instantiated: parse instantiated messages

instantiated.go

@@ -0,0 +1,128 @@
+package nixbuild
+
+import (
+	"bufio"
+	"context"
+	"errors"
+	"io"
+	"os/exec"
+	"path"
+	"slices"
+	"strings"
+)
+
+const (
+	instantiatedPrefix    = "instantiated '"
+	instantiatedSeparator = " -> "
+	instantiatedFields    = 2
+
+	// a reasonable starting buffer capacity: pretty close to average of test cases
+	instantiatedInitialCap = 1 << 13
+)
+
+const (
+	InstantiatedBadFields = iota
+	InstantiatedUnexpectedQuotes
+	InstantiatedNotAbsolute
+)
+
+type MalformedInstantiatedError struct {
+	Message string
+	Type    int
+}
+
+func (m *MalformedInstantiatedError) Error() string {
+	switch m.Type {
+	case InstantiatedBadFields:
+		return "incorrect amount of fields in instantiated message"
+	case InstantiatedUnexpectedQuotes:
+		return "unexpected quotes in final instantiated field"
+	case InstantiatedNotAbsolute:
+		return "instantiated derivation path is not absolute"
+	default:
+		panic("unreachable")
+	}
+}
+
+func (m *MalformedInstantiatedError) Is(err error) bool {
+	var e *MalformedInstantiatedError
+	if !errors.As(err, &e) {
+		return false
+	}
+	if e == nil || m == nil {
+		return e == m
+	}
+	return e.Type == m.Type
+}
+
+// DecodeInstantiated interprets the verbose output of `nix build` and returns a slice of all instantiated derivations.
+func DecodeInstantiated(stderr io.Reader) ([]string, error) {
+	scanner := bufio.NewScanner(stderr)
+
+	instantiated := make([]string, 0, instantiatedInitialCap)
+	for scanner.Scan() {
+		// on error, process is killed by deferred context cancel
+
+		if len(instantiated) == cap(instantiated) {
+			// grow the buffer exponentially to minimise copies
+			instantiated = slices.Grow(instantiated, cap(instantiated)<<1)
+		}
+
+		v := scanner.Text()
+		if !strings.HasPrefix(v, instantiatedPrefix) {
+			continue
+		}
+		f := strings.SplitN(v, instantiatedSeparator, instantiatedFields)
+		if len(f) != instantiatedFields {
+			return nil, &MalformedInstantiatedError{v, InstantiatedBadFields}
+		}
+
+		// very basic validation here: the output format is not fully understood
+		if len(f[1]) < 3 || f[1][0] != '\'' || f[1][len(f[1])-1] != '\'' {
+			return nil, &MalformedInstantiatedError{v, InstantiatedUnexpectedQuotes}
+		}
+		drv := f[1][1 : len(f[1])-1]
+
+		if !path.IsAbs(drv) {
+			return nil, &MalformedInstantiatedError{v, InstantiatedNotAbsolute}
+		}
+
+		instantiated = append(instantiated, drv)
+	}
+
+	slices.Sort(instantiated)
+	return slices.Compact(instantiated), scanner.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
+// 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)
+	defer cancel()
+
+	cmd := exec.CommandContext(c,
+		"nix", "build", installable,
+		// 'instantiated' messages  are only emitted when actually evaluating something
+		"--option", "eval-cache", "false",
+		// do not actually build anything
+		"--dry-run",
+		// increase verbosity so nix outputs 'instantiated' messages
+		"-Lvvv",
+	)
+
+	stderr, err := cmd.StderrPipe()
+	if err != nil {
+		return nil, err
+	}
+
+	if err := cmd.Start(); err != nil {
+		// have finalizer take care of the pipe
+		return nil, err
+	}
+
+	instantiated, decodeErr := DecodeInstantiated(stderr)
+	waitErr := cmd.Wait()
+	return instantiated, errors.Join(decodeErr, waitErr)
+}

instantiated_test.go

@@ -0,0 +1,121 @@
+package nixbuild_test
+
+import (
+	"errors"
+	"runtime"
+	"slices"
+	"strings"
+	"testing"
+
+	"git.gensokyo.uk/yonah/nixbuild"
+)
+
+func TestDecodeInstantiated(t *testing.T) {
+	testCases := []struct {
+		name    string
+		out     string
+		want    []string
+		wantErr error
+	}{
+		{"bad fields", segmentPrefix + `instantiated 'config.sub-948ae97' ` + segmentSuffix, nil,
+			&nixbuild.MalformedInstantiatedError{Type: nixbuild.InstantiatedBadFields}},
+		{"unexpected quotes left", segmentPrefix + `instantiated 'config.sub-948ae97' -> /n'` + segmentSuffix, nil,
+			&nixbuild.MalformedInstantiatedError{Type: nixbuild.InstantiatedUnexpectedQuotes}},
+		{"unexpected quotes right", segmentPrefix + `instantiated 'config.sub-948ae97' -> '/n` + segmentSuffix, nil,
+			&nixbuild.MalformedInstantiatedError{Type: nixbuild.InstantiatedUnexpectedQuotes}},
+		{"unexpected quotes short", segmentPrefix + `instantiated 'config.sub-948ae97' -> ''` + segmentSuffix, nil,
+			&nixbuild.MalformedInstantiatedError{Type: nixbuild.InstantiatedUnexpectedQuotes}},
+		{"not absolute", segmentPrefix + `instantiated 'config.sub-948ae97' -> ' '` + segmentSuffix, nil,
+			&nixbuild.MalformedInstantiatedError{Type: nixbuild.InstantiatedNotAbsolute}},
+		{"good segment", segmentPrefix + segmentBody + segmentSuffix, []string{
+			"/nix/store/3zilrlmq7r6rpzfd94mwss32b62yinj5-bootstrap-stage0-stdenv-linux.drv",
+			"/nix/store/7yfwy95p6lcdpljdajs5aw10h6q0sfx0-update-autotools-gnu-config-scripts-hook.drv",
+			"/nix/store/bamwxswxacs3cjdcydv0z7bj22d7g2kc-config.guess-948ae97.drv",
+			"/nix/store/gyks6vvl7x0gq214ldjhi3w4rg37nh8i-zlib-1.3.1.tar.gz.drv",
+			"/nix/store/nbsdqpfzh1jlpmh95s69b3iivfcvv3lh-config.sub-948ae97.drv",
+			"/nix/store/ysp83x9nrks28zkblqmnc1s1kb68dr69-gnu-config-2024-01-01.drv",
+		}, nil},
+
+		{"getchoo atlas", getchooAtlasOut, getchooAtlas, nil},
+		{"getchoo glados", getchooGladosOut, getchooGlados, nil},
+		{"pluiedev pappardelle", pluiedevPappardelleOut, pluiedevPappardelle, nil},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			stderr := strings.NewReader(tc.out)
+			got, err := nixbuild.DecodeInstantiated(stderr)
+			if !errors.Is(err, tc.wantErr) {
+				t.Fatalf("DecodeInstantiated: error = %v, want %v", err, tc.wantErr)
+			}
+			if tc.wantErr != nil {
+				t.Logf("DecodeInstantiated: error = %v", err)
+				return
+			}
+			if !slices.Equal(got, tc.want) {
+				t.Errorf("DecodeInstantiated: %#v, want %#v", got, tc.want)
+			}
+		})
+	}
+
+	t.Run("errors", func(t *testing.T) {
+		t.Run("bad type", func(t *testing.T) {
+			badErr := errors.New("")
+			if errors.Is(new(nixbuild.MalformedInstantiatedError), badErr) {
+				t.Error("unexpected MalformedInstantiatedError equivalence")
+			}
+		})
+
+		t.Run("nil", func(t *testing.T) {
+			if errors.Is(new(nixbuild.MalformedInstantiatedError), (*nixbuild.MalformedInstantiatedError)(nil)) {
+				t.Error("unexpected MalformedInstantiatedError equivalence")
+			}
+		})
+	})
+}
+
+const (
+	segmentPrefix = `evaluating file '/nix/store/vdzlppvrdkz9rv14q4j02g9kpjbww2ww-source/pkgs/development/libraries/zlib/default.nix'
+evaluating file '/nix/store/vdzlppvrdkz9rv14q4j02g9kpjbww2ww-source/pkgs/build-support/fetchurl/boot.nix'
+performing daemon worker op: 7
+instantiated 'zlib-1.3.1.tar.gz' -> '/nix/store/gyks6vvl7x0gq214ldjhi3w4rg37nh8i-zlib-1.3.1.tar.gz.drv'
+source path '/nix/store/vdzlppvrdkz9rv14q4j02g9kpjbww2ww-source/pkgs/build-support/setup-hooks/update-autotools-gnu-config-scripts.sh' is uncacheable
+copying '/nix/store/vdzlppvrdkz9rv14q4j02g9kpjbww2ww-source/pkgs/build-support/setup-hooks/update-autotools-gnu-config-scripts.sh' to the store...
+performing daemon worker op: 7
+copied '/nix/store/vdzlppvrdkz9rv14q4j02g9kpjbww2ww-source/pkgs/build-support/setup-hooks/update-autotools-gnu-config-scripts.sh' to '/nix/store/96rvfw5vlv1hwwm9sdxhdkkpjyym6p2x-update-autotools-gnu-config-scripts.sh'
+copied source '/nix/store/vdzlppvrdkz9rv14q4j02g9kpjbww2ww-source/pkgs/build-support/setup-hooks/update-autotools-gnu-config-scripts.sh' -> '/nix/store/96rvfw5vlv1hwwm9sdxhdkkpjyym6p2x-update-autotools-gnu-config-scripts.sh'
+evaluating file '/nix/store/vdzlppvrdkz9rv14q4j02g9kpjbww2ww-source/pkgs/by-name/gn/gnu-config/package.nix'
+performing daemon worker op: 7
+instantiated 'config.guess-948ae97' -> '/nix/store/bamwxswxacs3cjdcydv0z7bj22d7g2kc-config.guess-948ae97.drv'
+performing daemon worker op: 7
+`
+
+	segmentBody = `instantiated 'config.sub-948ae97' -> '/nix/store/nbsdqpfzh1jlpmh95s69b3iivfcvv3lh-config.sub-948ae97.drv'`
+
+	segmentSuffix = `
+performing daemon worker op: 7
+instantiated 'gnu-config-2024-01-01' -> '/nix/store/ysp83x9nrks28zkblqmnc1s1kb68dr69-gnu-config-2024-01-01.drv'
+performing daemon worker op: 7
+instantiated 'bootstrap-stage0-stdenv-linux' -> '/nix/store/3zilrlmq7r6rpzfd94mwss32b62yinj5-bootstrap-stage0-stdenv-linux.drv'
+performing daemon worker op: 7
+instantiated 'update-autotools-gnu-config-scripts-hook' -> '/nix/store/7yfwy95p6lcdpljdajs5aw10h6q0sfx0-update-autotools-gnu-config-scripts-hook.drv'
+source path '/nix/store/vdzlppvrdkz9rv14q4j02g9kpjbww2ww-source/pkgs/build-support/bintools-wrapper/ld-wrapper.sh' is uncacheable
+copying '/nix/store/vdzlppvrdkz9rv14q4j02g9kpjbww2ww-source/pkgs/build-support/bintools-wrapper/ld-wrapper.sh' to the store...`
+)
+
+func BenchmarkDecodeInstantiated(b *testing.B) {
+	stderr := strings.NewReader(pluiedevPappardelleOut)
+	var v []string
+	for i := 0; i < b.N; i++ {
+		v, _ = nixbuild.DecodeInstantiated(stderr)
+		runtime.KeepAlive(v)
+	}
+}
+
+func BenchmarkDecodeInstantiatedCopy(b *testing.B) {
+	stderr := strings.NewReader(getchooAtlasOut)
+	var v []string
+	for i := 0; i < b.N; i++ {
+		v, _ = nixbuild.DecodeInstantiated(stderr)
+		runtime.KeepAlive(v)
+	}
+}