From 8a694e81ff3eedd53657ffa0340e5f509cc9d728 Mon Sep 17 00:00:00 2001
From: Denny Gursky <dennygursky@google.com>
Date: Tue, 21 Jun 2022 21:49:30 -0700
Subject: [PATCH] string builder speed up for Module.String()

---
 internal/addrs/module.go      | 16 +++++++++++++---
 internal/addrs/module_test.go | 14 ++++++++++++++
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/internal/addrs/module.go b/internal/addrs/module.go
index 4ae72b4e42..04ceac7625 100644
--- a/internal/addrs/module.go
+++ b/internal/addrs/module.go
@@ -33,11 +33,21 @@ func (m Module) String() string {
 	if len(m) == 0 {
 		return ""
 	}
-	var steps []string
+	size := 0
 	for _, s := range m {
-		steps = append(steps, "module", s)
+		size += len(s)
 	}
-	return strings.Join(steps, ".")
+	var sb strings.Builder
+	// 8 is len("module.") + len(".")
+	sb.Grow(8*len(m) + size)
+	for i, s := range m {
+		sb.WriteString("module.")
+		sb.WriteString(s)
+		if i != len(m)-1 {
+			sb.WriteString(".")
+		}
+	}
+	return sb.String()
 }
 
 func (m Module) Equal(other Module) bool {
diff --git a/internal/addrs/module_test.go b/internal/addrs/module_test.go
index 829704faf1..86065df4c7 100644
--- a/internal/addrs/module_test.go
+++ b/internal/addrs/module_test.go
@@ -55,3 +55,17 @@ func TestModuleEqual_false(t *testing.T) {
 		})
 	}
 }
+
+func BenchmarkModuleStringShort(b *testing.B) {
+	module := Module{"a", "b"}
+	for n := 0; n < b.N; n++ {
+		module.String()
+	}
+}
+
+func BenchmarkModuleStringLong(b *testing.B) {
+	module := Module{"southamerica-brazil-region", "user-regional-desktop", "user-name"}
+	for n := 0; n < b.N; n++ {
+		module.String()
+	}
+}