fix(lua): always use vim.inspect() for :lua= (#32715)

runtime/doc/lua.txt

@@ -289,7 +289,7 @@ arguments separated by " " (space) instead of "\t" (tab).
 :lua {chunk}
     Executes Lua chunk {chunk}. If {chunk} starts with "=" the rest of the
     chunk is evaluated as an expression and printed. `:lua =expr` and `:=expr`
-    are equivalent to `:lua vim.print(expr)`.
+    are equivalent to `:lua print(vim.inspect(expr))`.
 
     Examples: >vim
         :lua vim.api.nvim_command('echo "Hello, Nvim!"')

runtime/lua/vim/_editor.lua

@@ -1142,6 +1142,21 @@ do
   end
 end
 
+--- @param inspect_strings boolean use vim.inspect() for strings
+function vim._print(inspect_strings, ...)
+  local msg = {}
+  for i = 1, select('#', ...) do
+    local o = select(i, ...)
+    if not inspect_strings and type(o) == 'string' then
+      table.insert(msg, o)
+    else
+      table.insert(msg, vim.inspect(o, { newline = '\n', indent = '  ' }))
+    end
+  end
+  print(table.concat(msg, '\n'))
+  return ...
+end
+
 --- "Pretty prints" the given arguments and returns them unmodified.
 ---
 --- Example:
@@ -1155,17 +1170,7 @@ end
 --- @param ... any
 --- @return any # given arguments.
 function vim.print(...)
-  local msg = {}
-  for i = 1, select('#', ...) do
-    local o = select(i, ...)
-    if type(o) == 'string' then
-      table.insert(msg, o)
-    else
-      table.insert(msg, vim.inspect(o, { newline = '\n', indent = '  ' }))
-    end
-  end
-  print(table.concat(msg, '\n'))
-  return ...
+  return vim._print(false, ...)
 end
 
 --- Translates keycodes.

src/nvim/lua/executor.c

@@ -1668,13 +1668,13 @@ void ex_lua(exarg_T *const eap)
 
   // ":lua {code}", ":={expr}" or ":lua ={expr}"
   //
-  // When "=expr" is used transform it to "vim.print(expr)".
+  // When "=expr" is used transform it to "vim._print(true, expr)".
   if (eap->cmdidx == CMD_equal || code[0] == '=') {
     size_t off = (eap->cmdidx == CMD_equal) ? 0 : 1;
-    len += sizeof("vim.print()") - 1 - off;
+    len += sizeof("vim._print(true, )") - 1 - off;
     // `nlua_typval_exec` doesn't expect NUL-terminated string so `len` must end before NUL byte.
     char *code_buf = xmallocz(len);
-    vim_snprintf(code_buf, len + 1, "vim.print(%s)", code + off);
+    vim_snprintf(code_buf, len + 1, "vim._print(true, %s)", code + off);
     xfree(code);
     code = code_buf;
   }

test/functional/lua/commands_spec.lua

@@ -173,8 +173,13 @@ describe(':lua', function()
     exec_lua('x = 5')
     eq('5', exec_capture(':lua =x'))
     eq('5', exec_capture('=x'))
+    exec_lua('x = "5"')
+    eq('"5"', exec_capture(':lua =x'))
+    eq('"5"', exec_capture('=x'))
     exec_lua("function x() return 'hello' end")
-    eq('hello', exec_capture(':lua = x()'))
+    eq('"hello"', exec_capture(':lua = x()'))
+    exec_lua("function x() return 'hello ' end")
+    eq('"hello "', exec_capture(':lua = x()'))
     exec_lua('x = {a = 1, b = 2}')
     eq('{\n  a = 1,\n  b = 2\n}', exec_capture(':lua  =x'))
     exec_lua(function()
@@ -189,14 +194,14 @@ describe(':lua', function()
     eq(
       dedent [[
       true
-      Return value]],
+      "Return value"]],
       exec_capture(':lua  =x(true)')
     )
     eq(
       dedent [[
       false
       nil
-      Error message]],
+      "Error message"]],
       exec_capture('=x(false)')
     )
   end)