avoid memory leak; add test for zero allocations for Compare calls

Author: gburt

collate/collate.go

@@ -108,10 +108,12 @@ func (b *Buffer) Reset() {
 // a new buffer will be allocated for each call.
 func (c *Collator) Compare(a, b []byte) int {
 	var (
-		kA = c.Key(&c.buf, a)
-		kB = c.Key(&c.buf, b)
+		kA  = c.Key(&c.buf, a)
+		kB  = c.Key(&c.buf, b)
+		ret = bytes.Compare(kA, kB)
 	)
-	return bytes.Compare(kA, kB)
+	c.buf.Reset()
+	return ret
 }
 
 // CompareString returns an integer comparing the two strings.
@@ -120,10 +122,12 @@ func (c *Collator) Compare(a, b []byte) int {
 // a new buffer will be allocated for each call.
 func (c *Collator) CompareString(a, b string) int {
 	var (
-		kA = c.KeyFromString(&c.buf, a)
-		kB = c.KeyFromString(&c.buf, b)
+		kA  = c.KeyFromString(&c.buf, a)
+		kB  = c.KeyFromString(&c.buf, b)
+		ret = bytes.Compare(kA, kB)
 	)
-	return bytes.Compare(kA, kB)
+	c.buf.Reset()
+	return ret
 }
 
 // Key returns the collation key for str.

collate/collate_test.go

@@ -6,6 +6,7 @@ package collate
 
 import (
 	"bytes"
+	"runtime"
 	"testing"
 
 	"golang.org/x/text/internal/colltab"
@@ -470,6 +471,32 @@ func TestKeyFromStringCompareForShiftTrimmed(t *testing.T) {
 	}
 }
 
+func totalAllocs() uint64 {
+	var mem runtime.MemStats
+	runtime.ReadMemStats(&mem)
+	return mem.TotalAlloc
+}
+
+func TestNoAllocationsForCompares(t *testing.T) {
+	var a = []byte("foo")
+	var b = []byte("bar")
+	var c = New(language.MustParse("en-us-u-ka-posix-ks-level4"))
+	var before = totalAllocs()
+
+	for i := 0; i < 100; i++ {
+		c.CompareString("foo", "bar")
+		c.Compare(a, b)
+	}
+
+	var bytesAllocated = totalAllocs() - before
+
+	// We should allocate zero additional bytes b/c the Buffer has 4k of memory pre-allocated that
+	// we should re-use for each/every key we generate for the comparisons.
+	if bytesAllocated != 0 {
+		t.Errorf("Expected CompareStrings to not allocate memory but it allocated %v", bytesAllocated)
+	}
+}
+
 func TestNumeric(t *testing.T) {
 	c := New(language.English, Loose, Numeric)