feat(lsp): highlight semantic token modifiers (#21390)

Apply semantic token modifiers as separate extmarks with corresponding
highlight groups (e.g., `@readonly`). This is a low-effort PR to enable
the most common use cases (applying, e.g., italics or backgrounds on top
of type highlights; language-specific fallbacks like `@global.lua` are
also available). This can be replaced by more complicated selector-style
themes later on.

3 files changed, 30 insertions, 17 deletions

diff --git a/runtime/doc/lsp.txt b/runtime/doc/lsp.txt
index 89a6e89511..75d5c067b1 100644
--- a/runtime/doc/lsp.txt
+++ b/runtime/doc/lsp.txt
@@ -1340,7 +1340,7 @@ start({bufnr}, {client_id}, {opts})          *vim.lsp.semantic_tokens.start()*
     |vim.lsp.buf_attach_client()|. To opt-out of semantic highlighting with a
     server that supports it, you can delete the semanticTokensProvider table
     from the {server_capabilities} of your client in your |LspAttach| callback
-    or your configuration's `on_attach` callback. >lua
+    or your configuration's `on_attach` callback: >lua
 
        client.server_capabilities.semanticTokensProvider = nil
 <
diff --git a/runtime/lua/vim/lsp/semantic_tokens.lua b/runtime/lua/vim/lsp/semantic_tokens.lua
index f06d136801..b7ffedab2b 100644
--- a/runtime/lua/vim/lsp/semantic_tokens.lua
+++ b/runtime/lua/vim/lsp/semantic_tokens.lua
@@ -409,7 +409,17 @@ function STHighlighter:on_win(topline, botline)
             strict = false,
           })
 
-          --TODO(jdrouhard): do something with the modifiers
+          -- TODO(bfredl) use single extmark when hl_group supports table
+          if #token.modifiers > 0 then
+            for _, modifier in pairs(token.modifiers) do
+              api.nvim_buf_set_extmark(self.bufnr, state.namespace, token.line, token.start_col, {
+                hl_group = '@' .. modifier,
+                end_col = token.end_col,
+                priority = vim.highlight.priorities.semantic_tokens,
+                strict = false,
+              })
+            end
+          end
 
           token.extmark_added = true
         end
@@ -494,7 +504,7 @@ local M = {}
 --- opt-out of semantic highlighting with a server that supports it, you can
 --- delete the semanticTokensProvider table from the {server_capabilities} of
 --- your client in your |LspAttach| callback or your configuration's
---- `on_attach` callback.
+--- `on_attach` callback:
 --- <pre>lua
 ---   client.server_capabilities.semanticTokensProvider = nil
 --- </pre>
diff --git a/test/functional/plugin/lsp/semantic_tokens_spec.lua b/test/functional/plugin/lsp/semantic_tokens_spec.lua
index e87e2a3334..e62a6f7086 100644
--- a/test/functional/plugin/lsp/semantic_tokens_spec.lua
+++ b/test/functional/plugin/lsp/semantic_tokens_spec.lua
@@ -69,9 +69,12 @@ describe('semantic token highlighting', function()
         [4] = { bold = true, foreground = Screen.colors.SeaGreen };
         [5] = { foreground = tonumber('0x6a0dad') };
         [6] = { foreground = Screen.colors.Blue1 };
+        [7] = { bold = true, foreground = Screen.colors.DarkCyan };
+        [8] = { bold = true, foreground = Screen.colors.SlateBlue };
       }
       command([[ hi link @namespace Type ]])
       command([[ hi link @function Special ]])
+      command([[ hi @declaration gui=bold ]])
 
       exec_lua(create_server_definition)
       exec_lua([[
@@ -107,9 +110,9 @@ describe('semantic token highlighting', function()
       screen:expect { grid = [[
         #include <iostream>                     |
                                                 |
-        int {3:main}()                              |
+        int {8:main}()                              |
         {                                       |
-            int {2:x};                              |
+            int {7:x};                              |
         #ifdef {5:__cplusplus}                      |
             {4:std}::{2:cout} << {2:x} << "\n";             |
         {6:#else}                                   |
@@ -199,9 +202,9 @@ describe('semantic token highlighting', function()
       screen:expect { grid = [[
         #include <iostream>                     |
                                                 |
-        int {3:main}()                              |
+        int {8:main}()                              |
         {                                       |
-            int {2:x};                              |
+            int {7:x};                              |
         #ifdef {5:__cplusplus}                      |
             {4:std}::{2:cout} << {2:x} << "\n";             |
         {6:#else}                                   |
@@ -228,9 +231,9 @@ describe('semantic token highlighting', function()
       screen:expect { grid = [[
         #include <iostream>                     |
                                                 |
-        int {3:main}()                              |
+        int {8:main}()                              |
         {                                       |
-            int {2:x};                              |
+            int {7:x};                              |
         #ifdef {5:__cplusplus}                      |
             {4:std}::{2:cout} << {2:x} << "\n";             |
         {6:#else}                                   |
@@ -251,9 +254,9 @@ describe('semantic token highlighting', function()
       screen:expect { grid = [[
         #include <iostream>                     |
                                                 |
-        int {3:main}()                              |
+        int {8:main}()                              |
         {                                       |
-            int {2:x};                              |
+            int {7:x};                              |
         #ifdef {5:__cplusplus}                      |
             {4:std}::{2:cout} << {2:x} << "\n";             |
         {6:#else}                                   |
@@ -309,9 +312,9 @@ describe('semantic token highlighting', function()
       screen:expect { grid = [[
         #include <iostream>                     |
                                                 |
-        int {3:main}()                              |
+        int {8:main}()                              |
         {                                       |
-            ^int {3:x}();                            |
+            ^int {8:x}();                            |
         #ifdef {5:__cplusplus}                      |
             {4:std}::{2:cout} << {3:x} << "\n";             |
         {6:#else}                                   |
@@ -489,9 +492,9 @@ describe('semantic token highlighting', function()
       screen:expect { grid = [[
         #include <iostream>                     |
                                                 |
-        int {3:main}()                              |
+        int {8:main}()                              |
         {                                       |
-            int {2:x};                              |
+            int {7:x};                              |
         #ifdef {5:__cplusplus}                      |
             {4:std}::{2:cout} << {2:x} << "\n";             |
         {6:#else}                                   |
@@ -513,9 +516,9 @@ describe('semantic token highlighting', function()
       screen:expect { grid = [[
         #include <iostream>                     |
                                                 |
-        int {3:main}()                              |
+        int {8:main}()                              |
         {                                       |
-            ^int {2:x}();                            |
+            ^int {7:x}();                            |
         #ifdef {5:__cplusplus}                      |
             {4:std}::{2:cout} << {2:x} << "\n";             |
         {6:#else}                                   |