preprocessor: add support for code directive

A code directive is a txtar-based directive, that contains a single
file. It results in a ```-block, with the language of that block taken
from the extension of the single file in the txtar archive. The basename
of the file is irrelevant. The contents of the code directive are
formatted, unless the #nofmt tag is used.

Preprocessor-No-Write-Cache: true
Signed-off-by: Paul Jolly <[email protected]>
Change-Id: If68a9b0a10a2224e8841dfed73867fd41837b584
Dispatch-Trailer: {"type":"trybot","CL":1169683,"patchset":1,"ref":"refs/changes/83/1169683/1","targetBranch":"alpha"}

internal/cmd/preprocessor/cmd/code_node.go

@@ -0,0 +1,84 @@
+// Copyright 2023 The 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 cmd
+
+import (
+	"bytes"
+	"fmt"
+)
+
+const (
+	fnCode = "code"
+)
+
+// A codeNode is used to create a simple ```-based code block for a single file
+// whose contents are formatted. This ensures good formatting but also valid
+// code.
+type codeNode struct {
+	txtarNode
+}
+
+func (c *codeNode) nodeType() string {
+	return fnCode
+}
+
+var _ runnableNode = (*codeNode)(nil)
+
+type codeNodeRunContext struct {
+	*txtarRunContext
+}
+
+func (s *codeNode) validate() error {
+	if l := len(s.analysis.fileNames); l != 1 {
+		return fmt.Errorf("code nodes can only contain one file in the txtar archive")
+	}
+	return nil
+}
+
+func (s *codeNode) run() runnable {
+	return &codeNodeRunContext{
+		txtarRunContext: &txtarRunContext{
+			txtarNode:        s.txtarNode,
+			executionContext: s.executionContext,
+			bufferedErrorContext: &errorContextBuffer{
+				executionContext: s.executionContext,
+			},
+		},
+	}
+}
+
+func (s *codeNodeRunContext) run() (err error) {
+	defer recoverFatalError(&err)
+
+	if err := s.formatFiles(); err != nil {
+		return errorIfInError(s)
+	}
+
+	return nil
+}
+
+func (s *codeNode) writeTransformTo(b *bytes.Buffer) error {
+	p := bufPrintf(b)
+
+	// There will only be one file
+	a := s.analysis.fileNames[0]
+	f := s.effectiveArchive.Files[0]
+
+	// TODO tidy up templating etc
+	p("```%s\n", a.Language)
+	p("%s", f.Data)
+	p("```")
+	return nil
+}

internal/cmd/preprocessor/cmd/parse.go

@@ -192,6 +192,12 @@ func (rf *rootFile) parse_WithNode(n *parse.WithNode) (node, error) {
 			return nil, err
 		}
 		return &sidebysideNode{txtarNode: t}, nil
+	case fnCode:
+		t, err := rf.parse_txtarNode(n, fn.Ident, c.Args[1:])
+		if err != nil {
+			return nil, err
+		}
+		return &codeNode{txtarNode: t}, nil
 	case fnStep:
 		// Increment first because we are numbering from 1
 		rf.stepNumber++

internal/cmd/preprocessor/cmd/rootfile.go

@@ -43,6 +43,7 @@ var (
 	// were function calls.
 	templateFunctions = map[string]any{
 		fnSidebyside: true,
+		fnCode:       true,
 		fnStep:       true,
 		fnUpload:     true,
 		fnScript:     true,

internal/cmd/preprocessor/cmd/testdata/execute_transform.txtar

@@ -65,6 +65,10 @@ package site
 >
 >{{{with step}}}
 >some text
+>{{{with code "en" "x.cue example"}}}
+>-- x.cue --
+>x: 5
+>{{{end}}}
 >{{{end}}}
 >
 >Some text after
@@ -98,6 +102,9 @@ map: {
 
 {{< step stepNumber="2" >}}
 some text
+```text
+x: 5
+```
 {{< /step >}}
 
 Some text after