feat(treesitter)!: use return values in `language.add()`

Problem: No clear way to check whether parsers are available for a given
language.

Solution: Make `language.add()` return `true` if a parser was
successfully added and `nil` otherwise. Use explicit `assert` instead of
relying on thrown errors.

1 files changed, 3 insertions, 11 deletions

diff --git a/test/functional/treesitter/language_spec.lua b/test/functional/treesitter/language_spec.lua
index 3947ab23b2..e1e34fcecc 100644
--- a/test/functional/treesitter/language_spec.lua
+++ b/test/functional/treesitter/language_spec.lua
@@ -31,29 +31,21 @@ describe('treesitter language API', function()
       )
     )
 
-    eq(false, exec_lua("return pcall(vim.treesitter.language.add, 'borklang')"))
+    eq(NIL, exec_lua("return vim.treesitter.language.add('borklang')"))
 
     eq(
       false,
       exec_lua("return pcall(vim.treesitter.language.add, 'borklang', { path = 'borkbork.so' })")
     )
 
-    eq(
-      ".../language.lua:0: no parser for 'borklang' language, see :help treesitter-parsers",
-      pcall_err(exec_lua, "parser = vim.treesitter.language.inspect('borklang')")
-    )
-
     matches(
       'Failed to load parser: uv_dlsym: .+',
       pcall_err(exec_lua, 'vim.treesitter.language.add("c", { symbol_name = "borklang" })')
     )
   end)
 
-  it('shows error for invalid language name', function()
-    eq(
-      ".../language.lua:0: '/foo/' is not a valid language name",
-      pcall_err(exec_lua, 'vim.treesitter.language.add("/foo/")')
-    )
+  it('does not load parser for invalid language name', function()
+    eq(NIL, exec_lua('vim.treesitter.language.add("/foo/")'))
   end)
 
   it('inspects language', function()