| // Copyright 2023 The Shac Authors |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| package engine |
| |
| import ( |
| "context" |
| "errors" |
| "fmt" |
| "io" |
| "io/fs" |
| "path" |
| "strings" |
| "sync" |
| |
| "go.starlark.net/resolve" |
| "go.starlark.net/starlark" |
| "go.starlark.net/syntax" |
| ) |
| |
| type printImpl func(th *starlark.Thread, msg string) |
| |
| // sourceKey is a reference as parsed by load(). |
| type sourceKey struct { |
| orig string |
| pkg string |
| relpath string |
| } |
| |
| func (s *sourceKey) String() string { |
| if s.pkg == "__main__" { |
| return "//" + s.relpath |
| } |
| return "@" + s.pkg + "//" + s.relpath |
| } |
| |
| func parseSourceKey(parent sourceKey, s string) (sourceKey, error) { |
| sk := sourceKey{orig: s} |
| if s == "" { |
| return sk, errors.New("empty reference") |
| } |
| // It is an external reference. |
| if strings.HasPrefix(s, "@") { |
| parts := strings.SplitN(s[1:], "//", 2) |
| sk.pkg = parts[0] |
| if len(parts) == 1 { |
| // The root of a package is api.star, to not conflict with self-tests that |
| // would live in shac.star. |
| if strings.HasSuffix(sk.pkg, "/") { |
| return sk, fmt.Errorf("illegal external reference trailing \"/\": %s", s) |
| } |
| sk.relpath = "api.star" |
| } else { |
| // A file within the package is referenced. |
| if len(parts[1]) == 0 { |
| return sk, fmt.Errorf("illegal external reference path empty: %s", s) |
| } |
| for _, p := range strings.SplitN(parts[1], "/", -1) { |
| if p == "internal" { |
| return sk, fmt.Errorf("illegal external reference path containing \"internal\": %s", s) |
| } |
| if p == ".." { |
| return sk, fmt.Errorf("illegal external reference path containing \"..\": %s", s) |
| } |
| if p == "" { |
| return sk, fmt.Errorf("illegal external reference path containing \"//\": %s", s) |
| } |
| } |
| sk.relpath = parts[1] |
| } |
| return sk, nil |
| } |
| |
| // It is an internal reference. |
| sk.pkg = parent.pkg |
| if strings.HasPrefix(s, "//") { |
| // It is root relative. |
| sk.relpath = s[2:] |
| } else { |
| // It is path relative. |
| sk.relpath = path.Clean(path.Join(path.Dir(parent.relpath), s)) |
| } |
| return sk, nil |
| } |
| |
| // loadedSource is the outcome of a load() statement. |
| type loadedSource struct { |
| // th is the starlark thread that loaded this source file. |
| th *starlark.Thread |
| |
| mu sync.Mutex |
| globals starlark.StringDict |
| err error |
| } |
| |
| // starlarkEnv is the running environment enabling to run multiple starlark |
| // files in parallel. |
| type starlarkEnv struct { |
| // Immutable. |
| // execedFileGlobals is available to the top-level Starlark file. They must be frozen |
| // via Freeze(). |
| execedFileGlobals starlark.StringDict |
| // loadedFileGlobals is available to any loaded Starlark files. They must be |
| // frozen via Freeze(). |
| loadedFileGlobals starlark.StringDict |
| // packages are all the available packages. It must include __main__. |
| packages map[string]fs.FS |
| |
| // Mutable. |
| mu sync.Mutex |
| // sources are the processed sources. Augments as more sources are added. |
| sources map[string]*loadedSource |
| } |
| |
| // thread returns a new starlark thread. |
| // |
| // load() statement is not allowed. |
| func (s *starlarkEnv) thread(ctx context.Context, name string, pi printImpl) *starlark.Thread { |
| t := &starlark.Thread{Name: name, Print: pi} |
| t.SetLocal("shac.context", ctx) |
| return t |
| } |
| |
| // getContext returns the context.Context given a starlark thread. |
| func getContext(t *starlark.Thread) context.Context { |
| return t.Local("shac.context").(context.Context) |
| } |
| |
| // load loads a starlark source file. It is safe to call it concurrently. |
| // |
| // A thread will be implicitly created. |
| func (s *starlarkEnv) load(ctx context.Context, sk sourceKey, pi printImpl) (starlark.StringDict, error) { |
| // We are the root thread. Start a thread implicitly. |
| t := s.thread(ctx, sk.String(), pi) |
| t.Load = func(th *starlark.Thread, str string) (starlark.StringDict, error) { |
| skn, err := parseSourceKey(th.Local("shac.pkg").(sourceKey), str) |
| if err != nil { |
| return nil, err |
| } |
| return s.loadInner(ctx, th, skn, pi, false) |
| } |
| t.SetLocal("shac.top", sk) |
| t.SetLocal("shac.pkg", sk) |
| return s.loadInner(ctx, t, sk, pi, true) |
| } |
| |
| func (s *starlarkEnv) loadInner(ctx context.Context, th *starlark.Thread, sk sourceKey, pi printImpl, execed bool) (starlark.StringDict, error) { |
| key := sk.String() |
| s.mu.Lock() |
| ss, ok := s.sources[key] |
| if !ok { |
| ss = &loadedSource{th: th, err: fmt.Errorf("load(%q) failed: panic while loading", sk)} |
| // We are the "master" of this file, since we will be loading it. Make sure |
| // others won't load it. |
| ss.mu.Lock() |
| s.sources[key] = ss |
| // It's a new file that wasn't load'ed yet. ss.mu is still held which will |
| // block concurrent loading. |
| defer ss.mu.Unlock() |
| } |
| s.mu.Unlock() |
| |
| if ok { |
| if ss.th == th { |
| // This source was loaded by this very thread. |
| return nil, fmt.Errorf("%s was loaded in a cycle dependency graph", sk.String()) |
| } |
| // These lines are hard to cover since it's a race condition. We'd have to |
| // inject a builtin that would hang the starlark execution to force |
| // concurrency. |
| // The source may be concurrently processed by another starlark thread, |
| // wait for the processing to complete by taking the lock. |
| ss.mu.Lock() |
| g := ss.globals |
| err := ss.err |
| ss.mu.Unlock() |
| return g, err |
| } |
| |
| // It's a new file that wasn't load'ed yet. ss.mu is still held which will |
| // block concurrent loading. |
| if pkg := s.packages[sk.pkg]; pkg != nil { |
| if f, err := pkg.Open(sk.relpath); err == nil { |
| var d []byte |
| if d, err = io.ReadAll(f); err == nil { |
| oldsk := th.Local("shac.pkg").(sourceKey) |
| th.SetLocal("shac.pkg", sk) |
| fp := syntax.FilePortion{Content: d, FirstLine: 1, FirstCol: 1} |
| globals := s.execedFileGlobals |
| if !execed { |
| globals = s.loadedFileGlobals |
| } |
| ss.globals, ss.err = starlark.ExecFile(th, sk.String(), fp, globals) |
| th.SetLocal("shac.pkg", oldsk) |
| var errl resolve.ErrorList |
| if errors.As(ss.err, &errl) { |
| // Unwrap the error, only keep the first one. |
| ss.err = errl[0] |
| } |
| var errre resolve.Error |
| if errors.As(ss.err, &errre) { |
| // Synthesize a BacktracableError since it's nicer for the user. |
| // Sadly we can't get the function context even if the error is |
| // within a function implementation, so hardcode "<toplevel>". |
| ss.err = &failure{ |
| Message: errre.Msg, |
| Stack: starlark.CallStack{ |
| starlark.CallFrame{ |
| Name: "<toplevel>", |
| Pos: errre.Pos, |
| }, |
| }, |
| } |
| } |
| } else { |
| ss.err = err |
| } |
| if err = f.Close(); ss.err == nil { |
| ss.err = err |
| } |
| } else if errors.Is(err, fs.ErrNotExist) { |
| // Hide the underlying error for determinism. |
| ss.err = errors.New("file not found") |
| } else { |
| ss.err = err |
| } |
| } else { |
| ss.err = errors.New("package not found") |
| } |
| return ss.globals, ss.err |
| } |