Simplify implementation using toml-query Partial

This patch rewrites the get_tags() function to use toml_query::read::Partial.

The helper functions is_tag_str and is_tag are rewritten for
compatiblity.

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>

lib/entry/libimagentrytag/Cargo.toml

@@ -26,12 +26,18 @@ toml = "0.5"
 itertools = "0.7"
 is-match = "0.1"
 filters = "0.3"
-toml-query = "0.9"
 failure    = "0.1"
+serde        = "1"
+serde_derive = "1"
 
 libimagstore = { version = "0.10.0", path = "../../../lib/core/libimagstore" }
 libimagerror = { version = "0.10.0", path = "../../../lib/core/libimagerror" }
 
+[dependencies.toml-query]
+version = "0.9"
+default-features = false
+features = [ "typed" ]
+
 [dependencies.clap]
 version = "^2.29"
 default-features = false

lib/entry/libimagentrytag/src/lib.rs

@@ -43,6 +43,8 @@ extern crate itertools;
 extern crate regex;
 extern crate toml;
 extern crate toml_query;
+extern crate serde;
+#[macro_use] extern crate serde_derive;
 #[macro_use] extern crate is_match;
 extern crate filters;
 #[macro_use] extern crate failure;

lib/entry/libimagentrytag/src/tag.rs

@@ -20,16 +20,17 @@
 use std::result::Result;
 
 use regex::Regex;
+use failure::Error;
 
 pub type Tag = String;
 pub type TagSlice<'a> = &'a str;
 
 /// validator which can be used by clap to validate that a string is a valid tag
 pub fn is_tag(s: String) -> Result<(), String> {
-    is_tag_str(&s)
+    is_tag_str(&s).map_err(|_| format!("The string '{}' is not a valid tag", s))
 }
 
-pub fn is_tag_str(s: &String) -> Result<(), String> {
+pub fn is_tag_str(s: &String) -> Result<(), Error> {
     use filters::filter::Filter;
     trace!("Checking whether '{}' is a valid tag", s);
 
@@ -41,7 +42,7 @@ pub fn is_tag_str(s: &String) -> Result<(), String> {
     if is_lower.and(no_whitespace).and(is_alphanum).and(matches_regex).filter(s) {
         Ok(())
     } else {
-        Err(format!("The string '{}' is not a valid tag", s))
+        Err(format_err!("The string '{}' is not a valid tag", s))
     }
 }
 

lib/entry/libimagentrytag/src/tagable.rs

@@ -23,6 +23,7 @@ use libimagstore::store::Entry;
 use libimagerror::errors::ErrorMsg as EM;
 
 use toml_query::read::TomlValueReadExt;
+use toml_query::read::Partial;
 use toml_query::insert::TomlValueInsertExt;
 
 use failure::Error;
@@ -47,42 +48,29 @@ pub trait Tagable {
 
 }
 
+#[derive(Serialize, Deserialize, Debug)]
+struct TagHeader {
+    values: Vec<String>,
+}
+
+impl<'a> Partial<'a> for TagHeader {
+    const LOCATION: &'static str = "tags";
+    type Output                  = Self;
+}
+
 impl Tagable for Value {
 
     fn get_tags(&self) -> Result<Vec<Tag>> {
-        self.read("tag.values")
-            .context(format_err!("Failed to read header at 'tag.values'"))
-            .map_err(Error::from)
-            .context(EM::EntryHeaderReadError)?
-            .map(|val| {
-                debug!("Got Value of tags...");
-                val.as_array()
-                    .map(|tags| {
-                        debug!("Got Array<T> of tags...");
-                        if !tags.iter().all(|t| is_match!(*t, Value::String(_))) {
-                            return Err(format_err!("Tag type error: Got Array<T> where T is not a String: {:?}", tags));
-                        }
-                        debug!("Got Array<String> of tags...");
-                        if tags.iter().any(|t| match *t {
-                            Value::String(ref s) => !is_tag_str(s).is_ok(),
-                            _ => unreachable!()})
-                        {
-                            return Err(format_err!("At least one tag is not a valid tag string"));
-                        }
+        self.read_partial::<TagHeader>()?
+            .map(|header| {
+                let _ = header.values
+                    .iter()
+                    .map(is_tag_str)
+                    .collect::<Result<_>>()?;
 
-                        Ok(tags.iter()
-                            .cloned()
-                            .map(|t| {
-                                match t {
-                                   Value::String(s) => s,
-                                   _ => unreachable!(),
-                                }
+                Ok(header.values)
             })
-                            .collect())
-                    })
-                    .unwrap_or(Ok(vec![]))
-            })
-            .unwrap_or(Ok(vec![]))
+            .unwrap_or_else(|| Ok(vec![]))
     }
 
     fn set_tags(&mut self, ts: &[Tag]) -> Result<()> {