Support Issue forms and PR forms (#20987)

* feat: extend issue template for yaml

* feat: support yaml template

* feat: render form to markdown

* feat: support yaml template for pr

* chore: rename to Fields

* feat: template unmarshal

* feat: split template

* feat: render to markdown

* feat: use full name as template file name

* chore: remove useless file

* feat: use dropdown of fomantic ui

* feat: update input style

* docs: more comments

* fix: render text without render

* chore: fix lint error

* fix: support use description as about in markdown

* fix: add field class in form

* chore: generate swagger

* feat: validate template

* feat: support is_nummber and regex

* test: fix broken unit tests

* fix: ignore empty body of md template

* fix: make multiple easymde editors work in one page

* feat: better UI

* fix: js error in pr form

* chore: generate swagger

* feat: support regex validation

* chore: generate swagger

* fix: refresh each markdown editor

* chore: give up required validation

* fix: correct issue template candidates

* fix: correct checkboxes style

* chore: ignore .hugo_build.lock in docs

* docs: separate out a new doc for merge templates

* docs: introduce syntax of yaml template

* feat: show a alert for invalid templates

* test: add case for a valid template

* fix: correct attributes of required checkbox

* fix: add class not-under-easymde for dropzone

* fix: use more back-quotes

* chore: remove translation in zh-CN

* fix EasyMDE statusbar margin

* fix: remove repeated blocks

* fix: reuse regex for quotes

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

6 files changed, 1250 insertions, 58 deletions

diff --git a/modules/context/repo.go b/modules/context/repo.go
index 5404acc05a..6a336c45f7 100644
--- a/modules/context/repo.go
+++ b/modules/context/repo.go
@@ -9,7 +9,6 @@ import (
 	"context"
 	"fmt"
 	"html"
-	"io"
 	"net/http"
 	"net/url"
 	"path"
@@ -26,8 +25,8 @@ import (
 	"code.gitea.io/gitea/modules/cache"
 	"code.gitea.io/gitea/modules/git"
 	code_indexer "code.gitea.io/gitea/modules/indexer/code"
+	"code.gitea.io/gitea/modules/issue/template"
 	"code.gitea.io/gitea/modules/log"
-	"code.gitea.io/gitea/modules/markup/markdown"
 	repo_module "code.gitea.io/gitea/modules/repository"
 	"code.gitea.io/gitea/modules/setting"
 	api "code.gitea.io/gitea/modules/structs"
@@ -1034,70 +1033,52 @@ func UnitTypes() func(ctx *Context) {
 	}
 }
 
-// IssueTemplatesFromDefaultBranch checks for issue templates in the repo's default branch
-func (ctx *Context) IssueTemplatesFromDefaultBranch() []api.IssueTemplate {
-	var issueTemplates []api.IssueTemplate
+// IssueTemplatesFromDefaultBranch checks for valid issue templates in the repo's default branch,
+func (ctx *Context) IssueTemplatesFromDefaultBranch() []*api.IssueTemplate {
+	ret, _ := ctx.IssueTemplatesErrorsFromDefaultBranch()
+	return ret
+}
+
+// IssueTemplatesErrorsFromDefaultBranch checks for issue templates in the repo's default branch,
+// returns valid templates and the errors of invalid template files.
+func (ctx *Context) IssueTemplatesErrorsFromDefaultBranch() ([]*api.IssueTemplate, map[string]error) {
+	var issueTemplates []*api.IssueTemplate
 
 	if ctx.Repo.Repository.IsEmpty {
-		return issueTemplates
+		return issueTemplates, nil
 	}
 
 	if ctx.Repo.Commit == nil {
 		var err error
 		ctx.Repo.Commit, err = ctx.Repo.GitRepo.GetBranchCommit(ctx.Repo.Repository.DefaultBranch)
 		if err != nil {
-			return issueTemplates
+			return issueTemplates, nil
 		}
 	}
 
+	invalidFiles := map[string]error{}
 	for _, dirName := range IssueTemplateDirCandidates {
 		tree, err := ctx.Repo.Commit.SubTree(dirName)
 		if err != nil {
+			log.Debug("get sub tree of %s: %v", dirName, err)
 			continue
 		}
 		entries, err := tree.ListEntries()
 		if err != nil {
-			return issueTemplates
+			log.Debug("list entries in %s: %v", dirName, err)
+			return issueTemplates, nil
 		}
 		for _, entry := range entries {
-			if strings.HasSuffix(entry.Name(), ".md") {
-				if entry.Blob().Size() >= setting.UI.MaxDisplayFileSize {
-					log.Debug("Issue template is too large: %s", entry.Name())
-					continue
-				}
-				r, err := entry.Blob().DataAsync()
-				if err != nil {
-					log.Debug("DataAsync: %v", err)
-					continue
-				}
-				closed := false
-				defer func() {
-					if !closed {
-						_ = r.Close()
-					}
-				}()
-				data, err := io.ReadAll(r)
-				if err != nil {
-					log.Debug("ReadAll: %v", err)
-					continue
-				}
-				_ = r.Close()
-				var it api.IssueTemplate
-				content, err := markdown.ExtractMetadata(string(data), &it)
-				if err != nil {
-					log.Debug("ExtractMetadata: %v", err)
-					continue
-				}
-				it.Content = content
-				it.FileName = entry.Name()
-				if it.Valid() {
-					issueTemplates = append(issueTemplates, it)
-				}
+			if !template.CouldBe(entry.Name()) {
+				continue
+			}
+			fullName := path.Join(dirName, entry.Name())
+			if it, err := template.UnmarshalFromEntry(entry, dirName); err != nil {
+				invalidFiles[fullName] = err
+			} else {
+				issueTemplates = append(issueTemplates, it)
 			}
-		}
-		if len(issueTemplates) > 0 {
-			return issueTemplates
 		}
 	}
-	return issueTemplates
+	return issueTemplates, invalidFiles
 }
diff --git a/modules/issue/template/template.go b/modules/issue/template/template.go
new file mode 100644
index 0000000000..a4c0fb5aa6
--- /dev/null
+++ b/modules/issue/template/template.go
@@ -0,0 +1,392 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package template
+
+import (
+	"fmt"
+	"net/url"
+	"regexp"
+	"strconv"
+	"strings"
+
+	api "code.gitea.io/gitea/modules/structs"
+
+	"gitea.com/go-chi/binding"
+)
+
+// Validate checks whether an IssueTemplate is considered valid, and returns the first error
+func Validate(template *api.IssueTemplate) error {
+	if err := validateMetadata(template); err != nil {
+		return err
+	}
+	if template.Type() == api.IssueTemplateTypeYaml {
+		if err := validateYaml(template); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func validateMetadata(template *api.IssueTemplate) error {
+	if strings.TrimSpace(template.Name) == "" {
+		return fmt.Errorf("'name' is required")
+	}
+	if strings.TrimSpace(template.About) == "" {
+		return fmt.Errorf("'about' is required")
+	}
+	return nil
+}
+
+func validateYaml(template *api.IssueTemplate) error {
+	if len(template.Fields) == 0 {
+		return fmt.Errorf("'body' is required")
+	}
+	ids := map[string]struct{}{}
+	for idx, field := range template.Fields {
+		if err := validateID(field, idx, ids); err != nil {
+			return err
+		}
+		if err := validateLabel(field, idx); err != nil {
+			return err
+		}
+
+		position := newErrorPosition(idx, field.Type)
+		switch field.Type {
+		case api.IssueFormFieldTypeMarkdown:
+			if err := validateStringItem(position, field.Attributes, true, "value"); err != nil {
+				return err
+			}
+		case api.IssueFormFieldTypeTextarea:
+			if err := validateStringItem(position, field.Attributes, false,
+				"description",
+				"placeholder",
+				"value",
+				"render",
+			); err != nil {
+				return err
+			}
+		case api.IssueFormFieldTypeInput:
+			if err := validateStringItem(position, field.Attributes, false,
+				"description",
+				"placeholder",
+				"value",
+			); err != nil {
+				return err
+			}
+			if err := validateBoolItem(position, field.Validations, "is_number"); err != nil {
+				return err
+			}
+			if err := validateStringItem(position, field.Validations, false, "regex"); err != nil {
+				return err
+			}
+		case api.IssueFormFieldTypeDropdown:
+			if err := validateStringItem(position, field.Attributes, false, "description"); err != nil {
+				return err
+			}
+			if err := validateBoolItem(position, field.Attributes, "multiple"); err != nil {
+				return err
+			}
+			if err := validateOptions(field, idx); err != nil {
+				return err
+			}
+		case api.IssueFormFieldTypeCheckboxes:
+			if err := validateStringItem(position, field.Attributes, false, "description"); err != nil {
+				return err
+			}
+			if err := validateOptions(field, idx); err != nil {
+				return err
+			}
+		default:
+			return position.Errorf("unknown type")
+		}
+
+		if err := validateRequired(field, idx); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func validateLabel(field *api.IssueFormField, idx int) error {
+	if field.Type == api.IssueFormFieldTypeMarkdown {
+		// The label is not required for a markdown field
+		return nil
+	}
+	return validateStringItem(newErrorPosition(idx, field.Type), field.Attributes, true, "label")
+}
+
+func validateRequired(field *api.IssueFormField, idx int) error {
+	if field.Type == api.IssueFormFieldTypeMarkdown || field.Type == api.IssueFormFieldTypeCheckboxes {
+		// The label is not required for a markdown or checkboxes field
+		return nil
+	}
+	return validateBoolItem(newErrorPosition(idx, field.Type), field.Validations, "required")
+}
+
+func validateID(field *api.IssueFormField, idx int, ids map[string]struct{}) error {
+	if field.Type == api.IssueFormFieldTypeMarkdown {
+		// The ID is not required for a markdown field
+		return nil
+	}
+
+	position := newErrorPosition(idx, field.Type)
+	if field.ID == "" {
+		// If the ID is empty in yaml, template.Unmarshal will auto autofill it, so it cannot be empty
+		return position.Errorf("'id' is required")
+	}
+	if binding.AlphaDashPattern.MatchString(field.ID) {
+		return position.Errorf("'id' should contain only alphanumeric, '-' and '_'")
+	}
+	if _, ok := ids[field.ID]; ok {
+		return position.Errorf("'id' should be unique")
+	}
+	ids[field.ID] = struct{}{}
+	return nil
+}
+
+func validateOptions(field *api.IssueFormField, idx int) error {
+	if field.Type != api.IssueFormFieldTypeDropdown && field.Type != api.IssueFormFieldTypeCheckboxes {
+		return nil
+	}
+	position := newErrorPosition(idx, field.Type)
+
+	options, ok := field.Attributes["options"].([]interface{})
+	if !ok || len(options) == 0 {
+		return position.Errorf("'options' is required and should be a array")
+	}
+
+	for optIdx, option := range options {
+		position := newErrorPosition(idx, field.Type, optIdx)
+		switch field.Type {
+		case api.IssueFormFieldTypeDropdown:
+			if _, ok := option.(string); !ok {
+				return position.Errorf("should be a string")
+			}
+		case api.IssueFormFieldTypeCheckboxes:
+			opt, ok := option.(map[interface{}]interface{})
+			if !ok {
+				return position.Errorf("should be a dictionary")
+			}
+			if label, ok := opt["label"].(string); !ok || label == "" {
+				return position.Errorf("'label' is required and should be a string")
+			}
+
+			if required, ok := opt["required"]; ok {
+				if _, ok := required.(bool); !ok {
+					return position.Errorf("'required' should be a bool")
+				}
+			}
+		}
+	}
+	return nil
+}
+
+func validateStringItem(position errorPosition, m map[string]interface{}, required bool, names ...string) error {
+	for _, name := range names {
+		v, ok := m[name]
+		if !ok {
+			if required {
+				return position.Errorf("'%s' is required", name)
+			}
+			return nil
+		}
+		attr, ok := v.(string)
+		if !ok {
+			return position.Errorf("'%s' should be a string", name)
+		}
+		if strings.TrimSpace(attr) == "" && required {
+			return position.Errorf("'%s' is required", name)
+		}
+	}
+	return nil
+}
+
+func validateBoolItem(position errorPosition, m map[string]interface{}, names ...string) error {
+	for _, name := range names {
+		v, ok := m[name]
+		if !ok {
+			return nil
+		}
+		if _, ok := v.(bool); !ok {
+			return position.Errorf("'%s' should be a bool", name)
+		}
+	}
+	return nil
+}
+
+type errorPosition string
+
+func (p errorPosition) Errorf(format string, a ...interface{}) error {
+	return fmt.Errorf(string(p)+": "+format, a...)
+}
+
+func newErrorPosition(fieldIdx int, fieldType api.IssueFormFieldType, optionIndex ...int) errorPosition {
+	ret := fmt.Sprintf("body[%d](%s)", fieldIdx, fieldType)
+	if len(optionIndex) > 0 {
+		ret += fmt.Sprintf(", option[%d]", optionIndex[0])
+	}
+	return errorPosition(ret)
+}
+
+// RenderToMarkdown renders template to markdown with specified values
+func RenderToMarkdown(template *api.IssueTemplate, values url.Values) string {
+	builder := &strings.Builder{}
+
+	for _, field := range template.Fields {
+		f := &valuedField{
+			IssueFormField: field,
+			Values:         values,
+		}
+		if f.ID == "" {
+			continue
+		}
+		f.WriteTo(builder)
+	}
+
+	return builder.String()
+}
+
+type valuedField struct {
+	*api.IssueFormField
+	url.Values
+}
+
+func (f *valuedField) WriteTo(builder *strings.Builder) {
+	if f.Type == api.IssueFormFieldTypeMarkdown {
+		// markdown blocks do not appear in output
+		return
+	}
+
+	// write label
+	_, _ = fmt.Fprintf(builder, "### %s\n\n", f.Label())
+
+	blankPlaceholder := "_No response_\n"
+
+	// write body
+	switch f.Type {
+	case api.IssueFormFieldTypeCheckboxes:
+		for _, option := range f.Options() {
+			checked := " "
+			if option.IsChecked() {
+				checked = "x"
+			}
+			_, _ = fmt.Fprintf(builder, "- [%s] %s\n", checked, option.Label())
+		}
+	case api.IssueFormFieldTypeDropdown:
+		var checkeds []string
+		for _, option := range f.Options() {
+			if option.IsChecked() {
+				checkeds = append(checkeds, option.Label())
+			}
+		}
+		if len(checkeds) > 0 {
+			_, _ = fmt.Fprintf(builder, "%s\n", strings.Join(checkeds, ", "))
+		} else {
+			_, _ = fmt.Fprint(builder, blankPlaceholder)
+		}
+	case api.IssueFormFieldTypeInput:
+		if value := f.Value(); value == "" {
+			_, _ = fmt.Fprint(builder, blankPlaceholder)
+		} else {
+			_, _ = fmt.Fprintf(builder, "%s\n", value)
+		}
+	case api.IssueFormFieldTypeTextarea:
+		if value := f.Value(); value == "" {
+			_, _ = fmt.Fprint(builder, blankPlaceholder)
+		} else if render := f.Render(); render != "" {
+			quotes := minQuotes(value)
+			_, _ = fmt.Fprintf(builder, "%s%s\n%s\n%s\n", quotes, f.Render(), value, quotes)
+		} else {
+			_, _ = fmt.Fprintf(builder, "%s\n", value)
+		}
+	}
+	_, _ = fmt.Fprintln(builder)
+}
+
+func (f *valuedField) Label() string {
+	if label, ok := f.Attributes["label"].(string); ok {
+		return label
+	}
+	return ""
+}
+
+func (f *valuedField) Render() string {
+	if render, ok := f.Attributes["render"].(string); ok {
+		return render
+	}
+	return ""
+}
+
+func (f *valuedField) Value() string {
+	return strings.TrimSpace(f.Get(fmt.Sprintf("form-field-" + f.ID)))
+}
+
+func (f *valuedField) Options() []*valuedOption {
+	if options, ok := f.Attributes["options"].([]interface{}); ok {
+		ret := make([]*valuedOption, 0, len(options))
+		for i, option := range options {
+			ret = append(ret, &valuedOption{
+				index: i,
+				data:  option,
+				field: f,
+			})
+		}
+		return ret
+	}
+	return nil
+}
+
+type valuedOption struct {
+	index int
+	data  interface{}
+	field *valuedField
+}
+
+func (o *valuedOption) Label() string {
+	switch o.field.Type {
+	case api.IssueFormFieldTypeDropdown:
+		if label, ok := o.data.(string); ok {
+			return label
+		}
+	case api.IssueFormFieldTypeCheckboxes:
+		if vs, ok := o.data.(map[interface{}]interface{}); ok {
+			if v, ok := vs["label"].(string); ok {
+				return v
+			}
+		}
+	}
+	return ""
+}
+
+func (o *valuedOption) IsChecked() bool {
+	switch o.field.Type {
+	case api.IssueFormFieldTypeDropdown:
+		checks := strings.Split(o.field.Get(fmt.Sprintf("form-field-%s", o.field.ID)), ",")
+		idx := strconv.Itoa(o.index)
+		for _, v := range checks {
+			if v == idx {
+				return true
+			}
+		}
+		return false
+	case api.IssueFormFieldTypeCheckboxes:
+		return o.field.Get(fmt.Sprintf("form-field-%s-%d", o.field.ID, o.index)) == "on"
+	}
+	return false
+}
+
+var minQuotesRegex = regexp.MustCompilePOSIX("^`{3,}")
+
+// minQuotes return 3 or more back-quotes.
+// If n back-quotes exists, use n+1 back-quotes to quote.
+func minQuotes(value string) string {
+	ret := "```"
+	for _, v := range minQuotesRegex.FindAllString(value, -1) {
+		if len(v) >= len(ret) {
+			ret = v + "`"
+		}
+	}
+	return ret
+}
diff --git a/modules/issue/template/template_test.go b/modules/issue/template/template_test.go
new file mode 100644
index 0000000000..883e1e0780
--- /dev/null
+++ b/modules/issue/template/template_test.go
@@ -0,0 +1,645 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package template
+
+import (
+	"net/url"
+	"reflect"
+	"testing"
+
+	"code.gitea.io/gitea/modules/json"
+	api "code.gitea.io/gitea/modules/structs"
+)
+
+func TestValidate(t *testing.T) {
+	tests := []struct {
+		name    string
+		content string
+		wantErr string
+	}{
+		{
+			name:    "miss name",
+			content: ``,
+			wantErr: "'name' is required",
+		},
+		{
+			name: "miss about",
+			content: `
+name: "test"
+`,
+			wantErr: "'about' is required",
+		},
+		{
+			name: "miss body",
+			content: `
+name: "test"
+about: "this is about"
+`,
+			wantErr: "'body' is required",
+		},
+		{
+			name: "markdown miss value",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "markdown"
+`,
+			wantErr: "body[0](markdown): 'value' is required",
+		},
+		{
+			name: "markdown invalid value",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "markdown"
+    attributes:
+      value: true
+`,
+			wantErr: "body[0](markdown): 'value' should be a string",
+		},
+		{
+			name: "markdown empty value",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "markdown"
+    attributes:
+      value: ""
+`,
+			wantErr: "body[0](markdown): 'value' is required",
+		},
+		{
+			name: "textarea invalid id",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "textarea"
+    id: "?"
+`,
+			wantErr: "body[0](textarea): 'id' should contain only alphanumeric, '-' and '_'",
+		},
+		{
+			name: "textarea miss label",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "textarea"
+    id: "1"
+`,
+			wantErr: "body[0](textarea): 'label' is required",
+		},
+		{
+			name: "textarea conflict id",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "textarea"
+    id: "1"
+    attributes:
+      label: "a"
+  - type: "textarea"
+    id: "1"
+    attributes:
+      label: "b"
+`,
+			wantErr: "body[1](textarea): 'id' should be unique",
+		},
+		{
+			name: "textarea invalid description",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "textarea"
+    id: "1"
+    attributes:
+      label: "a"
+      description: true
+`,
+			wantErr: "body[0](textarea): 'description' should be a string",
+		},
+		{
+			name: "textarea invalid required",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "textarea"
+    id: "1"
+    attributes:
+      label: "a"
+    validations:
+      required: "on"
+`,
+			wantErr: "body[0](textarea): 'required' should be a bool",
+		},
+		{
+			name: "input invalid description",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "input"
+    id: "1"
+    attributes:
+      label: "a"
+      description: true
+`,
+			wantErr: "body[0](input): 'description' should be a string",
+		},
+		{
+			name: "input invalid is_number",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "input"
+    id: "1"
+    attributes:
+      label: "a"
+    validations:
+      is_number: "yes"
+`,
+			wantErr: "body[0](input): 'is_number' should be a bool",
+		},
+		{
+			name: "input invalid regex",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "input"
+    id: "1"
+    attributes:
+      label: "a"
+    validations:
+      regex: true
+`,
+			wantErr: "body[0](input): 'regex' should be a string",
+		},
+		{
+			name: "dropdown invalid description",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "dropdown"
+    id: "1"
+    attributes:
+      label: "a"
+      description: true
+`,
+			wantErr: "body[0](dropdown): 'description' should be a string",
+		},
+		{
+			name: "dropdown invalid multiple",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "dropdown"
+    id: "1"
+    attributes:
+      label: "a"
+      multiple: "on"
+`,
+			wantErr: "body[0](dropdown): 'multiple' should be a bool",
+		},
+		{
+			name: "checkboxes invalid description",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "checkboxes"
+    id: "1"
+    attributes:
+      label: "a"
+      description: true
+`,
+			wantErr: "body[0](checkboxes): 'description' should be a string",
+		},
+		{
+			name: "invalid type",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "video"
+    id: "1"
+    attributes:
+      label: "a"
+`,
+			wantErr: "body[0](video): unknown type",
+		},
+		{
+			name: "dropdown miss options",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "dropdown"
+    id: "1"
+    attributes:
+      label: "a"
+`,
+			wantErr: "body[0](dropdown): 'options' is required and should be a array",
+		},
+		{
+			name: "dropdown invalid options",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "dropdown"
+    id: "1"
+    attributes:
+      label: "a"
+      options:
+        - "a"
+        - true
+`,
+			wantErr: "body[0](dropdown), option[1]: should be a string",
+		},
+		{
+			name: "checkboxes invalid options",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "checkboxes"
+    id: "1"
+    attributes:
+      label: "a"
+      options:
+        - "a"
+        - true
+`,
+			wantErr: "body[0](checkboxes), option[0]: should be a dictionary",
+		},
+		{
+			name: "checkboxes option miss label",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "checkboxes"
+    id: "1"
+    attributes:
+      label: "a"
+      options:
+        - required: true
+`,
+			wantErr: "body[0](checkboxes), option[0]: 'label' is required and should be a string",
+		},
+		{
+			name: "checkboxes option invalid required",
+			content: `
+name: "test"
+about: "this is about"
+body:
+  - type: "checkboxes"
+    id: "1"
+    attributes:
+      label: "a"
+      options:
+        - label: "a"
+          required: "on"
+`,
+			wantErr: "body[0](checkboxes), option[0]: 'required' should be a bool",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tmpl, err := unmarshal("test.yaml", []byte(tt.content))
+			if err != nil {
+				t.Fatal(err)
+			}
+			if err := Validate(tmpl); (err == nil) != (tt.wantErr == "") || err != nil && err.Error() != tt.wantErr {
+				t.Errorf("Validate() error = %v, wantErr %q", err, tt.wantErr)
+			}
+		})
+	}
+
+	t.Run("valid", func(t *testing.T) {
+		content := `
+name: Name
+title: Title
+about: About
+labels: ["label1", "label2"]
+ref: Ref
+body:
+  - type: markdown
+    id: id1
+    attributes:
+      value: Value of the markdown
+  - type: textarea
+    id: id2
+    attributes:
+      label: Label of textarea
+      description: Description of textarea
+      placeholder: Placeholder of textarea
+      value: Value of textarea
+      render: bash
+    validations:
+      required: true
+  - type: input
+    id: id3
+    attributes:
+      label: Label of input
+      description: Description of input
+      placeholder: Placeholder of input
+      value: Value of input
+    validations:
+      required: true
+      is_number: true
+      regex: "[a-zA-Z0-9]+"
+  - type: dropdown
+    id: id4
+    attributes:
+      label: Label of dropdown
+      description: Description of dropdown
+      multiple: true
+      options:
+        - Option 1 of dropdown
+        - Option 2 of dropdown
+        - Option 3 of dropdown
+    validations:
+      required: true
+  - type: checkboxes
+    id: id5
+    attributes:
+      label: Label of checkboxes
+      description: Description of checkboxes
+      options:
+        - label: Option 1 of checkboxes
+          required: true
+        - label: Option 2 of checkboxes
+          required: false
+        - label: Option 3 of checkboxes
+          required: true
+`
+		want := &api.IssueTemplate{
+			Name:   "Name",
+			Title:  "Title",
+			About:  "About",
+			Labels: []string{"label1", "label2"},
+			Ref:    "Ref",
+			Fields: []*api.IssueFormField{
+				{
+					Type: "markdown",
+					ID:   "id1",
+					Attributes: map[string]interface{}{
+						"value": "Value of the markdown",
+					},
+				},
+				{
+					Type: "textarea",
+					ID:   "id2",
+					Attributes: map[string]interface{}{
+						"label":       "Label of textarea",
+						"description": "Description of textarea",
+						"placeholder": "Placeholder of textarea",
+						"value":       "Value of textarea",
+						"render":      "bash",
+					},
+					Validations: map[string]interface{}{
+						"required": true,
+					},
+				},
+				{
+					Type: "input",
+					ID:   "id3",
+					Attributes: map[string]interface{}{
+						"label":       "Label of input",
+						"description": "Description of input",
+						"placeholder": "Placeholder of input",
+						"value":       "Value of input",
+					},
+					Validations: map[string]interface{}{
+						"required":  true,
+						"is_number": true,
+						"regex":     "[a-zA-Z0-9]+",
+					},
+				},
+				{
+					Type: "dropdown",
+					ID:   "id4",
+					Attributes: map[string]interface{}{
+						"label":       "Label of dropdown",
+						"description": "Description of dropdown",
+						"multiple":    true,
+						"options": []interface{}{
+							"Option 1 of dropdown",
+							"Option 2 of dropdown",
+							"Option 3 of dropdown",
+						},
+					},
+					Validations: map[string]interface{}{
+						"required": true,
+					},
+				},
+				{
+					Type: "checkboxes",
+					ID:   "id5",
+					Attributes: map[string]interface{}{
+						"label":       "Label of checkboxes",
+						"description": "Description of checkboxes",
+						"options": []interface{}{
+							map[interface{}]interface{}{"label": "Option 1 of checkboxes", "required": true},
+							map[interface{}]interface{}{"label": "Option 2 of checkboxes", "required": false},
+							map[interface{}]interface{}{"label": "Option 3 of checkboxes", "required": true},
+						},
+					},
+				},
+			},
+			FileName: "test.yaml",
+		}
+		got, err := unmarshal("test.yaml", []byte(content))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := Validate(got); err != nil {
+			t.Errorf("Validate() error = %v", err)
+		}
+		if !reflect.DeepEqual(want, got) {
+			jsonWant, _ := json.Marshal(want)
+			jsonGot, _ := json.Marshal(got)
+			t.Errorf("want:\n%s\ngot:\n%s", jsonWant, jsonGot)
+		}
+	})
+}
+
+func TestRenderToMarkdown(t *testing.T) {
+	type args struct {
+		template string
+		values   url.Values
+	}
+	tests := []struct {
+		name string
+		args args
+		want string
+	}{
+		{
+			name: "normal",
+			args: args{
+				template: `
+name: Name
+title: Title
+about: About
+labels: ["label1", "label2"]
+ref: Ref
+body:
+  - type: markdown
+    id: id1
+    attributes:
+      value: Value of the markdown
+  - type: textarea
+    id: id2
+    attributes:
+      label: Label of textarea
+      description: Description of textarea
+      placeholder: Placeholder of textarea
+      value: Value of textarea
+      render: bash
+    validations:
+      required: true
+  - type: input
+    id: id3
+    attributes:
+      label: Label of input
+      description: Description of input
+      placeholder: Placeholder of input
+      value: Value of input
+    validations:
+      required: true
+      is_number: true
+      regex: "[a-zA-Z0-9]+"
+  - type: dropdown
+    id: id4
+    attributes:
+      label: Label of dropdown
+      description: Description of dropdown
+      multiple: true
+      options:
+        - Option 1 of dropdown
+        - Option 2 of dropdown
+        - Option 3 of dropdown
+    validations:
+      required: true
+  - type: checkboxes
+    id: id5
+    attributes:
+      label: Label of checkboxes
+      description: Description of checkboxes
+      options:
+        - label: Option 1 of checkboxes
+          required: true
+        - label: Option 2 of checkboxes
+          required: false
+        - label: Option 3 of checkboxes
+          required: true
+`,
+				values: map[string][]string{
+					"form-field-id2":   {"Value of id2"},
+					"form-field-id3":   {"Value of id3"},
+					"form-field-id4":   {"0,1"},
+					"form-field-id5-0": {"on"},
+					"form-field-id5-2": {"on"},
+				},
+			},
+			want: `### Label of textarea
+
+` + "```bash\nValue of id2\n```" + `
+
+### Label of input
+
+Value of id3
+
+### Label of dropdown
+
+Option 1 of dropdown, Option 2 of dropdown
+
+### Label of checkboxes
+
+- [x] Option 1 of checkboxes
+- [ ] Option 2 of checkboxes
+- [x] Option 3 of checkboxes
+
+`,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			template, err := Unmarshal("test.yaml", []byte(tt.args.template))
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got := RenderToMarkdown(template, tt.args.values); got != tt.want {
+				t.Errorf("RenderToMarkdown() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_minQuotes(t *testing.T) {
+	type args struct {
+		value string
+	}
+	tests := []struct {
+		name string
+		args args
+		want string
+	}{
+		{
+			name: "without quote",
+			args: args{
+				value: "Hello\nWorld",
+			},
+			want: "```",
+		},
+		{
+			name: "with 1 quote",
+			args: args{
+				value: "Hello\nWorld\n`text`\n",
+			},
+			want: "```",
+		},
+		{
+			name: "with 3 quotes",
+			args: args{
+				value: "Hello\nWorld\n`text`\n```go\ntext\n```\n",
+			},
+			want: "````",
+		},
+		{
+			name: "with more quotes",
+			args: args{
+				value: "Hello\nWorld\n`text`\n```go\ntext\n```\n``````````bash\ntext\n``````````\n",
+			},
+			want: "```````````",
+		},
+		{
+			name: "not leading quotes",
+			args: args{
+				value: "Hello\nWorld`text````go\ntext`````````````bash\ntext``````````\n",
+			},
+			want: "```",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := minQuotes(tt.args.value); got != tt.want {
+				t.Errorf("minQuotes() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
diff --git a/modules/issue/template/unmarshal.go b/modules/issue/template/unmarshal.go
new file mode 100644
index 0000000000..e695d1e1cc
--- /dev/null
+++ b/modules/issue/template/unmarshal.go
@@ -0,0 +1,125 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package template
+
+import (
+	"fmt"
+	"io"
+	"path/filepath"
+	"strconv"
+
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/markup/markdown"
+	"code.gitea.io/gitea/modules/setting"
+	api "code.gitea.io/gitea/modules/structs"
+
+	"gopkg.in/yaml.v2"
+)
+
+// CouldBe indicates a file with the filename could be a template,
+// it is a low cost check before further processing.
+func CouldBe(filename string) bool {
+	it := &api.IssueTemplate{
+		FileName: filename,
+	}
+	return it.Type() != ""
+}
+
+// Unmarshal parses out a valid template from the content
+func Unmarshal(filename string, content []byte) (*api.IssueTemplate, error) {
+	it, err := unmarshal(filename, content)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := Validate(it); err != nil {
+		return nil, err
+	}
+
+	return it, nil
+}
+
+// UnmarshalFromEntry parses out a valid template from the blob in entry
+func UnmarshalFromEntry(entry *git.TreeEntry, dir string) (*api.IssueTemplate, error) {
+	return unmarshalFromEntry(entry, filepath.Join(dir, entry.Name()))
+}
+
+// UnmarshalFromCommit parses out a valid template from the commit
+func UnmarshalFromCommit(commit *git.Commit, filename string) (*api.IssueTemplate, error) {
+	entry, err := commit.GetTreeEntryByPath(filename)
+	if err != nil {
+		return nil, fmt.Errorf("get entry for %q: %w", filename, err)
+	}
+	return unmarshalFromEntry(entry, filename)
+}
+
+// UnmarshalFromRepo parses out a valid template from the head commit of the branch
+func UnmarshalFromRepo(repo *git.Repository, branch, filename string) (*api.IssueTemplate, error) {
+	commit, err := repo.GetBranchCommit(branch)
+	if err != nil {
+		return nil, fmt.Errorf("get commit on branch %q: %w", branch, err)
+	}
+
+	return UnmarshalFromCommit(commit, filename)
+}
+
+func unmarshalFromEntry(entry *git.TreeEntry, filename string) (*api.IssueTemplate, error) {
+	if size := entry.Blob().Size(); size > setting.UI.MaxDisplayFileSize {
+		return nil, fmt.Errorf("too large: %v > MaxDisplayFileSize", size)
+	}
+
+	r, err := entry.Blob().DataAsync()
+	if err != nil {
+		return nil, fmt.Errorf("data async: %w", err)
+	}
+	defer r.Close()
+
+	content, err := io.ReadAll(r)
+	if err != nil {
+		return nil, fmt.Errorf("read all: %w", err)
+	}
+
+	return Unmarshal(filename, content)
+}
+
+func unmarshal(filename string, content []byte) (*api.IssueTemplate, error) {
+	it := &api.IssueTemplate{
+		FileName: filename,
+	}
+
+	// Compatible with treating description as about
+	compatibleTemplate := &struct {
+		About string `yaml:"description"`
+	}{}
+
+	if typ := it.Type(); typ == api.IssueTemplateTypeMarkdown {
+		templateBody, err := markdown.ExtractMetadata(string(content), it)
+		if err != nil {
+			return nil, err
+		}
+		it.Content = templateBody
+		if it.About == "" {
+			if _, err := markdown.ExtractMetadata(string(content), compatibleTemplate); err == nil && compatibleTemplate.About != "" {
+				it.About = compatibleTemplate.About
+			}
+		}
+	} else if typ == api.IssueTemplateTypeYaml {
+		if err := yaml.Unmarshal(content, it); err != nil {
+			return nil, fmt.Errorf("yaml unmarshal: %w", err)
+		}
+		if it.About == "" {
+			if err := yaml.Unmarshal(content, compatibleTemplate); err == nil && compatibleTemplate.About != "" {
+				it.About = compatibleTemplate.About
+			}
+		}
+		for i, v := range it.Fields {
+			if v.ID == "" {
+				v.ID = strconv.Itoa(i)
+			}
+		}
+	}
+
+	return it, nil
+}
diff --git a/modules/markup/markdown/meta_test.go b/modules/markup/markdown/meta_test.go
index f525777a54..939646f8fd 100644
--- a/modules/markup/markdown/meta_test.go
+++ b/modules/markup/markdown/meta_test.go
@@ -6,6 +6,7 @@ package markdown
 
 import (
 	"fmt"
+	"strings"
 	"testing"
 
 	"code.gitea.io/gitea/modules/structs"
@@ -13,6 +14,16 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func validateMetadata(it structs.IssueTemplate) bool {
+	/*
+		A legacy to keep the unit tests working.
+		Copied from the method "func (it IssueTemplate) Valid() bool", the original method has been removed.
+		Because it becomes quite complicated to validate an issue template which is support yaml form now.
+		The new way to validate an issue template is to call the Validate in modules/issue/template,
+	*/
+	return strings.TrimSpace(it.Name) != "" && strings.TrimSpace(it.About) != ""
+}
+
 func TestExtractMetadata(t *testing.T) {
 	t.Run("ValidFrontAndBody", func(t *testing.T) {
 		var meta structs.IssueTemplate
@@ -20,7 +31,7 @@ func TestExtractMetadata(t *testing.T) {
 		assert.NoError(t, err)
 		assert.Equal(t, bodyTest, body)
 		assert.Equal(t, metaTest, meta)
-		assert.True(t, meta.Valid())
+		assert.True(t, validateMetadata(meta))
 	})
 
 	t.Run("NoFirstSeparator", func(t *testing.T) {
@@ -41,7 +52,7 @@ func TestExtractMetadata(t *testing.T) {
 		assert.NoError(t, err)
 		assert.Equal(t, "", body)
 		assert.Equal(t, metaTest, meta)
-		assert.True(t, meta.Valid())
+		assert.True(t, validateMetadata(meta))
 	})
 }
 
diff --git a/modules/structs/issue.go b/modules/structs/issue.go
index c72487fe4d..27ec81f728 100644
--- a/modules/structs/issue.go
+++ b/modules/structs/issue.go
@@ -5,7 +5,7 @@
 package structs
 
 import (
-	"strings"
+	"path/filepath"
 	"time"
 )
 
@@ -120,19 +120,57 @@ type IssueDeadline struct {
 	Deadline *time.Time `json:"due_date"`
 }
 
+// IssueFormFieldType defines issue form field type, can be "markdown", "textarea", "input", "dropdown" or "checkboxes"
+type IssueFormFieldType string
+
+const (
+	IssueFormFieldTypeMarkdown   IssueFormFieldType = "markdown"
+	IssueFormFieldTypeTextarea   IssueFormFieldType = "textarea"
+	IssueFormFieldTypeInput      IssueFormFieldType = "input"
+	IssueFormFieldTypeDropdown   IssueFormFieldType = "dropdown"
+	IssueFormFieldTypeCheckboxes IssueFormFieldType = "checkboxes"
+)
+
+// IssueFormField represents a form field
+// swagger:model
+type IssueFormField struct {
+	Type        IssueFormFieldType     `json:"type" yaml:"type"`
+	ID          string                 `json:"id" yaml:"id"`
+	Attributes  map[string]interface{} `json:"attributes" yaml:"attributes"`
+	Validations map[string]interface{} `json:"validations" yaml:"validations"`
+}
+
 // IssueTemplate represents an issue template for a repository
 // swagger:model
 type IssueTemplate struct {
-	Name     string   `json:"name" yaml:"name"`
-	Title    string   `json:"title" yaml:"title"`
-	About    string   `json:"about" yaml:"about"`
-	Labels   []string `json:"labels" yaml:"labels"`
-	Ref      string   `json:"ref" yaml:"ref"`
-	Content  string   `json:"content" yaml:"-"`
-	FileName string   `json:"file_name" yaml:"-"`
+	Name     string            `json:"name" yaml:"name"`
+	Title    string            `json:"title" yaml:"title"`
+	About    string            `json:"about" yaml:"about"` // Using "description" in a template file is compatible
+	Labels   []string          `json:"labels" yaml:"labels"`
+	Ref      string            `json:"ref" yaml:"ref"`
+	Content  string            `json:"content" yaml:"-"`
+	Fields   []*IssueFormField `json:"body" yaml:"body"`
+	FileName string            `json:"file_name" yaml:"-"`
 }
 
-// Valid checks whether an IssueTemplate is considered valid, e.g. at least name and about
-func (it IssueTemplate) Valid() bool {
-	return strings.TrimSpace(it.Name) != "" && strings.TrimSpace(it.About) != ""
+// IssueTemplateType defines issue template type
+type IssueTemplateType string
+
+const (
+	IssueTemplateTypeMarkdown IssueTemplateType = "md"
+	IssueTemplateTypeYaml     IssueTemplateType = "yaml"
+)
+
+// Type returns the type of IssueTemplate, can be "md", "yaml" or empty for known
+func (it IssueTemplate) Type() IssueTemplateType {
+	if it.Name == "config.yaml" || it.Name == "config.yml" {
+		// ignore config.yaml which is a special configuration file
+		return ""
+	}
+	if ext := filepath.Ext(it.FileName); ext == ".md" {
+		return IssueTemplateTypeMarkdown
+	} else if ext == ".yaml" || ext == ".yml" {
+		return "yaml"
+	}
+	return IssueTemplateTypeYaml
 }