internal/pkg: cache computed identifiers

This eliminates duplicate identifier computations. The new implementation also significantly reduces allocations while computing identifier for a large dependency tree.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/tar_test.go

@@ -101,8 +101,11 @@ func checkTarHTTP(
 		h.Write([]byte{byte(pkg.KindTar), 0, 0, 0, 0, 0, 0, 0})
 		h.Write([]byte{pkg.TarGzip, 0, 0, 0, 0, 0, 0, 0})
 		h.Write([]byte{byte(pkg.KindHTTPGet), 0, 0, 0, 0, 0, 0, 0})
-		httpIdent := pkg.KindHTTPGet.Ident([]byte("file:///testdata"))
-		h.Write(httpIdent[:])
+
+		h0 := sha512.New384()
+		h0.Write([]byte{byte(pkg.KindHTTPGet), 0, 0, 0, 0, 0, 0, 0})
+		h0.Write([]byte("file:///testdata"))
+		h.Write(h0.Sum(nil))
 		return pkg.ID(h.Sum(nil))
 	}()
 
@@ -113,10 +116,6 @@ func checkTarHTTP(
 		pkg.TarGzip,
 	)
 
-	if id := pkg.Ident(a); id != wantIdent {
-		t.Fatalf("Ident: %s, want %s", pkg.Encode(id), pkg.Encode(wantIdent))
-	}
-
 	tarDir := stubArtifact{
 		kind:   pkg.KindExec,
 		params: []byte("directory containing a single regular file"),
@@ -164,9 +163,9 @@ func checkTarHTTP(
 		},
 	}
 	// destroy these to avoid including it in flatten test case
-	defer newDestroyArtifactFunc(tarDir)(t, base, c)
-	defer newDestroyArtifactFunc(tarDirMulti)(t, base, c)
-	defer newDestroyArtifactFunc(tarDirType)(t, base, c)
+	defer newDestroyArtifactFunc(&tarDir)(t, base, c)
+	defer newDestroyArtifactFunc(&tarDirMulti)(t, base, c)
+	defer newDestroyArtifactFunc(&tarDirType)(t, base, c)
 
 	cureMany(t, c, []cureStep{
 		{"file", a, base.Append(
@@ -175,25 +174,25 @@ func checkTarHTTP(
 		), wantChecksum, nil},
 
 		{"directory", pkg.NewTar(
-			tarDir,
+			&tarDir,
 			pkg.TarGzip,
 		), ignorePathname, wantChecksum, nil},
 
 		{"multiple entries", pkg.NewTar(
-			tarDirMulti,
+			&tarDirMulti,
 			pkg.TarGzip,
 		), nil, pkg.Checksum{}, errors.New(
 			"input directory does not contain a single regular file",
 		)},
 
 		{"bad type", pkg.NewTar(
-			tarDirType,
+			&tarDirType,
 			pkg.TarGzip,
 		), nil, pkg.Checksum{}, errors.New(
 			"input directory does not contain a single regular file",
 		)},
 
-		{"error passthrough", pkg.NewTar(stubArtifact{
+		{"error passthrough", pkg.NewTar(&stubArtifact{
 			kind:   pkg.KindExec,
 			params: []byte("doomed artifact"),
 			cure: func(t *pkg.TContext) error {