From 64e7c548843c7938fcfa6b697108d28aa26f4d69 Mon Sep 17 00:00:00 2001
From: Ryan Prior <4389854+ryanprior@users.noreply.github.com>
Date: Thu, 31 Dec 2020 02:31:38 -0600
Subject: [PATCH] v.util: accomodate reproducible build environments like guix,
 by not recompiling cmd/tools when mtime < 1024 (#7702)

---
 vlib/v/util/util.v | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/vlib/v/util/util.v b/vlib/v/util/util.v
index 811b71585b..1ed32bacfa 100644
--- a/vlib/v/util/util.v
+++ b/vlib/v/util/util.v
@@ -179,7 +179,10 @@ pub fn should_recompile_tool(vexe string, tool_source string) bool {
 	if !os.exists(tool_exe) {
 		should_compile = true
 	} else {
-		if os.file_last_mod_unix(tool_exe) <= os.file_last_mod_unix(vexe) {
+		mtime_vexe := os.file_last_mod_unix(vexe)
+		mtime_tool_exe := os.file_last_mod_unix(tool_exe)
+		mtime_tool_source := os.file_last_mod_unix(tool_source)
+		if mtime_tool_exe <= mtime_vexe {
 			// v was recompiled, maybe after v up ...
 			// rebuild the tool too just in case
 			should_compile = true
@@ -192,10 +195,19 @@ pub fn should_recompile_tool(vexe string, tool_source string) bool {
 				should_compile = false
 			}
 		}
-		if os.file_last_mod_unix(tool_exe) <= os.file_last_mod_unix(tool_source) {
+		if mtime_tool_exe <= mtime_tool_source {
 			// the user changed the source code of the tool, or git updated it:
 			should_compile = true
 		}
+		// GNU Guix and possibly other environments, have bit for bit reproducibility in mind,
+		// including filesystem attributes like modification times, so they set the modification
+		// times of executables to a small number like 0, 1 etc. In this case, we should not
+		// recompile even if other heuristics say that we should. Users in such environments,
+		// have to explicitly do: `v cmd/tools/vfmt.v`, and/or install v from source, and not
+		// use the system packaged one, if they desire to develop v itself.
+		if mtime_vexe < 1024 && mtime_tool_exe < 1024 {
+			should_compile = false
+		}
 	}
 	return should_compile
 }