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-rw-r--r--src/internal/dag/parse.go314
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+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package dag implements a language for expressing directed acyclic
+// graphs.
+//
+// The general syntax of a rule is:
+//
+// a, b < c, d;
+//
+// which means c and d come after a and b in the partial order
+// (that is, there are edges from c and d to a and b),
+// but doesn't provide a relative order between a vs b or c vs d.
+//
+// The rules can chain together, as in:
+//
+// e < f, g < h;
+//
+// which is equivalent to
+//
+// e < f, g;
+// f, g < h;
+//
+// Except for the special bottom element "NONE", each name
+// must appear exactly once on the right-hand side of any rule.
+// That rule serves as the definition of the allowed successor
+// for that name. The definition must appear before any uses
+// of the name on the left-hand side of a rule. (That is, the
+// rules themselves must be ordered according to the partial
+// order, for easier reading by people.)
+//
+// Negative assertions double-check the partial order:
+//
+// i !< j
+//
+// means that it must NOT be the case that i < j.
+// Negative assertions may appear anywhere in the rules,
+// even before i and j have been defined.
+//
+// Comments begin with #.
+package dag
+
+import (
+ "fmt"
+ "sort"
+ "strings"
+)
+
+type Graph struct {
+ Nodes []string
+ byLabel map[string]int
+ edges map[string]map[string]bool
+}
+
+func newGraph() *Graph {
+ return &Graph{byLabel: map[string]int{}, edges: map[string]map[string]bool{}}
+}
+
+func (g *Graph) addNode(label string) bool {
+ if _, ok := g.byLabel[label]; ok {
+ return false
+ }
+ g.byLabel[label] = len(g.Nodes)
+ g.Nodes = append(g.Nodes, label)
+ g.edges[label] = map[string]bool{}
+ return true
+}
+
+func (g *Graph) AddEdge(from, to string) {
+ g.edges[from][to] = true
+}
+
+func (g *Graph) DelEdge(from, to string) {
+ delete(g.edges[from], to)
+}
+
+func (g *Graph) HasEdge(from, to string) bool {
+ return g.edges[from] != nil && g.edges[from][to]
+}
+
+func (g *Graph) Edges(from string) []string {
+ edges := make([]string, 0, 16)
+ for k := range g.edges[from] {
+ edges = append(edges, k)
+ }
+ sort.Slice(edges, func(i, j int) bool { return g.byLabel[edges[i]] < g.byLabel[edges[j]] })
+ return edges
+}
+
+// Parse parses the DAG language and returns the transitive closure of
+// the described graph. In the returned graph, there is an edge from "b"
+// to "a" if b < a (or a > b) in the partial order.
+func Parse(dag string) (*Graph, error) {
+ g := newGraph()
+ disallowed := []rule{}
+
+ rules, err := parseRules(dag)
+ if err != nil {
+ return nil, err
+ }
+
+ // TODO: Add line numbers to errors.
+ var errors []string
+ errorf := func(format string, a ...any) {
+ errors = append(errors, fmt.Sprintf(format, a...))
+ }
+ for _, r := range rules {
+ if r.op == "!<" {
+ disallowed = append(disallowed, r)
+ continue
+ }
+ for _, def := range r.def {
+ if def == "NONE" {
+ errorf("NONE cannot be a predecessor")
+ continue
+ }
+ if !g.addNode(def) {
+ errorf("multiple definitions for %s", def)
+ }
+ for _, less := range r.less {
+ if less == "NONE" {
+ continue
+ }
+ if _, ok := g.byLabel[less]; !ok {
+ errorf("use of %s before its definition", less)
+ } else {
+ g.AddEdge(def, less)
+ }
+ }
+ }
+ }
+
+ // Check for missing definition.
+ for _, tos := range g.edges {
+ for to := range tos {
+ if g.edges[to] == nil {
+ errorf("missing definition for %s", to)
+ }
+ }
+ }
+
+ // Complete transitive closure.
+ for _, k := range g.Nodes {
+ for _, i := range g.Nodes {
+ for _, j := range g.Nodes {
+ if i != k && k != j && g.HasEdge(i, k) && g.HasEdge(k, j) {
+ if i == j {
+ // Can only happen along with a "use of X before deps" error above,
+ // but this error is more specific - it makes clear that reordering the
+ // rules will not be enough to fix the problem.
+ errorf("graph cycle: %s < %s < %s", j, k, i)
+ }
+ g.AddEdge(i, j)
+ }
+ }
+ }
+ }
+
+ // Check negative assertions against completed allowed graph.
+ for _, bad := range disallowed {
+ for _, less := range bad.less {
+ for _, def := range bad.def {
+ if g.HasEdge(def, less) {
+ errorf("graph edge assertion failed: %s !< %s", less, def)
+ }
+ }
+ }
+ }
+
+ if len(errors) > 0 {
+ return nil, fmt.Errorf("%s", strings.Join(errors, "\n"))
+ }
+
+ return g, nil
+}
+
+// A rule is a line in the DAG language where "less < def" or "less !< def".
+type rule struct {
+ less []string
+ op string // Either "<" or "!<"
+ def []string
+}
+
+type syntaxError string
+
+func (e syntaxError) Error() string {
+ return string(e)
+}
+
+// parseRules parses the rules of a DAG.
+func parseRules(rules string) (out []rule, err error) {
+ defer func() {
+ e := recover()
+ switch e := e.(type) {
+ case nil:
+ return
+ case syntaxError:
+ err = e
+ default:
+ panic(e)
+ }
+ }()
+ p := &rulesParser{lineno: 1, text: rules}
+
+ var prev []string
+ var op string
+ for {
+ list, tok := p.nextList()
+ if tok == "" {
+ if prev == nil {
+ break
+ }
+ p.syntaxError("unexpected EOF")
+ }
+ if prev != nil {
+ out = append(out, rule{prev, op, list})
+ }
+ prev = list
+ if tok == ";" {
+ prev = nil
+ op = ""
+ continue
+ }
+ if tok != "<" && tok != "!<" {
+ p.syntaxError("missing <")
+ }
+ op = tok
+ }
+
+ return out, err
+}
+
+// A rulesParser parses the depsRules syntax described above.
+type rulesParser struct {
+ lineno int
+ lastWord string
+ text string
+}
+
+// syntaxError reports a parsing error.
+func (p *rulesParser) syntaxError(msg string) {
+ panic(syntaxError(fmt.Sprintf("parsing graph: line %d: syntax error: %s near %s", p.lineno, msg, p.lastWord)))
+}
+
+// nextList parses and returns a comma-separated list of names.
+func (p *rulesParser) nextList() (list []string, token string) {
+ for {
+ tok := p.nextToken()
+ switch tok {
+ case "":
+ if len(list) == 0 {
+ return nil, ""
+ }
+ fallthrough
+ case ",", "<", "!<", ";":
+ p.syntaxError("bad list syntax")
+ }
+ list = append(list, tok)
+
+ tok = p.nextToken()
+ if tok != "," {
+ return list, tok
+ }
+ }
+}
+
+// nextToken returns the next token in the deps rules,
+// one of ";" "," "<" "!<" or a name.
+func (p *rulesParser) nextToken() string {
+ for {
+ if p.text == "" {
+ return ""
+ }
+ switch p.text[0] {
+ case ';', ',', '<':
+ t := p.text[:1]
+ p.text = p.text[1:]
+ return t
+
+ case '!':
+ if len(p.text) < 2 || p.text[1] != '<' {
+ p.syntaxError("unexpected token !")
+ }
+ p.text = p.text[2:]
+ return "!<"
+
+ case '#':
+ i := strings.Index(p.text, "\n")
+ if i < 0 {
+ i = len(p.text)
+ }
+ p.text = p.text[i:]
+ continue
+
+ case '\n':
+ p.lineno++
+ fallthrough
+ case ' ', '\t':
+ p.text = p.text[1:]
+ continue
+
+ default:
+ i := strings.IndexAny(p.text, "!;,<#\n \t")
+ if i < 0 {
+ i = len(p.text)
+ }
+ t := p.text[:i]
+ p.text = p.text[i:]
+ p.lastWord = t
+ return t
+ }
+ }
+}