internal/core/dep: first stab at precise dependency analyzer

Change-Id: I0bf5de9a1b2421ddffa4108c6dbffd38dae2cfe0
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/7604
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

internal/core/adt/context.go

@@ -340,6 +340,14 @@ func (c *OpContext) Resolve(env *Environment, r Resolver) (*Vertex, *Bottom) {
 		return nil, arc.ChildErrors
 	}
 
+	for {
+		x, ok := arc.Value.(*Vertex)
+		if !ok {
+			break
+		}
+		arc = x
+	}
+
 	return arc, err
 }
 

internal/core/dep/dep.go

@@ -0,0 +1,311 @@
+// Copyright 2020 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 dep analyzes dependencies between values.
+package dep
+
+import (
+	"errors"
+
+	"cuelang.org/go/internal/core/adt"
+)
+
+// A Dependency is a reference and the node that reference resolves to.
+type Dependency struct {
+	// Node is the referenced node.
+	Node *adt.Vertex
+
+	// Reference is the expression that referenced the node.
+	Reference adt.Resolver
+
+	top bool
+}
+
+// Import returns the import reference or nil if the reference was within
+// the same package as the visited Vertex.
+func (d *Dependency) Import() *adt.ImportReference {
+	x, _ := d.Reference.(adt.Expr)
+	return importRef(x)
+}
+
+// IsRoot reports whether the dependency is referenced by the root of the
+// original Vertex passed to any of the Visit* functions, and not one of its
+// descendent arcs. This always returns true for Visit().
+func (d *Dependency) IsRoot() bool {
+	return d.top
+}
+
+func (d *Dependency) Path() []adt.Feature {
+	return nil
+}
+
+func importRef(r adt.Expr) *adt.ImportReference {
+	switch x := r.(type) {
+	case *adt.ImportReference:
+		return x
+	case *adt.SelectorExpr:
+		return importRef(x.X)
+	case *adt.IndexExpr:
+		return importRef(x.X)
+	}
+	return nil
+}
+
+// VisitFunc is used for reporting dependencies.
+type VisitFunc func(Dependency) error
+
+// Visit calls f for all vertices referenced by the conjuncts of n without
+// descending into the elements of list or fields of structs. Only references
+// that do not refer to the conjuncts of n itself are reported.
+func Visit(c *adt.OpContext, n *adt.Vertex, f VisitFunc) error {
+	return visit(c, n, f, false, true)
+}
+
+// VisitAll calls f for all vertices referenced by the conjuncts of n including
+// those of descendant fields and elements. Only references that do not refer to
+// the conjuncts of n itself are reported.
+func VisitAll(c *adt.OpContext, n *adt.Vertex, f VisitFunc) error {
+	return visit(c, n, f, true, true)
+}
+
+var empty *adt.Vertex
+
+func init() {
+	empty = &adt.Vertex{}
+	empty.UpdateStatus(adt.Finalized)
+}
+
+func visit(c *adt.OpContext, n *adt.Vertex, f VisitFunc, all, top bool) (err error) {
+	if c == nil {
+		panic("nil context")
+	}
+	v := visitor{
+		ctxt:  c,
+		visit: f,
+		node:  n,
+		all:   all,
+		top:   top,
+	}
+
+	defer func() {
+		switch x := recover(); x {
+		case nil:
+		case aborted:
+			err = v.err
+		default:
+			panic(x)
+		}
+	}()
+
+	for _, x := range n.Conjuncts {
+		v.markExpr(x.Env, x.Expr())
+	}
+
+	return nil
+}
+
+var aborted = errors.New("aborted")
+
+type visitor struct {
+	ctxt  *adt.OpContext
+	visit VisitFunc
+	node  *adt.Vertex
+	err   error
+	all   bool
+	top   bool
+}
+
+// TODO: factor out the below logic as either a low-level dependency analyzer or
+// some walk functionality.
+
+// markExpr visits all nodes in an expression to mark dependencies.
+func (c *visitor) markExpr(env *adt.Environment, expr adt.Expr) {
+	switch x := expr.(type) {
+	case nil:
+	case adt.Resolver:
+		c.markResolver(env, x)
+
+	case *adt.BinaryExpr:
+		c.markExpr(env, x.X)
+		c.markExpr(env, x.Y)
+
+	case *adt.UnaryExpr:
+		c.markExpr(env, x.X)
+
+	case *adt.Interpolation:
+		for i := 1; i < len(x.Parts); i += 2 {
+			c.markExpr(env, x.Parts[i])
+		}
+
+	case *adt.BoundExpr:
+		c.markExpr(env, x.Expr)
+
+	case *adt.CallExpr:
+		c.markExpr(env, x.Fun)
+		saved := c.all
+		c.all = true
+		for _, a := range x.Args {
+			c.markExpr(env, a)
+		}
+		c.all = saved
+
+	case *adt.DisjunctionExpr:
+		for _, d := range x.Values {
+			c.markExpr(env, d.Val)
+		}
+
+	case *adt.SliceExpr:
+		c.markExpr(env, x.X)
+		c.markExpr(env, x.Lo)
+		c.markExpr(env, x.Hi)
+		c.markExpr(env, x.Stride)
+
+	case *adt.ListLit:
+		for _, e := range x.Elems {
+			switch x := e.(type) {
+			case adt.Yielder:
+				c.markYielder(env, x)
+
+			case adt.Expr:
+				c.markSubExpr(env, x)
+
+			case *adt.Ellipsis:
+				if x.Value != nil {
+					c.markSubExpr(env, x.Value)
+				}
+			}
+		}
+
+	case *adt.StructLit:
+		env := &adt.Environment{Up: env, Vertex: empty}
+		for _, e := range x.Decls {
+			c.markDecl(env, e)
+		}
+	}
+}
+
+// markResolve resolves dependencies.
+func (c *visitor) markResolver(env *adt.Environment, r adt.Resolver) {
+	switch x := r.(type) {
+	case nil:
+	case *adt.LetReference:
+		saved := c.ctxt.PushState(env, nil)
+		env := c.ctxt.Env(x.UpCount)
+		c.markExpr(env, x.X)
+		c.ctxt.PopState(saved)
+		return
+	}
+
+	if ref, _ := c.ctxt.Resolve(env, r); ref != nil {
+		if ref != c.node {
+			d := Dependency{
+				Node:      ref,
+				Reference: r,
+				top:       c.top,
+			}
+			if err := c.visit(d); err != nil {
+				c.err = err
+				panic(aborted)
+			}
+		}
+
+		return
+	}
+
+	// It is possible that a reference cannot be resolved because it is
+	// incomplete. In this case, we should check whether subexpressions of the
+	// reference can be resolved to mark those dependencies. For instance,
+	// prefix paths of selectors and the value or index of an index experssion
+	// may independently resolve to a valid dependency.
+
+	switch x := r.(type) {
+	case *adt.NodeLink:
+		panic("unreachable")
+
+	case *adt.IndexExpr:
+		c.markExpr(env, x.X)
+		c.markExpr(env, x.Index)
+
+	case *adt.SelectorExpr:
+		c.markExpr(env, x.X)
+	}
+}
+
+func (c *visitor) markSubExpr(env *adt.Environment, x adt.Expr) {
+	if c.all {
+		saved := c.top
+		c.top = false
+		c.markExpr(env, x)
+		c.top = saved
+	}
+}
+
+func (c *visitor) markDecl(env *adt.Environment, d adt.Decl) {
+	switch x := d.(type) {
+	case *adt.Field:
+		c.markSubExpr(env, x.Value)
+
+	case *adt.OptionalField:
+		// when dynamic, only continue if there is evidence of
+		// the field in the parallel actual evaluation.
+		c.markSubExpr(env, x.Value)
+
+	case *adt.BulkOptionalField:
+		c.markExpr(env, x.Filter)
+		// when dynamic, only continue if there is evidence of
+		// the field in the parallel actual evaluation.
+		c.markSubExpr(env, x.Value)
+
+	case *adt.DynamicField:
+		c.markExpr(env, x.Key)
+		// when dynamic, only continue if there is evidence of
+		// a matching field in the parallel actual evaluation.
+		c.markSubExpr(env, x.Value)
+
+	case adt.Yielder:
+		c.markYielder(env, x)
+
+	case adt.Expr:
+		c.markExpr(env, x)
+
+	case *adt.Ellipsis:
+		if x.Value != nil {
+			c.markSubExpr(env, x.Value)
+		}
+	}
+}
+
+func (c *visitor) markYielder(env *adt.Environment, y adt.Yielder) {
+	switch x := y.(type) {
+	case *adt.ForClause:
+		c.markExpr(env, x.Src)
+		env := &adt.Environment{Up: env, Vertex: empty}
+		c.markYielder(env, x.Dst)
+		// In dynamic mode, iterate over all actual value and
+		// evaluate.
+
+	case *adt.LetClause:
+		c.markExpr(env, x.Expr)
+		env := &adt.Environment{Up: env, Vertex: empty}
+		c.markYielder(env, x.Dst)
+
+	case *adt.IfClause:
+		c.markExpr(env, x.Condition)
+		// In dynamic mode, only continue if condition is true.
+		c.markYielder(env, x.Dst)
+
+	case *adt.ValueClause:
+		c.markExpr(env, x.StructLit)
+	}
+}