https://github.com/vim-jp/issues/issues/1008 patch to warn when python2 is used in Vim

python2-warn.diff

diff --git a/runtime/doc/if_pyth.txt b/runtime/doc/if_pyth.txt
index 5929bcf..d226bf2 100644
--- a/runtime/doc/if_pyth.txt
+++ b/runtime/doc/if_pyth.txt
@@ -811,5 +811,17 @@ dynamically, these has() calls will try to load them.  If only one can be
 loaded at a time, just checking if Python 2 or 3 are available will prevent
 the other one from being available.
 
+
+							*:py2usingfrom*
+Python 2.x will retire at 2020. (See https://pythonclock.org/).  To help move
+Python 3, vim has a command to detect use of Python 2.x
+
+To see which scripts are using python 2, use `:py2usingfrom` comand: >
+	:py2usingfrom
+	Python 2 is used from these files:
+	  /path/to/your/scirpt/uses/python2a.vim
+	  /path/to/your/scirpt/uses/python2b.vim
+	  /path/to/your/scirpt/uses/python2c.vim
+<
 ==============================================================================
  vim:tw=78:ts=8:ft=help:norl:
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 88dca60..7f4fc04 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -5765,6 +5765,11 @@ A jump table for the options with a short description can be found at |Q_op|.
 	Insert mode completion.  When zero as much space as available is used.
 	|ins-completion-menu|.
 
+						*'py2warn'* *'nopy2warn'*
+'py2warn'		boolean	(default on)
+			global
+	Show a warning at first use of Python 2.x.  See |:py2usingfrom| also.
+
 						*'pythondll'*
 'pythondll'		string	(default depends on the build)
 			global
diff --git a/src/ex_cmds.h b/src/ex_cmds.h
index cb2fadc..bfad5ae 100644
--- a/src/ex_cmds.h
+++ b/src/ex_cmds.h
@@ -1120,6 +1120,9 @@ EX(CMD_pydo,		"pydo",		ex_pydo,
 EX(CMD_pyfile,		"pyfile",	ex_pyfile,
 			RANGE|FILE1|NEEDARG|CMDWIN,
 			ADDR_LINES),
+EX(CMD_py2usingfrom,	"py2usingfrom",	ex_py2usingfrom,
+			TRLBAR|CMDWIN,
+			ADDR_LINES),
 EX(CMD_py3,		"py3",		ex_py3,
 			RANGE|EXTRA|NEEDARG|CMDWIN,
 			ADDR_LINES),
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 295e539..61e709d 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -282,6 +282,7 @@ static void	ex_popup(exarg_T *eap);
 # define ex_python		ex_script_ni
 # define ex_pydo		ex_ni
 # define ex_pyfile		ex_ni
+# define ex_py2usingfrom	ex_ni
 #endif
 #ifndef FEAT_PYTHON3
 # define ex_py3			ex_script_ni
diff --git a/src/globals.h b/src/globals.h
index 0b6abb0..d804d78 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -1653,6 +1653,17 @@ EXTERN int  disable_char_avail_for_testing INIT(= 0);
 EXTERN int  in_free_unref_items INIT(= FALSE);
 #endif
 
+#ifdef FEAT_PYTHON
+/*
+ * State to indicate whether python2 is used and warned.
+ *
+ *  0 - not used.
+ *  1 - used but not warned.
+ *  2 - used and warned.
+ */
+EXTERN int  py2_used INIT(= 0);
+#endif
+
 #ifdef FEAT_TIMERS
 EXTERN int  did_add_timer INIT(= FALSE);
 #endif
diff --git a/src/if_python.c b/src/if_python.c
index 622634d..ba6fe67 100644
--- a/src/if_python.c
+++ b/src/if_python.c
@@ -828,6 +828,54 @@ typedef PySliceObject PySliceObject_T;
  */
 #include "if_py_both.h"
 
+static hashtab_T using_from;
+
+    static void
+mark_py2_used(void)
+{
+    if (py2_used == 0)
+    {
+	py2_used = 1;
+	hash_init(&using_from);
+    }
+    if (sourcing_name != NULL)
+    {
+	hash_T	    hash = hash_hash(sourcing_name);
+	hashitem_T  *hi;
+
+	hi = hash_lookup(&using_from, sourcing_name, hash);
+	if (!HASHITEM_EMPTY(hi))
+	    return;
+	hash_add_item(&using_from, hi, sourcing_name, hash);
+    }
+}
+
+    void
+ex_py2usingfrom(exarg_T *eap)
+{
+    hashtab_T	*ht = &using_from;
+    hashitem_T	*hi;
+    long	todo;
+
+    todo = (long)ht->ht_used;
+    if (todo == 0)
+    {
+	if (py2_used == 0)
+	    msg((char_u *)"Python 2 isn't used yet.");
+	else
+	    msg((char_u *)"Python 2 is used from command line.");
+	return;
+    }
+    msg((char_u *)"Python 2 is used from these files:");
+    for (hi = ht->ht_array; todo > 0; ++hi)
+    {
+	if (!HASHITEM_EMPTY(hi))
+	{
+	    smsg((char_u *)"  %s", hi->hi_key);
+	    --todo;
+	}
+    }
+}
 
 /******************************************************
  * Internal function prototypes.
@@ -878,6 +926,9 @@ python_end(void)
     if (recurse != 0)
 	return;
 
+    if (py2_used != 0)
+	hash_clear_all(&using_from, 0);
+
     ++recurse;
 
 #ifdef DYNAMIC_PYTHON
@@ -1050,6 +1101,8 @@ DoPyCommand(const char *cmd, rangeinitializer init_range, runner run, void *arg)
     if (Python_Init())
 	goto theend;
 
+    mark_py2_used();
+
     init_range(arg);
 
     Python_Release_Vim();	    /* leave vim */
diff --git a/src/main.c b/src/main.c
index f3c471a..a3a92e6 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1078,6 +1078,15 @@ main_loop(
 		 * after insert mode finishes! */
 		need_fileinfo = FALSE;
 	    }
+#ifdef FEAT_PYTHON
+	    if (py2_used == 1)
+	    {
+		if (p_py2warn)
+		    MSG_ATTR("Python 2 is used, check :py2usingfrom for details.",
+			    hl_attr(HLF_W));
+		py2_used = 2;
+	    }
+#endif
 	}
 
 	/* Reset "got_int" now that we got back to the main loop.  Except when
diff --git a/src/option.c b/src/option.c
index 6f9610d..67e075c 100644
--- a/src/option.c
+++ b/src/option.c
@@ -2131,6 +2131,11 @@ static struct vimoption options[] =
 			    (char_u *)NULL, PV_NONE,
 #endif
 			    {(char_u *)0L, (char_u *)0L} SCRIPTID_INIT},
+#ifdef FEAT_PYTHON
+    {"py2warn",	    NULL,   P_BOOL|P_VI_DEF,
+			    (char_u *)&p_py2warn, PV_NONE,
+			    {(char_u *)TRUE, (char_u *)0L} SCRIPTID_INIT},
+#endif
 #if defined(DYNAMIC_PYTHON3)
     {"pythonthreedll",  NULL,   P_STRING|P_EXPAND|P_VI_DEF|P_SECURE,
 			    (char_u *)&p_py3dll, PV_NONE,
diff --git a/src/option.h b/src/option.h
index 0ad2fef..91c0905 100644
--- a/src/option.h
+++ b/src/option.h
@@ -524,6 +524,9 @@ EXTERN char_u	*p_popt;	/* 'printoptions' */
 EXTERN char_u	*p_header;	/* 'printheader' */
 #endif
 EXTERN int	p_prompt;	/* 'prompt' */
+#ifdef FEAT_PYTHON
+EXTERN int	p_py2warn;	/* 'py2warn' */
+#endif
 #ifdef FEAT_GUI
 EXTERN char_u	*p_guifont;	/* 'guifont' */
 # ifdef FEAT_XFONTSET
diff --git a/src/proto/if_python.pro b/src/proto/if_python.pro
index 51054ca..5db6b87 100644
--- a/src/proto/if_python.pro
+++ b/src/proto/if_python.pro
@@ -1,4 +1,5 @@
 /* if_python.c */
+void ex_py2usingfrom(exarg_T *eap);
 int python_enabled(int verbose);
 void python_end(void);
 int python_loaded(void);