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.

2 files changed, 29 insertions, 3 deletions

diff --git a/test/functional/api/vim_spec.lua b/test/functional/api/vim_spec.lua
index f878a50a26..d8914a3ab7 100644
--- a/test/functional/api/vim_spec.lua
+++ b/test/functional/api/vim_spec.lua
@@ -89,6 +89,14 @@ describe('API', function()
 
     it(':verbose set {option}?', function()
       nvim('exec', 'set nowrap', false)
+      eq('nowrap\n\tLast set from anonymous :source',
+        nvim('exec', 'verbose set wrap?', true))
+
+      -- Using script var to force creation of a script item
+      nvim('exec', [[
+        let s:a = 1
+        set nowrap
+      ]], false)
       eq('nowrap\n\tLast set from anonymous :source (script id 1)',
         nvim('exec', 'verbose set wrap?', true))
     end)
@@ -155,6 +163,20 @@ describe('API', function()
           let s:pirate = 'script-scoped varrrrr'
           call nvim_exec('echo s:pirate', 1)
         ]], false))
+
+      -- Script items are created only on script var access
+      eq('1\n0', nvim('exec', [[
+          echo expand("<SID>")->empty()
+          let s:a = 123
+          echo expand("<SID>")->empty()
+        ]], true))
+
+      eq('1\n0', nvim('exec', [[
+          echo expand("<SID>")->empty()
+          function s:a() abort
+          endfunction
+          echo expand("<SID>")->empty()
+        ]], true))
     end)
 
     it('non-ASCII input', function()
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')