parse_dependencies());
 
-    for dep in deps {
-        if let Err(err) = manifest.insert_into_table(&args.get_section(), &dep) {
+    deps
+        .iter()
+        .map(|dep| if args.flag_update_only {
+            manifest.update_table_entry(&args.get_section(), &dep)
+        } else {
+            manifest.insert_into_table(&args.get_section(), &dep)})
+        .collect::<Result<Vec<_>,_>>()
+        .map_err(|err| {
             println!("Could not edit `Cargo.toml`.\n\nERROR: {}", err);
-            return Err(From::from(err));
-        }
-    }
+            err
+        })?;
 
     let mut file = try!(Manifest::find_file(&args.flag_manifest_path.as_ref().map(|s| &s[..])));
     manifest.write_to_file(&mut file)

src/manifest.rs

@@ -165,9 +165,8 @@ impl Manifest {
                              dep: &Dependency)
                              -> Result<(), ManifestError> {
         let (ref name, ref data) = dep.to_toml();
-        let manifest = &mut self.data;
 
-        let mut entry = manifest;
+        let mut entry = &mut self.data;
         for part in table {
             let tmp_entry = entry; // Make the borrow checker happy
             let value = tmp_entry.entry(part.clone())
@@ -181,6 +180,30 @@ impl Manifest {
         Ok(())
     }
 
+    /// Update an entry in Cargo.toml.
+    #[cfg_attr(feature = "dev", allow(toplevel_ref_arg))]
+    pub fn update_table_entry(&mut self,
+                              table: &[String],
+                              dep: &Dependency)
+                              -> Result<(), ManifestError> {
+        let (ref name, ref data) = dep.to_toml();
+
+        let mut entry = &mut self.data;
+        for part in table {
+            let tmp_entry = entry; // Make the borrow checker happy
+            let value = tmp_entry.entry(part.clone())
+                .or_insert_with(|| toml::Value::Table(BTreeMap::new()));
+            match *value {
+                toml::Value::Table(ref mut table) => entry = table,
+                _ => return Err(ManifestError::NonExistentTable(part.clone())),
+            }
+        }
+        if entry.contains_key(name) {
+            entry.insert(name.clone(), data.clone());
+        }
+        Ok(())
+    }
+
     /// Remove entry from a Cargo.toml.
     ///
     /// # Examples
@@ -277,6 +300,29 @@ mod tests {
         assert_eq!(manifest, clone);
     }
 
+    #[test]
+    fn update_dependency() {
+        let mut manifest = Manifest { data: toml::Table::new() };
+        let dep = Dependency::new("cargo-edit").set_version("0.1.0");
+        manifest.insert_into_table(&["dependencies".to_owned()], &dep).unwrap();
+
+        let new_dep = Dependency::new("cargo-edit").set_version("0.2.0");
+        manifest.update_table_entry(&["dependencies".to_owned()], &new_dep).unwrap();
+    }
+
+    #[test]
+    fn update_wrong_dependency() {
+        let mut manifest = Manifest { data: toml::Table::new() };
+        let dep = Dependency::new("cargo-edit").set_version("0.1.0");
+        manifest.insert_into_table(&["dependencies".to_owned()], &dep).unwrap();
+        let original = manifest.clone();
+
+        let new_dep = Dependency::new("wrong-dep").set_version("0.2.0");
+        manifest.update_table_entry(&["dependencies".to_owned()], &new_dep).unwrap();
+
+        assert_eq!(manifest, original);
+    }
+
     #[test]
     fn remove_dependency_no_section() {
         let mut manifest = Manifest { data: toml::Table::new() };