Merge #6140

6140: honour hover.content_format client capability r=lnicola a=robinvd

This removes all markdown when the client does not support the markdown MarkupKind.

Otherwise the output on the editor will have some markdown boilerplate, making it less readable.

For example kak_lsp does not currently support markdown.
![image](https://user-images.githubusercontent.com/22073483/95112949-ef0ff080-0741-11eb-82a7-0594fa2cd736.png)

after:
![image](https://user-images.githubusercontent.com/22073483/95113089-2bdbe780-0742-11eb-94fa-bcfec6d7347a.png)



Co-authored-by: Robin van Dijk <robin@robinjint.nl>

crates/rust-analyzer/src/config.rs

@@ -15,7 +15,7 @@ use ide::{
     AssistConfig, CompletionConfig, DiagnosticsConfig, HoverConfig, InlayHintsConfig,
     MergeBehaviour,
 };
-use lsp_types::ClientCapabilities;
+use lsp_types::{ClientCapabilities, MarkupKind};
 use project_model::{CargoConfig, ProjectJson, ProjectJsonData, ProjectManifest};
 use rustc_hash::FxHashSet;
 use serde::Deserialize;
@@ -333,6 +333,7 @@ impl Config {
             debug: data.hoverActions_enable && data.hoverActions_debug,
             goto_type_def: data.hoverActions_enable && data.hoverActions_gotoTypeDef,
             links_in_hover: data.hoverActions_linksInHover,
+            markdown: true,
         };
 
         log::info!("Config::update() = {:#?}", self);
@@ -340,6 +341,9 @@ impl Config {
 
     pub fn update_caps(&mut self, caps: &ClientCapabilities) {
         if let Some(doc_caps) = caps.text_document.as_ref() {
+            if let Some(value) = doc_caps.hover.as_ref().and_then(|it| it.content_format.as_ref()) {
+                self.hover.markdown = value.contains(&MarkupKind::Markdown)
+            }
             if let Some(value) = doc_caps.definition.as_ref().and_then(|it| it.link_support) {
                 self.client_caps.location_link = value;
             }