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heuristics.go
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/
heuristics.go
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package generator
import (
"bytes"
"fmt"
"io/ioutil"
"log"
"strings"
yaml "gopkg.in/yaml.v2"
)
const (
multilinePrefix = "(?m)"
orPipe = "|"
)
// GenHeuristics generates language identification heuristics in Go.
// It is of generator.File type.
func GenHeuristics(fileToParse, _, outPath, tmplPath, tmplName, commit string) error {
heuristicsYaml, err := parseYaml(fileToParse)
if err != nil {
return err
}
langPatterns, err := loadHeuristics(heuristicsYaml)
if err != nil {
return err
}
buf := &bytes.Buffer{}
err = executeTemplate(buf, tmplName, tmplPath, commit, nil, langPatterns)
if err != nil {
return err
}
return formatedWrite(outPath, buf.Bytes())
}
// loadHeuristics transforms parsed YAML to map[".ext"]->IR for code generation.
func loadHeuristics(yaml *Heuristics) (map[string][]*LanguagePattern, error) {
patterns := make(map[string][]*LanguagePattern)
for _, disambiguation := range yaml.Disambiguations {
var rules []*LanguagePattern
for _, rule := range disambiguation.Rules {
langPattern := loadRule(yaml.NamedPatterns, rule)
if langPattern != nil {
rules = append(rules, langPattern)
}
}
// unroll to a single map
for _, ext := range disambiguation.Extensions {
if _, ok := patterns[ext]; ok {
return nil, fmt.Errorf("cannot add extension '%s', it already exists for %+v", ext, patterns[ext])
}
patterns[ext] = rules
}
}
return patterns, nil
}
// loadRule transforms single rule from parsed YAML to IR for code generation.
// For OrPattern case, it always combines multiple patterns into a single one.
func loadRule(namedPatterns map[string]StringArray, rule *Rule) *LanguagePattern {
var result *LanguagePattern
if len(rule.And) != 0 { // AndPattern
var subPatterns []*LanguagePattern
for _, r := range rule.And {
subp := loadRule(namedPatterns, r)
subPatterns = append(subPatterns, subp)
}
result = &LanguagePattern{"And", rule.Languages, "", subPatterns, true}
} else if len(rule.Pattern) != 0 { // OrPattern
// FIXME(bzz): this optimization should only be applied if each pattern isRE2!
pattern := strings.Join(rule.Pattern, orPipe)
// TODO(bzz): handle the common case Or(len(Languages)==0) better
// e.g. by emiting `rule.Rule(...)` instead of
// an (ugly) `rule.Or( rule.MatchingLanguages(""), ... )`
result = &LanguagePattern{"Or", rule.Languages, pattern, nil, isRE2(pattern)}
} else if rule.NegativePattern != "" { // NotPattern
pattern := rule.NegativePattern
result = &LanguagePattern{"Not", rule.Languages, pattern, nil, isRE2(pattern)}
} else if rule.NamedPattern != "" { // Named OrPattern
pattern := strings.Join(namedPatterns[rule.NamedPattern], orPipe)
result = &LanguagePattern{"Or", rule.Languages, pattern, nil, isRE2(pattern)}
} else { // AlwaysPattern
result = &LanguagePattern{"Always", rule.Languages, "", nil, true}
}
if !isRE2(result.Pattern) {
log.Printf("RE2 incompatible syntax for heuristic language:'%s', rule:'%s'\n", rule.Languages, result.Pattern)
}
return result
}
// LanguagePattern is an IR of parsed Rule suitable for code generations.
// Strings are used as this is to be be consumed by text/template.
type LanguagePattern struct {
Op string
Langs []string
Pattern string
Rules []*LanguagePattern
IsRE2 bool
}
type Heuristics struct {
Disambiguations []*Disambiguation
NamedPatterns map[string]StringArray `yaml:"named_patterns"`
}
type Disambiguation struct {
Extensions []string `yaml:"extensions,flow"`
Rules []*Rule `yaml:"rules"`
}
type Rule struct {
Patterns `yaml:",inline"`
Languages StringArray `yaml:"language"`
And []*Rule
}
type Patterns struct {
Pattern StringArray `yaml:"pattern,omitempty"`
NamedPattern string `yaml:"named_pattern,omitempty"`
NegativePattern string `yaml:"negative_pattern,omitempty"`
}
// StringArray is workaround for parsing named_pattern,
// wich is sometimes an array and sometimes is not.
// See https://github.com/go-yaml/yaml/issues/100
type StringArray []string
// UnmarshalYAML allows to parse element always as a []string
func (sa *StringArray) UnmarshalYAML(unmarshal func(interface{}) error) error {
var multi []string
if err := unmarshal(&multi); err != nil {
var single string
if err := unmarshal(&single); err != nil {
return err
}
*sa = []string{single}
} else {
*sa = multi
}
return nil
}
func parseYaml(file string) (*Heuristics, error) {
data, err := ioutil.ReadFile(file)
if err != nil {
return nil, err
}
h := &Heuristics{}
if err := yaml.Unmarshal(data, &h); err != nil {
return nil, err
}
return h, nil
}
// isUnsupportedRegexpSyntax filters regexp syntax that is not supported by RE2.
// In particular, we stumbled up on usage of next cases:
// - lookbehind & lookahead
// - non-backtracking subexpressions
// - named & numbered capturing group/after text matching
// - backreference
// - possessive quantifier
// For reference on supported syntax see https://github.com/google/re2/wiki/Syntax
func isUnsupportedRegexpSyntax(reg string) bool {
return strings.Contains(reg, `(?<`) || strings.Contains(reg, `(?=`) || strings.Contains(reg, `(?!`) ||
strings.Contains(reg, `(?>`) || strings.Contains(reg, `\1`) || strings.Contains(reg, `*+`) ||
// See https://github.com/github/linguist/pull/4243#discussion_r246105067
(strings.HasPrefix(reg, multilinePrefix+`/`) && strings.HasSuffix(reg, `/`))
}
func isRE2(s string) bool {
return !isUnsupportedRegexpSyntax(s)
}