Refactor decoding errors with more improvements

[chshersh]

Custom decoding errors were implemented in the following PR:

• Provide more detailed TOML decoding errors #122

This issue is about some minor improvements to the implementation so they can be done separately:

• Move Value::String("some value") into const EXPECTED_STRING or STRING_TYPE. It's a hack to reuse toml::Value for types of expected values. We can move them into top-level constants for easier reuse in the future:

• tool-sync/src/config/toml.rs

  Line 106 in f345444

  expected: Value::String("some_value".into()),

• Return error when asset_name is not a table. Currently we return empty AssetName but we should provide a custom error when it's something like asset_name = "x86_64_unknown_linux_musl". Implement a similar constant to the previous task for string

• tool-sync/src/config/toml.rs

  Lines 163 to 168 in f345444

  	match table.get("asset_name").and_then(|t| t.as_table()) {
  	None => AssetName {
  	linux: None,
  	macos: None,
  	windows: None,
  	},

• Return error when str_by_key doesn't see String. The function returns Option<String>. Its type should be changed to Result<Option<String>, DecodeError> and its name should be changed to optional_str_by_key. And this function should throw an error when it sees something besides string.

• tool-sync/src/config/toml.rs

  Lines 184 to 186 in f345444

  	fn str_by_key(table: &Map<String, Value>, key: &str) -> Option<String> {
  	table.get(key).and_then(|v| v.as_str()).map(String::from)
  	}

• Throw DecodeError when iterating through the map. We expect all tools to be tables. So we should iterate through the map, filter out expected keys (proxy and store_directory) and throw an error otherwise

• tool-sync/src/config/toml.rs

  Lines 124 to 126 in f345444

  	if let Value::Table(table) = val {
  	tools.insert(key.clone(), decode_config_asset(table, &proxy));
  	}

[chshersh]

@DukeManh I created this issue as a follow-up to your improvements in #122. You don't need to implement this issue (unless you want to), someone else could contribute the improvements 🙂 You've created the mechanism but in this issue I propose to use it in even more places.

[ChellappanRajan]

Hi @chshersh I would like to work on this issue. Can you please assign it on my name?

[chshersh]

Hi @ChellappanRajan 👋🏻
Sure, go for it 👍🏻