Merge #7657

7657: utf8 r=matklad a=matklad

- Prepare for utf-8 offsets
- reduce code duplication in tests
- Make utf8 default, implement utf16 in terms of it
- Make it easy to add additional context for offset conversion
- Implement utf8 offsets

closes #7453

Co-authored-by: Aleksey Kladov <aleksey.kladov@gmail.com>

crates/rust-analyzer/src/config.rs

@@ -23,7 +23,10 @@ use rustc_hash::FxHashSet;
 use serde::{de::DeserializeOwned, Deserialize};
 use vfs::AbsPathBuf;
 
-use crate::{caps::completion_item_edit_resolve, diagnostics::DiagnosticsMapConfig};
+use crate::{
+    caps::completion_item_edit_resolve, diagnostics::DiagnosticsMapConfig,
+    line_index::OffsetEncoding, lsp_ext::supports_utf8,
+};
 
 config_data! {
     struct ConfigData {
@@ -415,6 +418,13 @@ impl Config {
             false
         )
     }
+    pub fn offset_encoding(&self) -> OffsetEncoding {
+        if supports_utf8(&self.caps) {
+            OffsetEncoding::Utf8
+        } else {
+            OffsetEncoding::Utf16
+        }
+    }
 
     fn experimental(&self, index: &'static str) -> bool {
         try_or!(self.caps.experimental.as_ref()?.get(index)?.as_bool()?, false)