internal/pkg: record cache variant on-disk

This makes custom artifacts much less error-prone to use.

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

internal/pkg/pkg_test.go

@@ -41,6 +41,25 @@ func unsafeOpen(
 	lock bool,
 ) (*pkg.Cache, error)
 
+var (
+	// extension is a string uniquely identifying a set of custom [Artifact]
+	// implementations registered by calling [Register].
+	//
+	//go:linkname extension hakurei.app/internal/pkg.extension
+	extension string
+
+	// opened is false if [Open] was never called.
+	//
+	//go:linkname opened hakurei.app/internal/pkg.opened
+	opened bool
+
+	// irArtifact refers to artifact IR interpretation functions and must not be
+	// written to directly.
+	//
+	//go:linkname irArtifact hakurei.app/internal/pkg.irArtifact
+	irArtifact map[pkg.Kind]pkg.IRReadFunc
+)
+
 // newRContext returns the address of a new [pkg.RContext] unsafely created for
 // the specified [testing.TB].
 func newRContext(tb testing.TB, c *pkg.Cache) *pkg.RContext {
@@ -342,9 +361,20 @@ func checkWithCache(t *testing.T, testCases []cacheTestCase) {
 				restoreTemp = true
 			}
 
-			// destroy lock file to avoid changing cache checksums
-			if err := os.Remove(base.Append("lock").String()); err != nil {
-				t.Fatal(err)
+			// destroy lock and variant file to avoid changing cache checksums
+			for _, s := range []string{
+				"lock",
+				"variant",
+			} {
+				pathname := base.Append(s)
+				if p, err := os.ReadFile(pathname.String()); err != nil {
+					t.Fatal(err)
+				} else if len(p) != 0 {
+					t.Fatalf("file %q: %q", s, string(p))
+				}
+				if err := os.Remove(pathname.String()); err != nil {
+					t.Fatal(err)
+				}
 			}
 
 			// destroy non-deterministic status files
@@ -1101,6 +1131,10 @@ func TestErrors(t *testing.T) {
 			Want:      pkg.IRKindIdent,
 			Ancillary: 0xcafe,
 		}, "got invalid kind 48879 IR value (0xcafe) instead of ident"},
+
+		{"UnsupportedVariantError", pkg.UnsupportedVariantError(
+			"rosa",
+		), `unsupported variant "rosa"`},
 	}
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
@@ -1309,6 +1343,8 @@ func (a earlyFailureF) Cure(*pkg.FContext) error {
 }
 
 func TestDependencyCureErrorEarly(t *testing.T) {
+	t.Parallel()
+
 	checkWithCache(t, []cacheTestCase{
 		{"early", 0, nil, func(t *testing.T, _ *check.Absolute, c *pkg.Cache) {
 			_, _, err := c.Cure(earlyFailureF(8))
@@ -1319,7 +1355,7 @@ func TestDependencyCureErrorEarly(t *testing.T) {
 	})
 }
 
-func TestNew(t *testing.T) {
+func TestOpen(t *testing.T) {
 	t.Parallel()
 
 	t.Run("nonexistent", func(t *testing.T) {
@@ -1367,3 +1403,219 @@ func TestNew(t *testing.T) {
 		}
 	})
 }
+
+func TestExtensionRegister(t *testing.T) {
+	extensionOld := extension
+	openedOld := opened
+	t.Cleanup(func() { extension = extensionOld; opened = openedOld })
+	extension = ""
+	opened = false
+
+	t.Run("set", func(t *testing.T) {
+		t.Cleanup(func() { extension = "" })
+
+		const want = "rosa"
+		pkg.SetExtension(want)
+		if got := pkg.Extension(); got != want {
+			t.Fatalf("Extension: %q, want %q", got, want)
+		}
+	})
+
+	t.Run("twice", func(t *testing.T) {
+		t.Cleanup(func() { extension = "" })
+
+		defer func() {
+			const wantPanic = "attempting to set extension twice"
+			if r := recover(); r != wantPanic {
+				t.Errorf("panic: %#v, want %q", r, wantPanic)
+			}
+		}()
+		pkg.SetExtension("rosa")
+		pkg.SetExtension("rosa")
+	})
+
+	t.Run("invalid", func(t *testing.T) {
+		defer func() {
+			var wantPanic = pkg.ErrInvalidExtension
+			if r := recover(); r != wantPanic {
+				t.Errorf("panic: %#v, want %#v", r, wantPanic)
+			}
+		}()
+		pkg.SetExtension(" ")
+	})
+
+	t.Run("opened", func(t *testing.T) {
+		t.Cleanup(func() { opened = false })
+
+		if _, err := pkg.Open(
+			t.Context(),
+			message.New(log.Default()),
+			0, 0, 0,
+			check.MustAbs(container.Nonexistent),
+		); !errors.Is(err, os.ErrNotExist) {
+			t.Fatalf("Open: error = %v", err)
+		}
+
+		t.Run("variant", func(t *testing.T) {
+			defer func() {
+				const wantPanic = "attempting to set extension after open"
+				if r := recover(); r != wantPanic {
+					t.Errorf("panic: %#v, want %q", r, wantPanic)
+				}
+			}()
+			pkg.SetExtension("rosa")
+		})
+
+		t.Run("register", func(t *testing.T) {
+			defer func() {
+				const wantPanic = "attempting to register after open"
+				if r := recover(); r != wantPanic {
+					t.Errorf("panic: %#v, want %q", r, wantPanic)
+				}
+			}()
+			pkg.Register(pkg.KindCustomOffset, nil)
+		})
+	})
+
+	t.Run("incomplete", func(t *testing.T) {
+		t.Cleanup(func() { delete(irArtifact, pkg.KindCustomOffset) })
+
+		defer func() {
+			const wantPanic = "attempting to open cache with incomplete variant setup"
+			if r := recover(); r != wantPanic {
+				t.Errorf("panic: %#v, want %q", r, wantPanic)
+			}
+		}()
+		pkg.Register(pkg.KindCustomOffset, nil)
+
+		t.Cleanup(func() { opened = false })
+		_, _ = pkg.Open(nil, nil, 0, 0, 0, nil)
+		panic("unreachable")
+	})
+
+	t.Run("create", func(t *testing.T) {
+		t.Cleanup(func() { extension = "" })
+		const want = "rosa"
+		pkg.SetExtension(want)
+
+		base := check.MustAbs(t.TempDir())
+		t.Cleanup(func() { opened = false })
+		if c, err := pkg.Open(
+			t.Context(), nil,
+			0, 0, 0,
+			base,
+		); err != nil {
+			t.Fatal(err)
+		} else {
+			c.Close()
+		}
+
+		if got, err := os.ReadFile(base.Append("variant").String()); err != nil {
+			t.Fatal(err)
+		} else if string(got) != want {
+			t.Fatalf("variant: %q", string(got))
+		}
+	})
+
+	t.Run("access", func(t *testing.T) {
+		base := check.MustAbs(t.TempDir())
+		t.Cleanup(func() { opened = false })
+
+		if err := os.WriteFile(base.Append("variant").String(), nil, 0); err != nil {
+			t.Fatal(err)
+		}
+
+		wantErr := &os.PathError{
+			Op:   "open",
+			Path: base.Append("variant").String(),
+			Err:  syscall.EACCES,
+		}
+		if _, err := pkg.Open(
+			t.Context(), nil,
+			0, 0, 0,
+			base,
+		); !reflect.DeepEqual(err, wantErr) {
+			t.Fatalf("Open: error = %v, want %v", err, wantErr)
+		}
+	})
+
+	t.Run("promote", func(t *testing.T) {
+		t.Cleanup(func() { extension = "" })
+		const want = "rosa"
+		pkg.SetExtension(want)
+
+		base := check.MustAbs(t.TempDir())
+		t.Cleanup(func() { opened = false })
+
+		variantPath := base.Append("variant")
+		if err := os.WriteFile(variantPath.String(), nil, 0600); err != nil {
+			t.Fatal(err)
+		}
+
+		if _, err := pkg.Open(
+			t.Context(), nil,
+			0, 0, 0,
+			base,
+		); !reflect.DeepEqual(err, pkg.ErrWouldPromote) {
+			t.Fatalf("Open: error = %v", err)
+		}
+
+		if p, err := os.ReadFile(variantPath.String()); err != nil {
+			t.Fatal(err)
+		} else if len(p) != 0 {
+			t.Fatalf("variant: %q", string(p))
+		}
+
+		if c, err := pkg.Open(
+			t.Context(), nil,
+			pkg.CPromoteVariant, 0, 0,
+			base,
+		); err != nil {
+			t.Fatalf("Open: error = %v", err)
+		} else {
+			c.Close()
+		}
+
+		if p, err := os.ReadFile(variantPath.String()); err != nil {
+			t.Fatal(err)
+		} else if string(p) != want {
+			t.Fatalf("variant: %q, want %q", string(p), want)
+		}
+	})
+
+	t.Run("open invalid", func(t *testing.T) {
+		base := check.MustAbs(t.TempDir())
+		t.Cleanup(func() { opened = false })
+
+		variantPath := base.Append("variant")
+		if err := os.WriteFile(variantPath.String(), make([]byte, 129), 0400); err != nil {
+			t.Fatal(err)
+		}
+
+		if _, err := pkg.Open(
+			t.Context(), nil,
+			0, 0, 0,
+			base,
+		); !reflect.DeepEqual(err, pkg.ErrInvalidExtension) {
+			t.Fatalf("Open: error = %v", err)
+		}
+	})
+
+	t.Run("unsupported", func(t *testing.T) {
+		base := check.MustAbs(t.TempDir())
+		t.Cleanup(func() { opened = false })
+
+		variantPath := base.Append("variant")
+		if err := os.WriteFile(variantPath.String(), []byte("rosa"), 0400); err != nil {
+			t.Fatal(err)
+		}
+
+		if _, err := pkg.Open(
+			t.Context(), nil,
+			0, 0, 0,
+			base,
+		); !reflect.DeepEqual(err, pkg.UnsupportedVariantError("rosa")) {
+			t.Fatalf("Open: error = %v", err)
+		}
+	})
+}