lua: simple snippet support in the completion items (#12118)

Old behavior is: foo(${placeholder: bar, ...)

with lots of random garbage you'd never want inserted.

New behavior is: foo(bar, baz) 

(which maybe is good, maybe is bad [depends on user], but definitely better than it was).

-----

* Implement rudimentary snippet parsing

Add support for parsing and discarding snippet tokens from the completion items.

Fixes #11982

* Enable snippet support

* Functional tests for snippet parsing

Add simplified real-world snippet text examples to the completion items
test

* Add a test for nested snippet tokens

* Remove TODO comment

* Return the unmodified item if the format is plain text

* Add a plain text completion item

1 files changed, 12 insertions, 1 deletions

diff --git a/test/functional/plugin/lsp_spec.lua b/test/functional/plugin/lsp_spec.lua
index e39511d0ea..f1478c782d 100644
--- a/test/functional/plugin/lsp_spec.lua
+++ b/test/functional/plugin/lsp_spec.lua
@@ -973,7 +973,14 @@ describe('LSP', function()
         { label='foocar', insertText='foobar', textEdit={} },
         -- resolves into textEdit.newText
         { label='foocar', insertText='foodar', textEdit={newText='foobar'} },
-        { label='foocar', textEdit={newText='foobar'} }
+        { label='foocar', textEdit={newText='foobar'} },
+        -- real-world snippet text
+        { label='foocar', insertText='foodar', textEdit={newText='foobar(${1:place holder}, ${2:more ...holder{\\}})'} },
+        { label='foocar', insertText='foodar(${1:var1} typ1, ${2:var2} *typ2) {$0\\}', textEdit={} },
+        -- nested snippet tokens
+        { label='foocar', insertText='foodar(${1:var1 ${2|typ2,typ3|} ${3:tail}}) {$0\\}', textEdit={} },
+        -- plain text
+        { label='foocar', insertText='foodar(${1:var1})', insertTextFormat=1, textEdit={} },
       }
       local completion_list_items = {items=completion_list}
       local expected = {
@@ -983,6 +990,10 @@ describe('LSP', function()
         { abbr = 'foocar', dup = 1, empty = 1, icase = 1, info = ' ', kind = 'Unknown', menu = '', word = 'foobar', user_data = { nvim = { lsp = { completion_item = { label='foocar', insertText='foobar', textEdit={} } } } } },
         { abbr = 'foocar', dup = 1, empty = 1, icase = 1, info = ' ', kind = 'Unknown', menu = '', word = 'foobar', user_data = { nvim = { lsp = { completion_item = { label='foocar', insertText='foodar', textEdit={newText='foobar'} } } } } },
         { abbr = 'foocar', dup = 1, empty = 1, icase = 1, info = ' ', kind = 'Unknown', menu = '', word = 'foobar', user_data = { nvim = { lsp = { completion_item = { label='foocar', textEdit={newText='foobar'} } } } } },
+        { abbr = 'foocar', dup = 1, empty = 1, icase = 1, info = ' ', kind = 'Unknown', menu = '', word = 'foobar(place holder, more ...holder{})', user_data = { nvim = { lsp = { completion_item = { label='foocar', insertText='foodar', textEdit={newText='foobar(${1:place holder}, ${2:more ...holder{\\}})'} } } } } },
+        { abbr = 'foocar', dup = 1, empty = 1, icase = 1, info = ' ', kind = 'Unknown', menu = '', word = 'foodar(var1 typ1, var2 *typ2) {}', user_data = { nvim = { lsp = { completion_item = { label='foocar', insertText='foodar(${1:var1} typ1, ${2:var2} *typ2) {$0\\}', textEdit={} } } } } },
+        { abbr = 'foocar', dup = 1, empty = 1, icase = 1, info = ' ', kind = 'Unknown', menu = '', word = 'foodar(var1 typ2,typ3 tail) {}', user_data = { nvim = { lsp = { completion_item = { label='foocar', insertText='foodar(${1:var1 ${2|typ2,typ3|} ${3:tail}}) {$0\\}', textEdit={} } } } } },
+        { abbr = 'foocar', dup = 1, empty = 1, icase = 1, info = ' ', kind = 'Unknown', menu = '', word = 'foodar(${1:var1})', user_data = { nvim = { lsp = { completion_item = { label='foocar', insertText='foodar(${1:var1})', insertTextFormat=1, textEdit={} } } } } },
       }
 
       eq(expected, exec_lua([[return vim.lsp.util.text_document_completion_list_to_complete_items(...)]], completion_list, prefix))