feat(lsp): add handlers for inlay hints (#23736)

initial support; public API left for a follow-up PR

2 files changed, 135 insertions, 1 deletions

diff --git a/test/functional/plugin/lsp/inlay_hint_spec.lua b/test/functional/plugin/lsp/inlay_hint_spec.lua
new file mode 100644
index 0000000000..b134095c4f
--- /dev/null
+++ b/test/functional/plugin/lsp/inlay_hint_spec.lua
@@ -0,0 +1,132 @@
+local helpers = require('test.functional.helpers')(after_each)
+local lsp_helpers = require('test.functional.plugin.lsp.helpers')
+local Screen = require('test.functional.ui.screen')
+
+local dedent = helpers.dedent
+local exec_lua = helpers.exec_lua
+local insert = helpers.insert
+
+local clear_notrace = lsp_helpers.clear_notrace
+local create_server_definition = lsp_helpers.create_server_definition
+
+before_each(function()
+  clear_notrace()
+end)
+
+after_each(function()
+  exec_lua("vim.api.nvim_exec_autocmds('VimLeavePre', { modeline = false })")
+end)
+
+describe('inlay hints', function()
+  local screen
+  before_each(function()
+    screen = Screen.new(50, 9)
+    screen:attach()
+  end)
+
+  describe('general', function()
+    local text = dedent([[
+    auto add(int a, int b) { return a + b; }
+
+    int main() {
+        int x = 1;
+        int y = 2;
+        return add(x,y);
+    }
+    }]])
+
+
+    local response = [==[
+    [
+    {"kind":1,"paddingLeft":false,"label":"-> int","position":{"character":22,"line":0},"paddingRight":false},
+    {"kind":2,"paddingLeft":false,"label":"a:","position":{"character":15,"line":5},"paddingRight":true},
+    {"kind":2,"paddingLeft":false,"label":"b:","position":{"character":17,"line":5},"paddingRight":true}
+    ]
+    ]==]
+
+
+    before_each(function()
+      exec_lua(create_server_definition)
+      exec_lua([[
+        local response = ...
+        server = _create_server({
+          capabilities = {
+            inlayHintProvider = true,
+          },
+          handlers = {
+            ['textDocument/inlayHint'] = function()
+              return vim.json.decode(response)
+            end,
+          }
+        })
+      ]], response)
+    end)
+
+    it(
+      'inlay hints are applied when vim.lsp._inlay_hint.refresh() is called',
+      function()
+        exec_lua([[
+        bufnr = vim.api.nvim_get_current_buf()
+        vim.api.nvim_win_set_buf(0, bufnr)
+        client_id = vim.lsp.start({ name = 'dummy', cmd = server.cmd })
+      ]])
+
+        insert(text)
+        exec_lua([[vim.lsp._inlay_hint.refresh({bufnr = bufnr})]])
+        screen:expect({
+          grid = [[
+  auto add(int a, int b)-> int { return a + b; }    |
+                                                    |
+  int main() {                                      |
+      int x = 1;                                    |
+      int y = 2;                                    |
+      return add(a: x,b: y);                        |
+  }                                                 |
+  ^}                                                 |
+                                                    |
+]]
+        })
+      end)
+
+    it(
+      'inlay hints are cleared when vim.lsp._inlay_hint.clear() is called',
+      function()
+        exec_lua([[
+        bufnr = vim.api.nvim_get_current_buf()
+        vim.api.nvim_win_set_buf(0, bufnr)
+        client_id = vim.lsp.start({ name = 'dummy', cmd = server.cmd })
+      ]])
+
+        insert(text)
+        exec_lua([[vim.lsp._inlay_hint.refresh({bufnr = bufnr})]])
+        screen:expect({
+          grid = [[
+  auto add(int a, int b)-> int { return a + b; }    |
+                                                    |
+  int main() {                                      |
+      int x = 1;                                    |
+      int y = 2;                                    |
+      return add(a: x,b: y);                        |
+  }                                                 |
+  ^}                                                 |
+                                                    |
+]]
+        })
+        exec_lua([[vim.lsp._inlay_hint.clear()]])
+        screen:expect({
+          grid = [[
+  auto add(int a, int b) { return a + b; }          |
+                                                    |
+  int main() {                                      |
+      int x = 1;                                    |
+      int y = 2;                                    |
+      return add(x,y);                              |
+  }                                                 |
+  ^}                                                 |
+                                                    |
+]],
+          unchanged = true
+        })
+      end)
+  end)
+end)
diff --git a/test/functional/plugin/lsp_spec.lua b/test/functional/plugin/lsp_spec.lua
index 85138417ff..2f4a703c74 100644
--- a/test/functional/plugin/lsp_spec.lua
+++ b/test/functional/plugin/lsp_spec.lua
@@ -3230,9 +3230,10 @@ describe('LSP', function()
           eq(0, signal, "exit signal")
         end;
         on_handler = function(err, result, ctx)
-          -- Don't compare & assert params, they're not relevant for the testcase
+          -- Don't compare & assert params and version, they're not relevant for the testcase
           -- This allows us to be lazy and avoid declaring them
           ctx.params = nil
+          ctx.version = nil
 
           eq(table.remove(test.expected_handlers), {err, result, ctx}, "expected handler")
           if ctx.method == 'start' then
@@ -3314,6 +3315,7 @@ describe('LSP', function()
         end,
         on_handler = function(err, result, ctx)
           ctx.params = nil -- don't compare in assert
+          ctx.version = nil
           eq(table.remove(expected_handlers), { err, result, ctx })
           if ctx.method == 'start' then
             exec_lua([[