feat: add signature help

Author: lucacervello

lib/next_ls.ex

@@ -24,6 +24,7 @@ defmodule NextLS do
   alias GenLSP.Requests.TextDocumentFormatting
   alias GenLSP.Requests.TextDocumentHover
   alias GenLSP.Requests.TextDocumentReferences
+  alias GenLSP.Requests.TextDocumentSignatureHelp
   alias GenLSP.Requests.WorkspaceApplyEdit
   alias GenLSP.Requests.WorkspaceSymbol
   alias GenLSP.Structures.ApplyWorkspaceEditParams
@@ -41,6 +42,8 @@ defmodule NextLS do
   alias GenLSP.Structures.Range
   alias GenLSP.Structures.SaveOptions
   alias GenLSP.Structures.ServerCapabilities
+  alias GenLSP.Structures.SignatureHelp
+  alias GenLSP.Structures.SignatureHelpParams
   alias GenLSP.Structures.SymbolInformation
   alias GenLSP.Structures.TextDocumentIdentifier
   alias GenLSP.Structures.TextDocumentItem
@@ -53,6 +56,7 @@ defmodule NextLS do
   alias NextLS.DiagnosticCache
   alias NextLS.Progress
   alias NextLS.Runtime
+  alias NextLS.SignatureHelp
 
   require NextLS.Runtime
 
@@ -157,6 +161,9 @@ defmodule NextLS do
              "alias-refactor"
            ]
          },
+         signature_help_provider: %GenLSP.Structures.SignatureHelpOptions{
+           trigger_characters: ["(", ","]
+         },
          hover_provider: true,
          workspace_symbol_provider: true,
          document_symbol_provider: true,
@@ -817,6 +824,34 @@ defmodule NextLS do
       {:reply, nil, lsp}
   end
 
+  def handle_request(
+        %TextDocumentSignatureHelp{params: %SignatureHelpParams{text_document: %{uri: uri}, position: position}},
+        lsp
+      ) do
+    signature_help =
+      case SignatureHelp.fetch_mod_and_name(uri, {position.line + 1, position.character + 1}) do
+        {:ok, {mod, name}} ->
+          docs =
+            dispatch(lsp.assigns.registry, :runtimes, fn entries ->
+              [result] =
+                for {runtime, %{uri: wuri}} <- entries, String.starts_with?(uri, wuri) do
+                  Runtime.call(runtime, {Code, :fetch_docs, [mod]})
+                end
+
+              result
+            end)
+
+          docs
+          |> SignatureHelp.format(name)
+          |> List.first()
+
+        {:error, :not_found} ->
+          nil
+      end
+
+    {:reply, signature_help, lsp}
+  end
+
   def handle_request(%Shutdown{}, lsp) do
     {:reply, nil, assign(lsp, exit_code: 0)}
   end

lib/next_ls/signature_help.ex

@@ -0,0 +1,94 @@
+defmodule NextLS.SignatureHelp do
+  @moduledoc false
+
+  alias GenLSP.Enumerations.MarkupKind
+  alias GenLSP.Structures.MarkupContent
+  alias GenLSP.Structures.ParameterInformation
+  alias GenLSP.Structures.SignatureHelp
+  alias GenLSP.Structures.SignatureInformation
+  alias Sourceror.Zipper
+
+  def fetch_mod_and_name(uri, position) do
+    with {:ok, text} <- File.read(URI.parse(uri).path),
+         ast =
+           text
+           |> Spitfire.parse()
+           |> then(fn
+             {:ok, ast} -> ast
+             {:error, ast, _} -> ast
+           end),
+         {:ok, result} <- find_node(ast, position) do
+      case result do
+        {{:., _, [{:__aliases__, _, modules}, name]}, _, _} -> {:ok, {Module.concat(modules), name}}
+      end
+    end
+  end
+
+  def format({:ok, {:docs_v1, _, :elixir, _, _, _, docs}}, func_name) do
+    docs
+    |> Enum.filter(fn
+      {{_, name, _arity}, _, _, _, _} -> name == func_name
+    end)
+    |> Enum.map(fn
+      {{_, _name, _arity}, _, [signature], _, _} ->
+        params_info =
+          signature
+          |> Spitfire.parse!()
+          |> then(fn {_, _, args} ->
+            Enum.map(args, fn {name, _, _} -> name end)
+          end)
+          |> Enum.map(fn name ->
+            %ParameterInformation{
+              label: Atom.to_string(name)
+            }
+          end)
+
+        %SignatureHelp{
+          signatures: [
+            %SignatureInformation{
+              label: signature,
+              parameters: params_info,
+              documentation: %MarkupContent{
+                kind: MarkupKind.markdown(),
+                value: ""
+              }
+            }
+          ]
+        }
+
+      # {{_, _name, _arity}, _, [], _, _} ->
+      #   []
+
+      _otherwise ->
+        []
+    end)
+  end
+
+  def format({:ok, {:error, :module_not_found}}, _func_name) do
+    []
+  end
+
+  defp find_node(ast, {line, column}) do
+    position = [line: line, column: column]
+
+    result =
+      ast
+      |> Zipper.zip()
+      |> Zipper.find(fn
+        {{:., _, _}, _metadata, _} = node ->
+          range = Sourceror.get_range(node)
+
+          Sourceror.compare_positions(range.start, position) == :lt &&
+            Sourceror.compare_positions(range.end, position) == :gt
+
+        _ ->
+          false
+      end)
+
+    if result do
+      {:ok, Zipper.node(result)}
+    else
+      {:error, :not_found}
+    end
+  end
+end