Passing extra formatting options to LSPs (#2635)

* allows passing extra formatting options to LSPs

- adds optional field 'format' to [[language]] sections in 'languages.toml'

- passes specified options the LSPs via FormattingOptions

* cleaner conversion of formatting properties

* move formatting options inside lsp::Client

* cleans up formatting properties merge

4 files changed, 34 insertions, 0 deletions

diff --git a/book/src/languages.md b/book/src/languages.md
index 1fa24787..8c27785e 100644
--- a/book/src/languages.md
+++ b/book/src/languages.md
@@ -14,6 +14,18 @@ name = "rust"
 auto-format = false
 ```
 
+## LSP formatting options
+
+Use `format` field to pass extra formatting options to [Document Formatting Requests](https://github.com/microsoft/language-server-protocol/blob/gh-pages/_specifications/specification-3-16.md#document-formatting-request--leftwards_arrow_with_hook).
+
+```toml
+[[language]]
+name = "typescript"
+auto-format = true
+# pass format options according to https://github.com/typescript-language-server/typescript-language-server#workspacedidchangeconfiguration omitting the "[language].format." prefix.
+config = { format = { "semicolons" = "insert", "insertSpaceBeforeFunctionParenthesis" = true } }
+```
+
 ## Tree-sitter grammars
 
 Tree-sitter grammars can also be configured in `languages.toml`:
diff --git a/helix-core/src/syntax.rs b/helix-core/src/syntax.rs
index 1cfa04e7..ca497b64 100644
--- a/helix-core/src/syntax.rs
+++ b/helix-core/src/syntax.rs
@@ -78,6 +78,7 @@ pub struct LanguageConfiguration {
 
     #[serde(default)]
     pub auto_format: bool,
+
     #[serde(default)]
     pub diagnostic_severity: Severity,
 
diff --git a/helix-lsp/src/client.rs b/helix-lsp/src/client.rs
index 08201b3f..7f556ca6 100644
--- a/helix-lsp/src/client.rs
+++ b/helix-lsp/src/client.rs
@@ -7,7 +7,9 @@ use anyhow::anyhow;
 use helix_core::{find_root, ChangeSet, Rope};
 use jsonrpc_core as jsonrpc;
 use lsp_types as lsp;
+use serde::Deserialize;
 use serde_json::Value;
+use std::collections::HashMap;
 use std::future::Future;
 use std::process::Stdio;
 use std::sync::{
@@ -693,6 +695,24 @@ impl Client {
         };
         // TODO: return err::unavailable so we can fall back to tree sitter formatting
 
+        // merge FormattingOptions with 'config.format'
+        let config_format = self
+            .config
+            .as_ref()
+            .and_then(|cfg| cfg.get("format"))
+            .and_then(|fmt| HashMap::<String, lsp::FormattingProperty>::deserialize(fmt).ok());
+
+        let options = if let Some(mut properties) = config_format {
+            // passed in options take precedence over 'config.format'
+            properties.extend(options.properties);
+            lsp::FormattingOptions {
+                properties,
+                ..options
+            }
+        } else {
+            options
+        };
+
         let params = lsp::DocumentFormattingParams {
             text_document,
             options,
diff --git a/helix-view/src/document.rs b/helix-view/src/document.rs
index 9c3853c8..2c4b5de9 100644
--- a/helix-view/src/document.rs
+++ b/helix-view/src/document.rs
@@ -410,6 +410,7 @@ impl Document {
         let language_server = self.language_server()?;
         let text = self.text.clone();
         let offset_encoding = language_server.offset_encoding();
+
         let request = language_server.text_document_formatting(
             self.identifier(),
             lsp::FormattingOptions {