From fed124f1460226ab037657bac5717bdb49bf6b78 Mon Sep 17 00:00:00 2001
From: Sergey Matveev <stargrave@stargrave.org>
Date: Tue, 17 Jan 2023 11:46:33 +0300
Subject: [PATCH] Fix simultaneous duplicate always-ed target run

---
 doc/news.texi                   |  7 ++++++
 ifchange.go                     | 12 +++++++----
 t/goredo-double-consideration.t | 38 +++++++++++++++++++++++++++++++++
 usage.go                        |  2 +-
 4 files changed, 54 insertions(+), 5 deletions(-)
 create mode 100755 t/goredo-double-consideration.t

diff --git a/doc/news.texi b/doc/news.texi
index 9786d10..a5b5b35 100644
--- a/doc/news.texi
+++ b/doc/news.texi
@@ -2,6 +2,13 @@
 @cindex news
 @unnumbered News
 
+@anchor{Release 1_29_0}
+@section Release 1.29.0
+@itemize
+@item
+    Fix possible error when two always-ed targets are run simultaneously.
+@end itemize
+
 @anchor{Release 1_28_0}
 @section Release 1.28.0
 @itemize
diff --git a/ifchange.go b/ifchange.go
index dc5b9da..cbf1c05 100644
--- a/ifchange.go
+++ b/ifchange.go
@@ -98,7 +98,7 @@ func buildDependants(tgts []string) map[string]struct{} {
 		}
 	}
 	if len(seen) == 0 {
-		return nil
+		return seen
 	}
 
 	levelOrig := Level
@@ -135,17 +135,18 @@ func buildDependants(tgts []string) map[string]struct{} {
 
 RebuildDeps:
 	tracef(CDebug, "checking %d dependant targets: %v", len(queueSrc), queueSrc)
-	queue := []string{}
+	queue := map[string]struct{}{}
 	for _, tgt := range queueSrc {
 		for dep := range deps[tgt] {
-			queue = append(queue, dep)
+			queue[dep] = struct{}{}
 		}
 	}
+
 	tracef(CDebug, "building %d dependant targets: %v", len(queue), queue)
 	errs = make(chan error, len(queue))
 	jobs := 0
 	queueSrc = []string{}
-	for _, tgt := range queue {
+	for tgt, _ := range queue {
 		ood, err := isOODWithTrace(Cwd, tgt, 0, seen)
 		if err != nil {
 			tracef(CErr, "dependant error: %s, skipping dependants", err)
@@ -196,6 +197,9 @@ func ifchange(tgts []string, forced, traced bool) (bool, error) {
 	}
 	defer Jobs.Wait()
 	seen := buildDependants(tgts)
+	if seen == nil {
+		return false, nil
+	}
 	oodTgtsClear()
 	tracef(CDebug, "building %d targets: %v", len(tgts), tgts)
 	jobs := 0
diff --git a/t/goredo-double-consideration.t b/t/goredo-double-consideration.t
new file mode 100755
index 0000000..b300245
--- /dev/null
+++ b/t/goredo-double-consideration.t
@@ -0,0 +1,38 @@
+#!/bin/sh
+
+testname=`basename "$0"`
+test_description="Do not fail if two always-ed targets run simultaneously"
+. $SHARNESS_TEST_SRCDIR/sharness.sh
+export REDO_TOP_DIR="`pwd`" REDO_NO_PROGRESS=1
+
+echo redo-ifchange version.h > all.do
+cat > version.h.do <<EOF
+redo-ifchange date version version.h.in
+VERSION=\$(cat version)
+DATE=\$(cat date)
+cat "\$2".in |
+    sed -e "s/%%VERSION%%/\${VERSION}/g" \
+        -e "s/%%DATE%%/\${DATE}/g" \
+       > "\$3"
+redo-stamp <"\$3"
+EOF
+cat > version.do <<EOF
+git rev-parse --short HEAD > "\$3"
+redo-always
+redo-stamp <"\$3"
+EOF
+cat > date.do <<EOF
+date +'%Y%m%d_%H%M%S' >"\$3"
+redo-always
+redo-stamp <"\$3"
+EOF
+cat > version.h.in <<EOF
+#define PRJ_VERSION "%%VERSION%%"
+#define PRJ_BLDDATE "%%DATE%%"
+EOF
+
+test_expect_success "first run is successful" redo
+sleep 1
+test_expect_success "second run is successful" redo
+
+test_done
diff --git a/usage.go b/usage.go
index 192761c..ec46d58 100644
--- a/usage.go
+++ b/usage.go
@@ -24,7 +24,7 @@ import (
 )
 
 const (
-	Version  = "1.28.0"
+	Version  = "1.29.0"
 	Warranty = `Copyright (C) 2020-2023 Sergey Matveev
 
 This program is free software: you can redistribute it and/or modify
-- 
2.44.0