Merge #6519

6519: Add "Open Cargo.toml" action r=matklad a=p3achyjr

## What is it?

This adds an "open cargo.toml" action from the vscode shell, resolves #6462 

## Test

Ran ```cargo xtask install --server``` and ```cargo xtask install --client```, then ```Developer: Reload Window```.

![image](https://user-images.githubusercontent.com/8763808/98614382-2a578f00-22ad-11eb-9811-4a72a54ff6fb.png)

When clicked:

![image](https://user-images.githubusercontent.com/8763808/98618176-77d7fa00-22b5-11eb-8788-35256542f3a6.png)


Co-authored-by: Anatol Liu <[email protected]>

1 files changed, 27 insertions, 2 deletions

diff --git a/docs/dev/lsp-extensions.md b/docs/dev/lsp-extensions.md
index 77d4e0ec9..db9727bee 100644
--- a/docs/dev/lsp-extensions.md
+++ b/docs/dev/lsp-extensions.md
@@ -1,8 +1,8 @@
 <!---
-lsp_ext.rs hash: 4f86fb54e4b2870e
+lsp_ext.rs hash: 9d5daed5b25dc4f6
 
 If you need to change the above hash to make the test pass, please check if you
-need to adjust this doc as well and ping this issue:
+need to adjust this doc as well and ping this  issue:
 
   https://github.com/rust-analyzer/rust-analyzer/issues/4604
 
@@ -537,3 +537,28 @@ Such actions on the client side are appended to a hover bottom as command links:
   +-----------------------------+
   ...
 ```
+
+## Open Cargo.toml
+
+**Issue:** https://github.com/rust-analyzer/rust-analyzer/issues/6462
+
+This request is sent from client to server to open the current project's Cargo.toml
+
+**Method:** `experimental/openCargoToml`
+
+**Request:** `OpenCargoTomlParams`
+
+**Response:** `Location | null`
+
+
+### Example
+
+```rust
+// Cargo.toml
+[package]
+// src/main.rs
+
+/* cursor here*/
+```
+
+`experimental/openCargoToml` returns a single `Link` to the start of the `[package]` keyword.