feat(:source): reuse SID of sourced buffer

Associate a unique SID for each anonymously :sourced Vim script buffer.
This means sourcing the same buffer will retain the same script-local variables.

Use anonymous :source for memory_usage_spec.lua's "function captures lvars"
test. Use a buffer :source, as the test requires the same SID to be used.
Remove "s:defined_func" logic; it isn't needed, and removing it matches Vim.

src/nvim/ex_cmds2.c

@@ -80,6 +80,7 @@ typedef struct scriptitem_S {
 } scriptitem_T;
 
 static scid_T last_current_SID = 0;
+static int last_current_SID_seq = 0;
 static PMap(scid_T) script_items = MAP_INIT;
 
 /// Sorted growarray of SIDs associated with a :sourced script file.
@@ -1852,7 +1853,8 @@ scid_T script_new_sid(char_u *const fname)
   return sid;
 }
 
-static int source_using_linegetter(void *cookie, LineGetter fgetline, const char *traceback_name)
+static int source_using_linegetter(void *cookie, LineGetter fgetline, const char *traceback_name,
+                                   const scid_T sid)
 {
   char_u *save_sourcing_name = sourcing_name;
   linenr_T save_sourcing_lnum = sourcing_lnum;
@@ -1868,15 +1870,13 @@ static int source_using_linegetter(void *cookie, LineGetter fgetline, const char
   sourcing_lnum = 0;
 
   const sctx_T save_current_sctx = current_sctx;
-  if (current_sctx.sc_sid != SID_LUA) {
-    current_sctx.sc_sid = ++last_current_SID;
-  }
-  current_sctx.sc_seq = 0;
+  current_sctx.sc_sid = sid;
+  current_sctx.sc_seq = sid > 0 ? ++last_current_SID_seq : 0;
   current_sctx.sc_lnum = save_sourcing_lnum;
   funccal_entry_T entry;
   save_funccal(&entry);
-  int retval = do_cmdline(NULL, fgetline, cookie,
-                          DOCMD_VERBOSE | DOCMD_NOWAIT | DOCMD_REPEAT);
+  const int retval = do_cmdline(NULL, fgetline, cookie,
+                                DOCMD_VERBOSE | DOCMD_NOWAIT | DOCMD_REPEAT);
   sourcing_lnum = save_sourcing_lnum;
   sourcing_name = save_sourcing_name;
   current_sctx = save_current_sctx;
@@ -1887,6 +1887,8 @@ static int source_using_linegetter(void *cookie, LineGetter fgetline, const char
 static void cmd_source_buffer(const exarg_T *const eap)
   FUNC_ATTR_NONNULL_ALL
 {
+  static Map(handle_T, scid_T) buf_sids = MAP_INIT;
+
   if (curbuf == NULL) {
     return;
   }
@@ -1907,13 +1909,16 @@ static void cmd_source_buffer(const exarg_T *const eap)
     .buf = ga.ga_data,
     .offset = 0,
   };
-  if (curbuf->b_fname
-      && path_with_extension((const char *)curbuf->b_fname, "lua")) {
-    nlua_source_using_linegetter(get_str_line, (void *)&cookie,
-                                 ":source (no file)");
+  if (curbuf->b_fname && path_with_extension((const char *)curbuf->b_fname, "lua")) {
+    nlua_source_using_linegetter(get_str_line, (void *)&cookie, ":source (no file)");
   } else {
-    source_using_linegetter((void *)&cookie, get_str_line,
-                            ":source (no file)");
+    scid_T sid = map_get(handle_T, scid_T)(&buf_sids, curbuf->handle);
+    if (sid == 0) {
+      // First time sourcing this buffer, use a new SID for it.
+      sid = ++last_current_SID;
+      map_put(handle_T, scid_T)(&buf_sids, curbuf->handle, sid);
+    }
+    source_using_linegetter((void *)&cookie, get_str_line, ":source (no file)", sid);
   }
   ga_clear(&ga);
 }
@@ -1927,7 +1932,8 @@ int do_source_str(const char *cmd, const char *traceback_name)
     .buf = (char_u *)cmd,
     .offset = 0,
   };
-  return source_using_linegetter((void *)&cookie, get_str_line, traceback_name);
+  const scid_T sid = current_sctx.sc_sid == SID_LUA ? SID_LUA : ++last_current_SID;
+  return source_using_linegetter((void *)&cookie, get_str_line, traceback_name, sid);
 }
 
 /// When fname is a 'lua' file nlua_exec_file() is invoked to source it.
@@ -2194,8 +2200,6 @@ int do_source(char *fname, int check_other, int is_vimrc)
 static scriptitem_T *new_file_sctx(char_u *fname, sctx_T *ret_sctx)
   FUNC_ATTR_NONNULL_ARG(1)
 {
-  static int last_current_SID_seq = 0;
-
   sctx_T script_sctx = { .sc_seq = ++last_current_SID_seq,
                          .sc_lnum = 0,
                          .sc_sid = 0 };

src/nvim/map.c

@@ -175,6 +175,7 @@ MAP_IMPL(uint64_t, ssize_t, SSIZE_INITIALIZER)
 MAP_IMPL(uint64_t, uint64_t, DEFAULT_INITIALIZER)
 MAP_IMPL(uint32_t, uint32_t, DEFAULT_INITIALIZER)
 MAP_IMPL(handle_T, ptr_t, DEFAULT_INITIALIZER)
+MAP_IMPL(handle_T, scid_T, DEFAULT_INITIALIZER)
 MAP_IMPL(scid_T, ptr_t, DEFAULT_INITIALIZER)
 #define MSGPACK_HANDLER_INITIALIZER { .fn = NULL, .fast = false }
 MAP_IMPL(String, MsgpackRpcRequestHandler, MSGPACK_HANDLER_INITIALIZER)

src/nvim/map.h

@@ -45,6 +45,7 @@ MAP_DECLS(uint64_t, uint64_t)
 MAP_DECLS(uint32_t, uint32_t)
 
 MAP_DECLS(handle_T, ptr_t)
+MAP_DECLS(handle_T, scid_T)
 MAP_DECLS(scid_T, ptr_t)
 MAP_DECLS(String, MsgpackRpcRequestHandler)
 MAP_DECLS(HlEntry, int)

test/functional/ex_cmds/source_spec.lua

@@ -64,16 +64,47 @@ 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')
-    eq('Vim(echo):E117: Unknown function: s:C', exc_exec('echo D()'))
+    eq("<SNR>1_C()", meths.exec('echo D()', true))
 
     exec('set cpoptions+=C')
     eq('Vim(let):E15: Invalid expression: #{', exc_exec("'<,'>source"))
   end)
 
+  it('current buffer reuses SID', function()
+    insert [[
+      " also shouldn't cause a redefinition error when `:source`ing the
+      " same buffer twice (script context uses a new sequence number)
+      func s:Foo()
+      endfunc
+      let id = expand("<SID>")
+    ]]
+    command('source')
+    eq("<SNR>1_", eval('g:id'))
+    command('source')
+    eq("<SNR>1_", eval('g:id'))
+
+    -- Ensure a new buffer has a different SID
+    command('new')
+    insert [[
+      let id = expand("<SID>")
+    ]]
+    command('source')
+    eq("<SNR>2_", eval('g:id'))
+    command('source')
+    eq("<SNR>2_", eval('g:id'))
+
+    command('wincmd p')
+    command('source')
+    eq("<SNR>1_", eval('g:id'))
+
+    -- Scripts should be anonymous
+    eq("", exec_capture(':scriptnames'))
+  end)
+
   it('does not break if current buffer is modified while sourced', function()
     insert [[
       bwipeout!

test/functional/legacy/memory_usage_spec.lua

@@ -10,7 +10,7 @@ local source = helpers.source
 local poke_eventloop = helpers.poke_eventloop
 local uname = helpers.uname
 local load_adjust = helpers.load_adjust
-local write_file = helpers.write_file
+local insert = helpers.insert
 local isCI = helpers.isCI
 
 local function isasan()
@@ -85,12 +85,6 @@ setmetatable(monitor_memory_usage,
 end})
 
 describe('memory usage', function()
-  local tmpfile = 'X_memory_usage'
-
-  after_each(function()
-    os.remove(tmpfile)
-  end)
-
   local function check_result(tbl, status, result)
     if not status then
       print('')
@@ -143,23 +137,21 @@ describe('memory usage', function()
   it('function capture lvars', function()
     local pid = eval('getpid()')
     local before = monitor_memory_usage(pid)
-    write_file(tmpfile, [[
-      if !exists('s:defined_func')
-        func s:f()
-          let x = l:
-        endfunc
-      endif
-      let s:defined_func = 1
+    -- :source from a buffer so that the same SID is used.
+    insert([[
+      func s:f()
+        let x = l:
+      endfunc
       for _ in range(10000)
         call s:f()
       endfor
     ]])
-    feed_command('source '..tmpfile)
+    feed_command("source")
     poke_eventloop()
     local after = monitor_memory_usage(pid)
     for _ = 1, 3 do
       -- TODO: check_result fails if command() is used here. Why? #16064
-      feed_command('source '..tmpfile)
+      feed_command("source")
       poke_eventloop()
     end
     local last = monitor_memory_usage(pid)