examples: add minimal_lsp.rs and FIFO test script (#20017)

* `examples/minimal_lsp.rs` – compact LSP server showing definition,
  completion, hover, rustfmt-based formatting, and dummy diagnostics.
  Advertises UTF-8 offset encoding.

* `examples/manual_test.sh` – FIFO script that streams the canonical
  nine LSP packets so anyone can validate the server from two terminals.

No new runtime deps; `anyhow` stays under [dev-dependencies].

Author: shashi1687

lib/lsp-server/Cargo.toml

@@ -16,6 +16,7 @@ crossbeam-channel.workspace = true
 [dev-dependencies]
 lsp-types = "=0.95"
 ctrlc = "3.4.7"
+anyhow = "1.0.98"
 
 [lints]
 workspace = true

lib/lsp-server/examples/goto_def.rs

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+# Simple nine-packet LSP test for examples/minimal_lsp.rs
+# Usage: bash examples/manual_test.sh            # defaults to /tmp/lsp_pipe
+#        bash examples/manual_test.sh mypipe     # custom fifo name
+
+set -eu
+PIPE=${1:-/tmp/lsp_pipe}
+
+mkfifo -m 600 "$PIPE" 2>/dev/null || true       # create once, ignore if exists
+
+# open write end so the fifo stays open
+exec 3> "$PIPE"
+
+send() {
+  local body=$1
+  local len=$(printf '%s' "$body" | wc -c)
+  printf 'Content-Length: %d\r\n\r\n%s' "$len" "$body" >&3
+}
+
+send '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"capabilities":{}}}'
+send '{"jsonrpc":"2.0","method":"initialized","params":{}}'
+send '{"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{"uri":"file:///tmp/foo.rs","languageId":"rust","version":1,"text":"fn  main( ){println!(\"hi\") }"}}}'
+send '{"jsonrpc":"2.0","id":2,"method":"textDocument/completion","params":{"textDocument":{"uri":"file:///tmp/foo.rs"},"position":{"line":0,"character":0}}}'
+send '{"jsonrpc":"2.0","id":3,"method":"textDocument/hover","params":{"textDocument":{"uri":"file:///tmp/foo.rs"},"position":{"line":0,"character":0}}}'
+send '{"jsonrpc":"2.0","id":4,"method":"textDocument/definition","params":{"textDocument":{"uri":"file:///tmp/foo.rs"},"position":{"line":0,"character":0}}}'
+send '{"jsonrpc":"2.0","id":5,"method":"textDocument/formatting","params":{"textDocument":{"uri":"file:///tmp/foo.rs"},"options":{"tabSize":4,"insertSpaces":true}}}'
+send '{"jsonrpc":"2.0","id":6,"method":"shutdown","params":null}'
+send '{"jsonrpc":"2.0","method":"exit","params":null}'
+
+exec 3>&-
+echo "Packets sent – watch the other terminal for responses."