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/exec.go

@@ -2,7 +2,6 @@ package pkg
 
 import (
 	"bufio"
-	"bytes"
 	"context"
 	"errors"
 	"fmt"
@@ -101,8 +100,9 @@ func (a *execNetArtifact) Checksum() Checksum { return a.checksum }
 func (a *execNetArtifact) Kind() Kind { return KindExecNet }
 
 // Params is [Checksum] concatenated with [KindExec] params.
-func (a *execNetArtifact) Params() []byte {
-	return slices.Concat(a.checksum[:], a.execArtifact.Params())
+func (a *execNetArtifact) Params(ctx *IContext) {
+	ctx.GetHash().Write(a.checksum[:])
+	a.execArtifact.Params(ctx)
 }
 
 // Cure cures the [Artifact] in the container described by the caller. The
@@ -165,40 +165,40 @@ func NewExec(
 // Kind returns the hardcoded [Kind] constant.
 func (a *execArtifact) Kind() Kind { return KindExec }
 
-// Params returns paths, executable pathname and args concatenated together.
-func (a *execArtifact) Params() []byte {
-	var buf bytes.Buffer
+// Params writes paths, executable pathname and args.
+func (a *execArtifact) Params(ctx *IContext) {
+	h := ctx.GetHash()
+
+	_0, _1 := []byte{0}, []byte{1}
 	for _, p := range a.paths {
 		if p.W {
-			buf.WriteByte(1)
+			h.Write(_1)
 		} else {
-			buf.WriteByte(0)
+			h.Write(_0)
 		}
 		if p.P != nil {
-			buf.WriteString(p.P.String())
+			h.Write([]byte(p.P.String()))
 		} else {
-			buf.WriteString("invalid P\x00")
+			h.Write([]byte("invalid P\x00"))
 		}
-		buf.WriteByte(0)
+		h.Write(_0)
 		for _, d := range p.A {
-			id := Ident(d)
-			buf.Write(id[:])
+			ctx.WriteIdent(d)
 		}
-		buf.WriteByte(0)
+		h.Write(_0)
 	}
-	buf.WriteByte(0)
-	buf.WriteString(a.dir.String())
-	buf.WriteByte(0)
+	h.Write(_0)
+	h.Write([]byte(a.dir.String()))
+	h.Write(_0)
 	for _, e := range a.env {
-		buf.WriteString(e)
+		h.Write([]byte(e))
 	}
-	buf.WriteByte(0)
-	buf.WriteString(a.path.String())
-	buf.WriteByte(0)
+	h.Write(_0)
+	h.Write([]byte(a.path.String()))
+	h.Write(_0)
 	for _, arg := range a.args {
-		buf.WriteString(arg)
+		h.Write([]byte(arg))
 	}
-	return buf.Bytes()
 }
 
 // Dependencies returns a slice of all artifacts collected from caller-supplied