language server over stdio, emacs mode with repl and eglot wiring

3 files changed, 171 insertions, 2 deletions

diff --git a/bin/dune b/bin/dune
index 1ad9289..049ef66 100644
--- a/bin/dune
+++ b/bin/dune
@@ -1,4 +1,5 @@
 (executable
  (name main)
  (public_name sol)
- (libraries sol))
+ (modules main lsp)
+ (libraries sol yojson))
diff --git a/bin/lsp.ml b/bin/lsp.ml
new file mode 100644
index 0000000..bfe2573
--- /dev/null
+++ b/bin/lsp.ml
@@ -0,0 +1,166 @@
+(* The Sol language server: JSON-RPC over stdio, hand rolled on
+   yojson. One capability, the load-bearing one: diagnostics. Every
+   edit runs the same admission the runtime runs, so a rule with no
+   decrease witness or a fact violating its schema is an error in
+   the editor, at typing time, with the same message the loader
+   gives. Parse errors carry positions; admission errors anchor at
+   the top of the file until the loader learns locations. *)
+
+let log_json json = Yojson.Safe.to_string json
+
+let send json =
+  let body = log_json json in
+  Printf.printf "Content-Length: %d\r\n\r\n%s" (String.length body) body;
+  flush stdout
+
+let read_message () =
+  let rec headers length =
+    match In_channel.input_line stdin with
+    | None -> None
+    | Some line -> (
+        let line = String.trim line in
+        if line = "" then length
+        else
+          match String.index_opt line ':' with
+          | Some i
+            when String.lowercase_ascii (String.sub line 0 i) = "content-length"
+            ->
+              headers
+                (int_of_string_opt
+                   (String.trim
+                      (String.sub line (i + 1) (String.length line - i - 1))))
+          | _ -> headers length)
+  in
+  match headers None with
+  | None -> None
+  | Some length -> (
+      match really_input_string stdin length with
+      | body -> ( try Some (Yojson.Safe.from_string body) with _ -> None)
+      | exception End_of_file -> None)
+
+let member name json =
+  match json with
+  | `Assoc fields -> Option.value ~default:`Null (List.assoc_opt name fields)
+  | _ -> `Null
+
+let to_string_opt = function `String s -> Some s | _ -> None
+
+(* Everything the checker can say about a document, as LSP
+   diagnostics: (line, column, message), zero-based lines. *)
+let diagnostics text =
+  match Sol.Front.parse text with
+  | Error { Sol.Front.line; column; message } ->
+      [ (max 0 (line - 1), max 0 column, message) ]
+  | Ok statements -> (
+      match Sol.Program.load statements with
+      | Error error -> [ (0, 0, Format.asprintf "%a" Sol.Program.pp_error error) ]
+      | Ok _ -> [])
+
+let publish uri text =
+  let items =
+    List.map
+      (fun (line, column, message) ->
+        `Assoc
+          [
+            ( "range",
+              `Assoc
+                [
+                  ( "start",
+                    `Assoc [ ("line", `Int line); ("character", `Int column) ]
+                  );
+                  ( "end",
+                    `Assoc
+                      [ ("line", `Int line); ("character", `Int (column + 1)) ]
+                  );
+                ] );
+            ("severity", `Int 1);
+            ("source", `String "sol");
+            ("message", `String message);
+          ])
+      (diagnostics text)
+  in
+  send
+    (`Assoc
+      [
+        ("jsonrpc", `String "2.0");
+        ("method", `String "textDocument/publishDiagnostics");
+        ("params", `Assoc [ ("uri", `String uri); ("diagnostics", `List items) ]);
+      ])
+
+let respond id result =
+  send (`Assoc [ ("jsonrpc", `String "2.0"); ("id", id); ("result", result) ])
+
+let check_notification params =
+  let uri =
+    to_string_opt (member "uri" (member "textDocument" params))
+  in
+  let text =
+    match to_string_opt (member "text" (member "textDocument" params)) with
+    | Some text -> Some text
+    | None -> (
+        (* didChange, full sync: the last full content change. *)
+        match member "contentChanges" params with
+        | `List changes -> (
+            match List.rev changes with
+            | last :: _ -> to_string_opt (member "text" last)
+            | [] -> None)
+        | _ -> None)
+  in
+  match (uri, text) with Some uri, Some text -> publish uri text | _ -> ()
+
+let run () =
+  set_binary_mode_in stdin true;
+  set_binary_mode_out stdout true;
+  let running = ref true in
+  while !running do
+    match read_message () with
+    | None -> running := false
+    | Some message -> (
+        let id = member "id" message in
+        let params = member "params" message in
+        match to_string_opt (member "method" message) with
+        | Some "initialize" ->
+            respond id
+              (`Assoc
+                [
+                  ( "capabilities",
+                    `Assoc [ ("textDocumentSync", `Int 1) ] );
+                  ( "serverInfo",
+                    `Assoc
+                      [
+                        ("name", `String "sol-lsp"); ("version", `String "0.1.0");
+                      ] );
+                ])
+        | Some "shutdown" -> respond id `Null
+        | Some "exit" -> running := false
+        | Some ("textDocument/didOpen" | "textDocument/didChange") ->
+            check_notification params
+        | Some "textDocument/didClose" -> (
+            match to_string_opt (member "uri" (member "textDocument" params)) with
+            | Some uri ->
+                send
+                  (`Assoc
+                    [
+                      ("jsonrpc", `String "2.0");
+                      ("method", `String "textDocument/publishDiagnostics");
+                      ( "params",
+                        `Assoc
+                          [ ("uri", `String uri); ("diagnostics", `List []) ] );
+                    ])
+            | None -> ())
+        | Some _ when id <> `Null ->
+            (* An unsupported request deserves an answer, not silence. *)
+            send
+              (`Assoc
+                [
+                  ("jsonrpc", `String "2.0");
+                  ("id", id);
+                  ( "error",
+                    `Assoc
+                      [
+                        ("code", `Int (-32601));
+                        ("message", `String "method not found");
+                      ] );
+                ])
+        | _ -> ())
+  done
diff --git a/bin/main.ml b/bin/main.ml
index c5c329a..eb212d2 100644
--- a/bin/main.ml
+++ b/bin/main.ml
@@ -48,6 +48,7 @@ let repl () =
   print_endline "Sol. Statements accumulate; Query expression: ... runs.";
   let rec loop history =
     print_string "sol> ";
+    flush stdout;
     match In_channel.input_line stdin with
     | None -> ()
     | Some line when String.trim line = "" -> loop history
@@ -73,7 +74,8 @@ let repl () =
 let () =
   match Sys.argv with
   | [| _ |] -> repl ()
+  | [| _; "lsp" |] -> Lsp.run ()
   | [| _; path |] -> run_file path
   | _ ->
-      prerr_endline "usage: sol [file.sol]";
+      prerr_endline "usage: sol [file.sol | lsp]";
       exit 1