feat(:source, nvim_exec): defer script item creation until s:var access

For anonymous scripts, defer the creation of script items until an attempt to access a script-local
variable is made. This dramatically reduces the number of script items created when using lots of
vim.cmd and nvim_exec especially.

This will mean <SID> usage fails until a script-local variable access is first made.

1 files changed, 7 insertions, 3 deletions

diff --git a/test/functional/ex_cmds/source_spec.lua b/test/functional/ex_cmds/source_spec.lua
index 8077b22e56..fa650d611b 100644
--- a/test/functional/ex_cmds/source_spec.lua
+++ b/test/functional/ex_cmds/source_spec.lua
@@ -26,13 +26,17 @@ describe(':source', function()
         \ k: "v"
        "\ (o_o)
         \ }
+      let c = expand("<SID>")->empty()
       let s:s = 0zbeef.cafe
-      let c = s:s]])
+      let d = s:s]])
 
     command('source')
     eq('2', meths.exec('echo a', true))
     eq("{'k': 'v'}", meths.exec('echo b', true))
-    eq("0zBEEFCAFE", meths.exec('echo c', true))
+
+    -- Script items are created only on script var access
+    eq("1", meths.exec('echo c', true))
+    eq("0zBEEFCAFE", meths.exec('echo d', true))
 
     exec('set cpoptions+=C')
     eq('Vim(let):E15: Invalid expression: #{', exc_exec('source'))
@@ -62,7 +66,7 @@ describe(':source', function()
     feed_command(':source')
     eq('4', meths.exec('echo a', true))
     eq("{'K': 'V'}", meths.exec('echo b', true))
-    eq("<SNR>3_C()", meths.exec('echo D()', true))
+    eq("<SNR>1_C()", meths.exec('echo D()', true))
 
     -- Source last line only
     feed_command(':$source')