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|
package main
import (
"bytes"
"encoding/json"
"fmt"
"go/format"
"maps"
"slices"
"strconv"
"strings"
)
// goGen generates the Go source for a schema.
// The output is run through gofmt, so the code written here doesn't need to be indented.
type goGen struct {
pkg string
schema string
root *structType
imports map[string]bool
// regexVars are the package-level regexp declarations, in order
regexVars []string
// regexNames maps each regex pattern to its variable, so a pattern shared by fields is only compiled once
regexNames map[string]string
// regexNamesUsed are the regex variable names already declared
regexNamesUsed map[string]bool
// needsMustParse is set once a default uses a custom parse function
needsMustParse bool
}
// flagFuncs are the flag.FlagSet methods for each kind, when it isn't a custom Go type
var flagFuncs = map[kind]string{
kindBool: "BoolVar",
kindInt: "IntVar",
kindFloat: "Float64Var",
kindNumber: "Float64Var",
kindString: "StringVar",
}
const mustParseFunc = `
// mustParse applies a hand-written parse hook to a schema default. gen has
// already checked the default against the schema, so a failure here means
// the hook and the schema disagree.
func mustParse[T any](parse func(string) (T, error), s string) T {
v, err := parse(s)
if err != nil {
panic(fmt.Sprintf("schema default %q rejected by parse hook: %v", s, err))
}
return v
}
`
// genGo returns the generated Go source for root
func genGo(root *structType, pkg, schema string) ([]byte, error) {
g := &goGen{
pkg: pkg,
schema: schema,
root: root,
imports: map[string]bool{
"flag": true,
},
regexNames: make(map[string]string),
regexNamesUsed: make(map[string]bool),
}
// The body is generated first, since it decides which imports and regexes the header needs
var body bytes.Buffer
g.writeStructs(&body, root)
g.writeDefaults(&body)
g.writeRegisterFlags(&body)
g.writeValidate(&body)
if g.needsMustParse {
g.imports["fmt"] = true
body.WriteString(mustParseFunc)
}
var out bytes.Buffer
g.writeHeader(&out)
out.Write(body.Bytes())
src, err := format.Source(out.Bytes())
if err != nil {
return nil, fmt.Errorf("formatting generated Go: %w\n%s", err, out.Bytes())
}
return src, nil
}
// writeHeader writes the package clause, imports, and regex variables
func (g *goGen) writeHeader(w *bytes.Buffer) {
fmt.Fprintf(w, "// Code generated by gen from %s; DO NOT EDIT.\n\npackage %s\n\n", g.schema, g.pkg)
w.WriteString("import (\n")
for _, imp := range slices.Sorted(maps.Keys(g.imports)) {
fmt.Fprintf(w, "%q\n", imp)
}
w.WriteString(")\n")
if len(g.regexVars) > 0 {
w.WriteString("\nvar (\n")
for _, regexVar := range g.regexVars {
w.WriteString(regexVar + "\n")
}
w.WriteString(")\n")
}
}
// writeStructs writes the type declaration for st, followed by those of its nested structs
func (g *goGen) writeStructs(w *bytes.Buffer, st *structType) {
fmt.Fprintf(w, "\ntype %s struct {\n", st.goName)
for _, f := range st.fields {
// Nested structs don't get a doc comment
if f.doc != "" && f.nested == nil {
for line := range strings.SplitSeq(f.doc, "\n") {
fmt.Fprintf(w, "// %s\n", line)
}
}
fmt.Fprintf(w, "%s %s\n", f.goName, g.fieldType(f))
}
w.WriteString("}\n")
for _, f := range st.fields {
if f.nested != nil {
g.writeStructs(w, f.nested)
}
}
}
// fieldType returns the Go type of f
func (g *goGen) fieldType(f *field) string {
if f.nested != nil {
return f.nested.goName
}
if f.isList {
return "[]" + g.scalarType(f.scalar)
}
return g.scalarType(f.scalar)
}
// scalarType returns the Go type of s, adding any imports a custom type needs
func (g *goGen) scalarType(s scalar) string {
if s.customGo() {
for _, imp := range s.goImports {
g.imports[imp] = true
}
return s.goType
}
switch s.kind {
case kindBool:
return "bool"
case kindInt:
return "int"
case kindFloat, kindNumber:
return "float64"
default:
return "string"
}
}
// writeDefaults writes defaultArgs, which returns the schema's defaults
func (g *goGen) writeDefaults(w *bytes.Buffer) {
literal, _ := g.structLiteral(g.root)
fmt.Fprintf(w, `
// defaultArgs returns the defaults from %s.
func defaultArgs() %s {
return %s
}
`, g.schema, g.root.goName, literal)
}
// structLiteral returns a composite literal of st's defaults.
// Zero values are left out, and the bool reports whether anything was left in.
func (g *goGen) structLiteral(st *structType) (string, bool) {
var literal strings.Builder
hasValues := false
literal.WriteString(st.goName + "{\n")
for _, f := range st.fields {
var value string
var ok bool
switch {
case f.nested != nil:
value, ok = g.structLiteral(f.nested)
case f.hasDefault:
value, ok = g.defaultLiteral(f)
}
if ok {
fmt.Fprintf(&literal, "%s: %s,\n", f.goName, value)
hasValues = true
}
}
literal.WriteString("}")
return literal.String(), hasValues
}
// defaultLiteral returns a Go literal of f's default, or false if it's the zero value
func (g *goGen) defaultLiteral(f *field) (string, bool) {
if !f.isList {
return g.scalarLiteral(f.scalar, f.defaultValue)
}
items, _ := f.defaultValue.([]any)
if len(items) == 0 {
return "", false
}
literals := make([]string, len(items))
for idx, item := range items {
literal, ok := g.scalarLiteral(f.scalar, item)
if !ok {
// Zero values can't be left out of a list
literal = zeroLiteral(f.scalar)
}
literals[idx] = literal
}
return fmt.Sprintf("[]%s{%s}", g.scalarType(f.scalar), strings.Join(literals, ", ")), true
}
// scalarLiteral returns a Go literal of value, or false if it's the zero value
func (g *goGen) scalarLiteral(s scalar, value any) (string, bool) {
if s.customGo() {
g.needsMustParse = true
return fmt.Sprintf("mustParse(%s, %q)", s.goParse, valueString(value)), true
}
switch value := value.(type) {
case string:
return strconv.Quote(value), value != ""
case bool:
return strconv.FormatBool(value), value
case json.Number:
f, _ := value.Float64()
return value.String(), f != 0
}
return "", false
}
// zeroLiteral returns a Go literal of the zero value for s
func zeroLiteral(s scalar) string {
switch s.kind {
case kindBool:
return "false"
case kindString:
return `""`
default:
return "0"
}
}
// writeRegisterFlags writes registerFlags, which defines a flag for every field
func (g *goGen) writeRegisterFlags(w *bytes.Buffer) {
fmt.Fprintf(w, `
// registerFlags defines a flag for every field of c, using c's current
// values as flag defaults.
func registerFlags(fs *flag.FlagSet, c *%s) {
`, g.root.goName)
g.eachLeaf(g.root, "c", func(f *field, accessor string) {
name := strconv.Quote(f.flagName())
usage := strconv.Quote(usageText(f))
switch {
case f.isList:
g.writeListFlag(w, f, accessor, name, usage)
case f.scalar.customGo():
g.writeCustomFlag(w, f, accessor, name, usage)
default:
fmt.Fprintf(w, "fs.%s(&%s, %s, %s, %s)\n", flagFuncs[f.scalar.kind], accessor, name, accessor, usage)
}
})
w.WriteString("}\n")
}
// writeListFlag writes a repeatable flag, where the first use replaces the default
func (g *goGen) writeListFlag(w *bytes.Buffer, f *field, accessor, name, usage string) {
fmt.Fprintf(w, `{
set := false
fs.Func(%s, %s, func(s string) error {
`, name, usage)
g.writeParse(w, f.scalar)
fmt.Fprintf(w, ` if !set {
%[1]s, set = nil, true
}
%[1]s = append(%[1]s, v)
return nil
})
}
`, accessor)
}
// writeCustomFlag writes a flag for a custom Go type, using its parse function
func (g *goGen) writeCustomFlag(w *bytes.Buffer, f *field, accessor, name, usage string) {
fmt.Fprintf(w, "fs.Func(%s, %s, func(s string) error {\n", name, usage)
g.writeParse(w, f.scalar)
fmt.Fprintf(w, ` %s = v
return nil
})
`, accessor)
}
// writeParse writes code that parses the flag's string s into v, returning any error
func (g *goGen) writeParse(w *bytes.Buffer, s scalar) {
var call string
switch {
case s.customGo():
call = s.goParse + "(s)"
case s.kind == kindString:
w.WriteString("v := s\n")
return
case s.kind == kindBool:
g.imports["strconv"] = true
call = "strconv.ParseBool(s)"
case s.kind == kindInt:
g.imports["strconv"] = true
call = "strconv.Atoi(s)"
default:
g.imports["strconv"] = true
call = "strconv.ParseFloat(s, 64)"
}
fmt.Fprintf(w, `v, err := %s
if err != nil {
return err
}
`, call)
}
// usageText returns the flag usage for f.
// This is the first paragraph of its doc, then notes such as enum values and defaults the flag package can't show itself.
func usageText(f *field) string {
usage := strings.Join(strings.Fields(firstParagraph(f.doc)), " ")
var notes []string
if len(f.scalar.enum) > 0 {
notes = append(notes, "one of: "+joinValues(f.scalar.enum))
}
if f.isList {
notes = append(notes, "repeatable")
}
// The flag package only shows defaults of the basic flag types
if f.hasDefault && (f.isList || f.scalar.customGo()) {
if items, ok := f.defaultValue.([]any); ok {
if len(items) > 0 {
notes = append(notes, "default: "+joinValues(items))
}
} else {
notes = append(notes, "default: "+valueString(f.defaultValue))
}
}
if len(notes) == 0 {
return usage
}
if usage != "" {
usage += " "
}
return usage + "(" + strings.Join(notes, "; ") + ")"
}
// joinValues returns decoded values as a comma-separated list
func joinValues(values []any) string {
strs := make([]string, len(values))
for idx, value := range values {
strs[idx] = valueString(value)
}
return strings.Join(strs, ", ")
}
func firstParagraph(s string) string {
paragraph, _, _ := strings.Cut(s, "\n\n")
return paragraph
}
// writeValidate writes the validate method, which checks every field against its constraints
func (g *goGen) writeValidate(w *bytes.Buffer) {
var checks bytes.Buffer
g.eachLeaf(g.root, "c", func(f *field, accessor string) {
// Custom types are checked by their parse function
if f.scalar.customGo() {
return
}
g.writeFieldChecks(&checks, f, accessor)
})
fmt.Fprintf(w, `
// validate checks c against the constraints in %s.
func (c *%s) validate() error {
`, g.schema, g.root.goName)
if checks.Len() == 0 {
w.WriteString("return nil\n}\n")
return
}
g.imports["errors"] = true
g.imports["fmt"] = true
w.WriteString("var errs []error\n")
w.Write(checks.Bytes())
w.WriteString("return errors.Join(errs...)\n}\n")
}
// writeFieldChecks writes the checks for f.
// Each element of a list is checked, and an optional field is only checked when it's set.
func (g *goGen) writeFieldChecks(w *bytes.Buffer, f *field, accessor string) {
// Regex variables not named after a definition are named after the field, e.g. c.Db.URL gets reDbURL
regexName := "re" + strings.ReplaceAll(strings.TrimPrefix(accessor, "c."), ".", "")
var checks bytes.Buffer
switch {
case f.isList:
g.writeChecks(&checks, f, "v", true, regexName)
if checks.Len() > 0 {
fmt.Fprintf(w, "for i, v := range %s {\n%s}\n", accessor, checks.Bytes())
}
case f.optional:
g.writeChecks(&checks, f, accessor, false, regexName)
if checks.Len() > 0 {
fmt.Fprintf(w, "if %s != %s {\n%s}\n", accessor, zeroLiteral(f.scalar), checks.Bytes())
}
default:
g.writeChecks(w, f, accessor, false, regexName)
}
}
// writeChecks writes an if statement for each of f's constraints, which appends to errs when value breaks it.
// inList is set when value is an element of a list, indexed by i.
func (g *goGen) writeChecks(w *bytes.Buffer, f *field, value string, inList bool, regexName string) {
s := f.scalar
// Error messages are printf formats, so the flag name needs any % escaped
prefix := escapePercent(f.flagName())
var prefixArgs []string
if inList {
prefix += "[%d]"
prefixArgs = []string{"i"}
}
addCheck := func(cond, format string, args ...string) {
err := errorExpr(prefix+": "+format, append(prefixArgs, args...))
fmt.Fprintf(w, "if %s {\nerrs = append(errs, %s)\n}\n", cond, err)
}
if len(s.enum) > 0 {
g.imports["slices"] = true
literals := make([]string, len(s.enum))
for idx, e := range s.enum {
literals[idx] = valueString(e)
if str, ok := e.(string); ok {
literals[idx] = strconv.Quote(str)
}
}
verb := "%v"
if s.kind == kindString {
verb = "%q"
}
cond := fmt.Sprintf("!slices.Contains([]%s{%s}, %s)", g.scalarType(s), strings.Join(literals, ", "), value)
addCheck(cond, verb+" is not one of ["+escapePercent(joinValues(s.enum))+"]", value)
}
if s.kind == kindInt {
lower, upper := intBounds(s)
if lower != nil {
n := strconv.FormatInt(*lower, 10)
addCheck(value+" < "+n, "must be >= "+n+", got %v", value)
}
if upper != nil {
n := strconv.FormatInt(*upper, 10)
addCheck(value+" > "+n, "must be <= "+n+", got %v", value)
}
} else {
if s.min != nil {
failOp, want := "<", ">="
if !s.min.inclusive {
failOp, want = "<=", ">"
}
addCheck(value+" "+failOp+" "+s.min.value, "must be "+want+" "+s.min.value+", got %v", value)
}
if s.max != nil {
failOp, want := ">", "<="
if !s.max.inclusive {
failOp, want = ">=", "<"
}
addCheck(value+" "+failOp+" "+s.max.value, "must be "+want+" "+s.max.value+", got %v", value)
}
}
// An optional scalar is only checked when it isn't empty, so this would never fail
if s.notEmpty && (f.isList || !f.optional) {
addCheck(value+` == ""`, "must not be empty")
}
for _, re := range s.regexes {
name := g.regexVar(re, regexName)
addCheck("!"+name+".MatchString("+value+")", "%q does not match %s", value, name)
}
}
// regexVar returns the name of the variable holding re, declaring it the first time a pattern is used.
// It's named after re's definition (e.g. reURL for #URL), otherwise fieldRegexName is used.
// A number is added if the name is already taken by another pattern.
func (g *goGen) regexVar(re scalarRegex, fieldRegexName string) string {
if name, ok := g.regexNames[re.pattern]; ok {
return name
}
base := fieldRegexName
if re.goName != "" {
base = "re" + re.goName
}
name := base
for n := 2; g.regexNamesUsed[name]; n++ {
name = base + strconv.Itoa(n)
}
g.imports["regexp"] = true
g.regexNames[re.pattern] = name
g.regexNamesUsed[name] = true
g.regexVars = append(g.regexVars, fmt.Sprintf("%s = regexp.MustCompile(%q)", name, re.pattern))
return name
}
// errorExpr returns a Go expression creating an error from a printf format and the Go expressions of its args
func errorExpr(format string, args []string) string {
if len(args) == 0 {
return fmt.Sprintf("errors.New(%q)", strings.ReplaceAll(format, "%%", "%"))
}
return fmt.Sprintf("fmt.Errorf(%q, %s)", format, strings.Join(args, ", "))
}
func escapePercent(s string) string {
return strings.ReplaceAll(s, "%", "%%")
}
// eachLeaf calls fn for every non-struct field under st, along with the Go expression accessing it, e.g. c.Db.URL
func (g *goGen) eachLeaf(st *structType, accessor string, fn func(f *field, accessor string)) {
for _, f := range st.fields {
fieldAccessor := accessor + "." + f.goName
if f.nested != nil {
g.eachLeaf(f.nested, fieldAccessor, fn)
continue
}
fn(f, fieldAccessor)
}
}
|