From 7014dacd411abc7647577dde45fc395894ca0023 Mon Sep 17 00:00:00 2001
From: ychampion <ychampion@users.noreply.github.com>
Date: Thu, 9 Jul 2026 08:22:51 +0000
Subject: [PATCH] allow tests to reset dependency cache

Expose mg.ResetDeps for tests that run multiple Mage targets in one process without changing normal once-per-run dependency semantics.

Constraint: Issue #524 needs a way for same-process tests to rerun dependency functions.
Rejected: clearing the cache automatically between Deps calls | that would change normal Mage dependency semantics.
Confidence: high
Scope-risk: narrow
Directive: Do not call ResetDeps while dependencies are running; it only clears the process-global dependency cache.
Tested: go test ./mg -run TestResetDepsAllowsDependenciesToRunAgain -count=1; go test ./mg -count=1; GOPATH="/root/go" go test -vet=all -tags CI -race ./... -count=1; golangci-lint run ./...; git diff --check
Not-tested: full GitHub Actions matrix
---
 mg/deps.go      | 15 +++++++++++++++
 mg/deps_test.go | 19 +++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/mg/deps.go b/mg/deps.go
index bed1a972..baf1bef8 100644
--- a/mg/deps.go
+++ b/mg/deps.go
@@ -44,11 +44,26 @@ func (o *onceMap) LoadOrStore(f Fn) *onceFun {
 	return one
 }
 
+func (o *onceMap) Reset() {
+	o.mu.Lock()
+	defer o.mu.Unlock()
+
+	o.m = map[onceKey]*onceFun{}
+}
+
 var onces = &onceMap{
 	mu: &sync.Mutex{},
 	m:  map[onceKey]*onceFun{},
 }
 
+// ResetDeps clears the dependency cache used by Deps, CtxDeps, SerialDeps, and
+// SerialCtxDeps. It is intended for tests that need to run the same dependencies
+// more than once in a single process. Do not call ResetDeps while dependencies
+// are running.
+func ResetDeps() {
+	onces.Reset()
+}
+
 // SerialDeps is like Deps except it runs each dependency serially, instead of
 // in parallel. This can be useful for resource intensive dependencies that
 // shouldn't be run at the same time.
diff --git a/mg/deps_test.go b/mg/deps_test.go
index fe39bbb2..07aba82e 100644
--- a/mg/deps_test.go
+++ b/mg/deps_test.go
@@ -29,6 +29,25 @@ func TestDepsRunOnce(t *testing.T) {
 	}
 }
 
+func TestResetDepsAllowsDependenciesToRunAgain(t *testing.T) {
+	var calls int64
+	f := func() {
+		atomic.AddInt64(&calls, 1)
+	}
+
+	Deps(f)
+	Deps(f)
+	if calls != 1 {
+		t.Fatalf("expected dependency to run once before reset, ran %d times", calls)
+	}
+
+	ResetDeps()
+	Deps(f)
+	if calls != 2 {
+		t.Fatalf("expected dependency to run again after reset, ran %d times", calls)
+	}
+}
+
 func TestDepsOfDeps(t *testing.T) {
 	ch := make(chan string, 3)
 	// this->f->g->h