internal/pkg: optionally force implementation entry

For validation of build determinism.

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

internal/pkg/pkg.go

@@ -6,6 +6,7 @@ import (
 	"bytes"
 	"cmp"
 	"context"
+	"crypto/rand"
 	"crypto/sha512"
 	"encoding/base64"
 	"encoding/binary"
@@ -303,7 +304,7 @@ func (c *common) Open(a Artifact) (r io.ReadCloser, err error) {
 	}
 
 	var pathname *check.Absolute
-	if pathname, _, _, err = c.cache.cure(a, true); err != nil {
+	if pathname, _, _, err = c.cache.cure(a, true, false); err != nil {
 		return
 	}
 
@@ -1633,7 +1634,7 @@ func (c *Cache) Cure(a Artifact) (
 		return
 	}
 
-	pathname, checksum, _, err = c.cure(a, true)
+	pathname, checksum, _, err = c.cure(a, true, false)
 	return
 }
 
@@ -1651,7 +1652,29 @@ func (c *Cache) CureWhence(a Artifact) (
 		return
 	}
 
-	return c.cure(a, true)
+	return c.cure(a, true, false)
+}
+
+// CureNew is like Cure, but always enters the implementation.
+func (c *Cache) CureNew(a Artifact) (
+	pathname *check.Absolute,
+	checksum unique.Handle[Checksum],
+	err error,
+) {
+	c.abortMu.RLock()
+	defer c.abortMu.RUnlock()
+
+	if err = c.toplevel.Load().ctx.Err(); err != nil {
+		return
+	}
+
+	var whence int
+retry:
+	pathname, checksum, whence, err = c.cure(a, true, true)
+	if err != nil || whence == WNew {
+		return
+	}
+	goto retry
 }
 
 // CureError wraps a non-nil error returned attempting to cure an [Artifact].
@@ -2020,13 +2043,19 @@ func WhenceString(whence int) string {
 
 // cure implements Cure without acquiring a read lock on abortMu. cure must not
 // be entered during Abort.
-func (c *Cache) cure(a Artifact, curesExempt bool) (
+func (c *Cache) cure(a Artifact, curesExempt, rebuild bool) (
 	pathname *check.Absolute,
 	checksum unique.Handle[Checksum],
 	whence int,
 	err error,
 ) {
 	id := c.Ident(a)
+	if rebuild {
+		var v ID
+		_, _ = rand.Read(v[:])
+		id = unique.Make(v)
+	}
+
 	ids := Encode(id.Value())
 	pathname = c.base.Append(
 		dirIdentifier,
@@ -2354,7 +2383,7 @@ func (c *Cache) cure(a Artifact, curesExempt bool) (
 			substitutes,
 		)
 
-		if c.flags&CIgnoreSubstitutes == 0 {
+		if !rebuild && c.flags&CIgnoreSubstitutes == 0 {
 			var substituteChecksum unique.Handle[Checksum]
 			substituteChecksum, err = c.loadSubstitute(substitute)
 			if err != nil {
@@ -2419,8 +2448,10 @@ func (c *Cache) cure(a Artifact, curesExempt bool) (
 					return
 				} else if err = externStatus.Close(); err != nil {
 					return
-				} else if err = f.linkSubstitute(ids, substitutes); err != nil {
-					return
+				} else if !rebuild {
+					if err = f.linkSubstitute(ids, substitutes); err != nil {
+						return
+					}
 				}
 			}
 			return
@@ -2432,7 +2463,7 @@ func (c *Cache) cure(a Artifact, curesExempt bool) (
 		err = ca.Cure(&f)
 		c.exitCure(a, curesExempt)
 
-		if err == nil {
+		if !rebuild && err == nil {
 			err = f.linkSubstitute(ids, substitutes)
 		}
 		if err != nil {
@@ -2526,7 +2557,7 @@ func (pending *pendingArtifactDep) cure(c *Cache) {
 	defer pending.Done()
 
 	var err error
-	pending.resP.pathname, pending.resP.checksum, _, err = c.cure(pending.a, false)
+	pending.resP.pathname, pending.resP.checksum, _, err = c.cure(pending.a, false, false)
 	if err == nil {
 		return
 	}