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extern.go
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extern.go
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// Copyright 2023 CUE 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 runtime
import (
"cuelang.org/go/cue/ast"
"cuelang.org/go/cue/build"
"cuelang.org/go/cue/errors"
"cuelang.org/go/cue/format"
"cuelang.org/go/cue/token"
"cuelang.org/go/internal"
"cuelang.org/go/internal/core/adt"
"cuelang.org/go/internal/core/walk"
)
// SetInterpreter sets the interpreter for interpretation of files marked with
// @extern(kind).
func (r *Runtime) SetInterpreter(i Interpreter) {
if r.interpreters == nil {
r.interpreters = map[string]Interpreter{}
}
r.interpreters[i.Kind()] = i
}
// TODO: consider also passing the top-level attribute to NewCompiler to allow
// passing default values.
// Interpreter defines an entrypoint for creating per-package interpreters.
type Interpreter interface {
// NewCompiler creates a compiler for b and reports any errors.
NewCompiler(b *build.Instance) (Compiler, errors.Error)
// Kind returns the string to be used in the file-level @extern attribute.
Kind() string
}
// A Compiler composes an adt.Builtin for an external function implementation.
type Compiler interface {
// Compile creates a builtin for the given function name and attribute.
// funcName is the name of the function to compile, taken from altName in
// @extern(name=altName), or from the field name if that's not defined.
// Other than "name", the fields in a are implementation specific.
Compile(funcName string, a *internal.Attr) (*adt.Builtin, errors.Error)
}
// injectImplementations modifies v to include implementations of functions
// for fields associated with the @extern attributes.
func (r *Runtime) injectImplementations(b *build.Instance, v *adt.Vertex) (errs errors.Error) {
if r.interpreters == nil {
return nil
}
d := &externDecorator{
runtime: r,
pkg: b,
}
for _, f := range b.Files {
d.errs = errors.Append(d.errs, d.addFile(f))
}
for _, c := range v.Conjuncts {
d.decorateConjunct(c.Elem())
}
return d.errs
}
// externDecorator locates extern attributes and calls the relevant interpreters
// to inject builtins.
//
// This is a two-pass algorithm: in the first pass, all ast.Files are processed
// to build an index from *ast.Fields to attributes. In the second phase, the
// corresponding adt.Fields are located in the ADT and decorated with the
// builtins.
type externDecorator struct {
runtime *Runtime
pkg *build.Instance
compilers map[string]Compiler
fields map[*ast.Field]fieldInfo
errs errors.Error
}
type fieldInfo struct {
file *ast.File
extern string
funcName string
attrBody string
attr *ast.Attribute
}
// addFile finds injection points in the given ast.File for external
// implementations of Builtins.
func (d *externDecorator) addFile(f *ast.File) (errs errors.Error) {
kind, pos, decls, err := findExternFileAttr(f)
if len(decls) == 0 {
return err
}
ok, err := d.initCompiler(kind, pos)
if !ok {
return err
}
return d.markExternFieldAttr(kind, decls)
}
// findExternFileAttr reports the extern kind of a file-level @extern(kind)
// attribute in f, the position of the corresponding attribute, and f's
// declarations from the package directive onwards. It's an error if more than
// one @extern attribute is found. decls == nil signals that this file should be
// skipped.
func findExternFileAttr(f *ast.File) (kind string, pos token.Pos, decls []ast.Decl, err errors.Error) {
var (
hasPkg bool
p int
fileAttr *ast.Attribute
)
loop:
for ; p < len(f.Decls); p++ {
switch a := f.Decls[p].(type) {
case *ast.Package:
hasPkg = true
break loop
case *ast.Attribute:
pos = a.Pos()
key, body := a.Split()
if key != "extern" {
continue
}
fileAttr = a
attr := internal.ParseAttrBody(a.Pos(), body)
if attr.Err != nil {
return "", pos, nil, attr.Err
}
k, err := attr.String(0)
if err != nil {
// Unreachable.
return "", pos, nil, errors.Newf(a.Pos(), "%s", err)
}
if k == "" {
return "", pos, nil, errors.Newf(a.Pos(),
"interpreter name must be non-empty")
}
if kind != "" {
return "", pos, nil, errors.Newf(a.Pos(),
"only one file-level extern attribute allowed per file")
}
kind = k
}
}
switch {
case fileAttr == nil && !hasPkg:
// Nothing to see here.
return "", pos, nil, nil
case fileAttr != nil && !hasPkg:
return "", pos, nil, errors.Newf(fileAttr.Pos(),
"extern attribute without package clause")
case fileAttr == nil && hasPkg:
// Check that there are no top-level extern attributes.
for p++; p < len(f.Decls); p++ {
x, ok := f.Decls[p].(*ast.Attribute)
if !ok {
continue
}
if key, _ := x.Split(); key == "extern" {
err = errors.Append(err, errors.Newf(x.Pos(),
"extern attribute must appear before package clause"))
}
}
return "", pos, nil, err
}
return kind, pos, f.Decls[p:], nil
}
// initCompiler initializes the runtime for kind, if applicable. The pos
// argument represents the position of the file-level @extern attribute.
func (d *externDecorator) initCompiler(kind string, pos token.Pos) (ok bool, err errors.Error) {
if c, ok := d.compilers[kind]; ok {
return c != nil, nil
}
// initialize the compiler.
if d.compilers == nil {
d.compilers = map[string]Compiler{}
d.fields = map[*ast.Field]fieldInfo{}
}
x := d.runtime.interpreters[kind]
if x == nil {
return false, errors.Newf(pos, "no interpreter defined for %q", kind)
}
c, err := x.NewCompiler(d.pkg)
if err != nil {
return false, err
}
d.compilers[kind] = c
return c != nil, nil
}
// markExternFieldAttr collects all *ast.Fields with extern attributes into
// d.fields. Both of the following forms are allowed:
//
// a: _ @extern(...)
// a: { _, @extern(...) }
//
// consistent with attribute implementation recommendations.
func (d *externDecorator) markExternFieldAttr(kind string, decls []ast.Decl) (errs errors.Error) {
var fieldStack []*ast.Field
ast.Walk(&ast.File{Decls: decls}, func(n ast.Node) bool {
switch x := n.(type) {
case *ast.Field:
fieldStack = append(fieldStack, x)
case *ast.Attribute:
key, body := x.Split()
if key != "extern" {
break
}
lastField := len(fieldStack) - 1
if lastField < 0 {
errs = errors.Append(errs, errors.Newf(x.Pos(),
"extern attribute not associated with field"))
return true
}
f := fieldStack[lastField]
if _, ok := d.fields[f]; ok {
errs = errors.Append(errs, errors.Newf(x.Pos(),
"duplicate extern attributes"))
return true
}
name, isIdent, err := ast.LabelName(f.Label)
if err != nil || !isIdent {
b, _ := format.Node(f.Label)
errs = errors.Append(errs, errors.Newf(x.Pos(),
"can only define functions for fields with identifier names, found %v", string(b)))
return true
}
d.fields[f] = fieldInfo{
extern: kind,
funcName: name,
attrBody: body,
attr: x,
}
}
return true
}, func(n ast.Node) {
switch n.(type) {
case *ast.Field:
fieldStack = fieldStack[:len(fieldStack)-1]
}
})
return errs
}
func (d *externDecorator) decorateConjunct(e adt.Elem) {
w := walk.Visitor{Before: d.processADTNode}
w.Elem(e)
}
// processADTNode injects a builtin conjunct into n if n is an adt.Field and
// has a marked ast.Field associated with it.
func (d *externDecorator) processADTNode(n adt.Node) bool {
f, ok := n.(*adt.Field)
if !ok {
return true
}
info, ok := d.fields[f.Src]
if !ok {
return true
}
c, ok := d.compilers[info.extern]
if !ok {
// An error for a missing runtime was already reported earlier,
// if applicable.
return true
}
attr := internal.ParseAttrBody(info.attr.Pos(), info.attrBody)
if attr.Err != nil {
d.errs = errors.Append(d.errs, attr.Err)
return true
}
name := info.funcName
if str, ok, _ := attr.Lookup(1, "name"); ok {
name = str
}
b, err := c.Compile(name, &attr)
if err != nil {
err = errors.Newf(info.attr.Pos(), "can't load from external module: %v", err)
d.errs = errors.Append(d.errs, err)
return true
}
f.Value = &adt.BinaryExpr{
Op: adt.AndOp,
X: f.Value,
Y: b,
}
return true
}