instantiated: attach decode function to decoder

instantiated.go

@@ -108,12 +108,10 @@ func (d *InstantiatedDecoder) Drv() iter.Seq[string] {
 	}
 }
 
-// DecodeInstantiated interprets the verbose output of `nix build` and returns a slice of all instantiated derivations.
+// Decode collects and deduplicates derivations emitted by [InstantiatedDecoder].
-func DecodeInstantiated(r io.Reader) ([]string, error) {
+func (d *InstantiatedDecoder) Decode() ([]string, error) {
-	decoder := NewInstantiatedDecoder(r)
-
 	instantiated := make([]string, 0, instantiatedInitialCap)
-	for drv := range decoder.Drv() {
+	for drv := range d.Drv() {
 		if len(instantiated) == cap(instantiated) {
 			// grow the buffer exponentially to minimise copies
 			instantiated = slices.Grow(instantiated, cap(instantiated)<<1)
@@ -122,12 +120,11 @@ func DecodeInstantiated(r io.Reader) ([]string, error) {
 	}
 
 	slices.Sort(instantiated)
-	return slices.Compact(instantiated), decoder.Err()
+	return slices.Compact(instantiated), d.Err()
-
 }
 
 // EvalInstantiated evaluates the installable and returns all derivations instantiated during the evaluation.
-// This relies on verbose output of `nix build` and is certainly not the correct way to do it, but so far it works
+// This interprets verbose output of `nix build` and is certainly not the correct way to do it, but so far it works
 // significantly better than `nix-store -qR` and there does not appear to be a better way.
 func EvalInstantiated(ctx context.Context, installable string) ([]string, error) {
 	c, cancel := context.WithCancel(ctx)
@@ -153,7 +150,7 @@ func EvalInstantiated(ctx context.Context, installable string) ([]string, error)
 		return nil, err
 	}
 
-	instantiated, decodeErr := DecodeInstantiated(stderr)
+	instantiated, decodeErr := NewInstantiatedDecoder(stderr).Decode()
 	waitErr := cmd.Wait()
 	return instantiated, errors.Join(decodeErr, waitErr)
 }

instantiated_test.go

@@ -50,7 +50,7 @@ func TestDecodeInstantiated(t *testing.T) {
 			}
 
 			stderr := strings.NewReader(tc.out)
-			got, err := nixbuild.DecodeInstantiated(stderr)
+			got, err := nixbuild.NewInstantiatedDecoder(stderr).Decode()
 			if !errors.Is(err, tc.wantErr) {
 				t.Fatalf("DecodeInstantiated: error = %v, want %v", err, tc.wantErr)
 			}
@@ -146,7 +146,7 @@ func BenchmarkDecodeInstantiated(b *testing.B) {
 	stderr := strings.NewReader(pluiedevPappardelleOut)
 	var v []string
 	for i := 0; i < b.N; i++ {
-		v, _ = nixbuild.DecodeInstantiated(stderr)
+		v, _ = nixbuild.NewInstantiatedDecoder(stderr).Decode()
 		runtime.KeepAlive(v)
 	}
 }
@@ -155,7 +155,7 @@ func BenchmarkDecodeInstantiatedCopy(b *testing.B) {
 	stderr := strings.NewReader(getchooAtlasOut)
 	var v []string
 	for i := 0; i < b.N; i++ {
-		v, _ = nixbuild.DecodeInstantiated(stderr)
+		v, _ = nixbuild.NewInstantiatedDecoder(stderr).Decode()
 		runtime.KeepAlive(v)
 	}
 }