v0.30.1 configuration engine as wasm

.github/workflows/test.yml

@@ -20,6 +20,9 @@ jobs:
       - run: GOOS=freebsd GOARCH=amd64 go build -o /tmp/lw-freebsd ./cmd/lw
       - run: node --test
         working-directory: internal/sink/http/web
+      # make wasm builds the engine for the page, then node runs its calls
+      - run: node --test
+        working-directory: cmd/lwconf
   # The end-to-end scripts on a host with an IPv6 loopback and playwright's
   # Chromium; the docker run needs root, so it skips
   e2e:

AGENTS.md

@@ -82,7 +82,8 @@ change touches.
 - `internal/compose` is the engine `lw --tui` and the website's WebAssembly
   share: it edits pipelines and writes the command line, environment and file
   forms, each loading back to the same pipelines; it reads no file and links
-  no TLS, HTTP or terminal code (its test runs `go list -deps`).
+  no TLS, HTTP or terminal code (its test runs `go list -deps`). `cmd/lwconf`
+  hands it to the page as WebAssembly (`make wasm`; `node --test` there).
 - `cmd/lw/cli.go` owns the command line: lw's own flags, and the commands
   table whose groups (`auth`, `tls`, `preset`, `config`) share one flag
   mechanism; `config.Load` takes the parsed `config.Args`. Presets are rows of

Makefile

@@ -69,7 +69,7 @@ DEB_MAINTAINER ?= Maintainer <maintainer@example.org>
 
 .DEFAULT_GOAL := help
 
-.PHONY: help check-go build release dev test verify e2e image image-check install uninstall deb arch completion clean version
+.PHONY: help check-go build release dev wasm test verify e2e image image-check install uninstall deb arch completion clean version
 
 help:
 	@echo "Usage: make <target> [VARIABLE=value ...]"
@@ -78,12 +78,14 @@ help:
 	@echo "  build        Build $(BIN_DIR)/$(BINARY) with version metadata"
 	@echo "  release      Build it static, stripped and trimmed (CGO_ENABLED=0)"
 	@echo "  dev          Build it with the race detector"
+	@echo "  wasm         Build $(BIN_DIR)/lwconf.wasm, the engine for the website, beside its"
+	@echo "               loader wasm_exec.js, and print both checksums"
 	@echo "  version      Print the version metadata a build embeds"
 	@echo "  completion   Regenerate $(PKG_DIR)/completion from lw's command tables"
 	@echo "  clean        Remove $(BIN_DIR)/"
 	@echo "Check:"
 	@echo "  test         Run the Go tests"
-	@echo "  verify       vet, gofmt, tests, linux and freebsd cross builds, web client tests"
+	@echo "  verify       vet, gofmt, tests, linux, freebsd and wasm cross builds, node tests"
 	@echo "  e2e          Build, then run each of $(E2E) with --auto and report"
 	@echo "Container:"
 	@echo "  image        Build $(IMAGE):$(IMAGE_TAG) with $(CONTAINER_ENGINE) (scratch, static, UID 65532)"
@@ -120,6 +122,13 @@ release: check-go
 dev: check-go
 	$(GO) build -race $(GO_BUILDFLAGS) -ldflags "$(VERSION_LDFLAGS) $(GO_LDFLAGS)" -o $(BIN_DIR)/$(BINARY) $(SRC)
 
+# The page loads the toolchain's own loader, which uses no eval: its CSP needs
+# only 'wasm-unsafe-eval'
+wasm: check-go
+	GOOS=js GOARCH=wasm $(GO) build -trimpath $(GO_BUILDFLAGS) -ldflags "-s -w $(VERSION_LDFLAGS) $(GO_LDFLAGS)" -o $(BIN_DIR)/lwconf.wasm ./cmd/lwconf
+	install -m 0644 "$$($(GO) env GOROOT)/lib/wasm/wasm_exec.js" $(BIN_DIR)/wasm_exec.js
+	@cd $(BIN_DIR) && { sha256sum lwconf.wasm wasm_exec.js 2>/dev/null || sha256 -r lwconf.wasm wasm_exec.js; }
+
 test: check-go
 	$(GO) test ./...
 
@@ -146,10 +155,11 @@ verify: test
 		echo "cross build $$target"; \
 		CGO_ENABLED=0 GOOS=$${target%/*} GOARCH=$${target#*/} $(GO) build -o /dev/null $(SRC) || exit 1; \
 	done
+	@echo "cross build js/wasm"; GOOS=js GOARCH=wasm $(GO) build -o /dev/null ./cmd/lwconf
 	@if command -v node >/dev/null 2>&1; then \
-		cd $(WEB_DIR) && node --test; \
+		(cd $(WEB_DIR) && node --test) && cd cmd/lwconf && node --test; \
 	else \
-		echo "node not found: web client tests skipped"; \
+		echo "node not found: web client and lwconf tests skipped"; \
 	fi
 
 # A script exits 0 (passed), 77 (skipped: the host lacks what it tests) or

cmd/lwconf/lwconf.test.mjs

@@ -0,0 +1,64 @@
+import { after, test } from "node:test";
+import assert from "node:assert/strict";
+import { execFileSync } from "node:child_process";
+import { createHash } from "node:crypto";
+import { mkdtempSync, readFileSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { pathToFileURL } from "node:url";
+
+// Built by make wasm and started as the page starts it: the toolchain's loader
+// beside the module, main running until the page closes. The make run is its
+// own: a parent GNU make's flags would stop a BSD one.
+const dir = mkdtempSync(join(tmpdir(), "lwconf-"));
+after(() => rmSync(dir, { recursive: true, force: true }));
+const made = execFileSync("make", ["-s", "wasm", `BIN_DIR=${dir}`, "VERSION=v0.0.0-node"], {
+  cwd: join(import.meta.dirname, "../.."), encoding: "utf8",
+  env: { ...process.env, MAKEFLAGS: "", MFLAGS: "", MAKELEVEL: "" },
+});
+await import(pathToFileURL(join(dir, "wasm_exec.js")));
+const go = new globalThis.Go();
+const { instance } = await WebAssembly.instantiate(readFileSync(join(dir, "lwconf.wasm")), go.importObject);
+go.run(instance);
+const call = (name, ...args) => JSON.parse(globalThis.lwconf[name](...args));
+
+test("make wasm stamps the version and prints both checksums", () => {
+  for (const file of ["lwconf.wasm", "wasm_exec.js"]) {
+    const sum = createHash("sha256").update(readFileSync(join(dir, file))).digest("hex");
+    assert.match(made, new RegExp(`^${sum} +${file.replace(".", "\\.")}$`, "m"));
+  }
+  assert.equal(call("schema").value.version, "v0.0.0-node");
+});
+
+// Off the host a directory path ends in '/'
+test("a preset's pipelines, written as a command line, parse and validate back to themselves", () => {
+  const { value: pipelines } = call("preset", "tail", JSON.stringify({ path: "/var/log/" }));
+  assert.equal(pipelines[0].plugin_sources[0].config.directory, "/var/log/");
+  const { value: line } = call("emit", JSON.stringify(pipelines), "command");
+  assert.match(line, /^lw \\\n {2}--pipeline tail/);
+  assert.deepEqual(call("parse", line).value, pipelines);
+  assert.deepEqual(call("validate", JSON.stringify(pipelines)).value, pipelines);
+  assert.match(call("emit", JSON.stringify(pipelines), "file").value, /^\[\[pipelines\]\]/m);
+});
+
+test("a refused call answers why, and the engine keeps answering", () => {
+  const refused = [
+    [["parse", "lw --nope x"], /not a pipeline flag/],
+    [["parse", "lw"], /no pipeline flags/],
+    [["parse"], /^usage: lwconf\.parse\(line\)/],
+    [["parse", 5], /^usage: /],
+    [["preset", "tail", JSON.stringify({ path: "/var/log" })], /path/],
+    [["validate", JSON.stringify([{ name: "p" }])], /no sources/],
+    [["validate", JSON.stringify(["a", "b"].map((name, i) => ({
+      name, plugin_sources: [{ type: "tcp_chain", config: { port: [9000, "x"][i] } }], plugin_sinks: [{ type: "null" }],
+    })))], /^pipelines\[1\]\.plugin_sources\[tcp_chain\]\.config\.port: not an integer$/],
+    [["emit", JSON.stringify([{ name: "p" }]), "command"], /no sources/],
+    [["emit", "[]", "yaml"], /no form "yaml"/],
+  ];
+  for (const [args, want] of refused) {
+    const got = call(...args);
+    assert.equal(got.value, undefined, `${args}`);
+    assert.match(got.error, want, `${args}`);
+  }
+  assert.ok(call("schema").value.sources.length > 0);
+});

cmd/lwconf/main.go

@@ -0,0 +1,90 @@
+//go:build js && wasm
+
+// Command lwconf is the configuration engine as WebAssembly, for the website.
+// It sets globalThis.lwconf, whose calls take strings and return a JSON object:
+// {"value": ...}, or {"error": "..."} for a call refused. Pipelines travel in
+// compose's JSON form; off the host a preset's directory path ends in '/'.
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"slices"
+	"strings"
+	"syscall/js"
+
+	"github.com/lixenwraith/logwisp/internal/compose"
+)
+
+// calls are lwconf's, by name, with the string arguments each takes
+var calls = map[string]struct {
+	args []string
+	call func(args []string) (any, error)
+}{
+	"schema": {nil, func([]string) (any, error) { return compose.NewSchema(), nil }},
+	"preset": {[]string{"name", "values"}, func(a []string) (any, error) {
+		var values map[string]string
+		if err := json.Unmarshal([]byte(a[1]), &values); err != nil {
+			return nil, fmt.Errorf("values: %w", err)
+		}
+		return pipelines(compose.FromPreset(a[0], values, nil))
+	}},
+	"parse": {[]string{"line"}, func(a []string) (any, error) {
+		return pipelines(compose.FromCommandLine(a[0], nil))
+	}},
+	"validate": {[]string{"pipelines"}, func(a []string) (any, error) {
+		c, err := compose.FromJSON([]byte(a[0]))
+		if err == nil {
+			err = c.Validate()
+		}
+		return pipelines(c, err)
+	}},
+	"emit": {[]string{"pipelines", "form"}, func(a []string) (any, error) {
+		c, err := compose.FromJSON([]byte(a[0]))
+		if err != nil {
+			return nil, err
+		}
+		forms := compose.Forms()
+		if i := slices.IndexFunc(forms, func(f compose.Form) bool { return f.Name == a[1] }); i >= 0 {
+			return forms[i].Write(c)
+		}
+		return nil, fmt.Errorf("no form %q", a[1])
+	}},
+}
+
+// pipelines is a composition's value: its pipelines settled, ids given
+func pipelines(c *compose.Composition, err error) (any, error) {
+	if err != nil {
+		return nil, err
+	}
+	data, err := c.JSON()
+	return json.RawMessage(data), err
+}
+
+func main() {
+	api := map[string]any{}
+	for name := range calls {
+		api[name] = js.FuncOf(func(_ js.Value, args []js.Value) any { return answer(name, args) })
+	}
+	js.Global().Set("lwconf", js.ValueOf(api))
+	select {} // the page calls in until it closes
+}
+
+// answer is a call's JSON for the page: its value, or why it was refused
+func answer(name string, args []js.Value) string {
+	c := calls[name]
+	value, err := any(nil), fmt.Errorf("usage: lwconf.%s(%s), each a string", name, strings.Join(c.args, ", "))
+	if len(args) == len(c.args) && !slices.ContainsFunc(args, func(v js.Value) bool { return v.Type() != js.TypeString }) {
+		strs := make([]string, len(args))
+		for i, arg := range args {
+			strs[i] = arg.String()
+		}
+		value, err = c.call(strs)
+	}
+	out := map[string]any{"value": value}
+	if err != nil {
+		out = map[string]any{"error": err.Error()}
+	}
+	data, _ := json.Marshal(out)
+	return string(data)
+}

doc/installation.md

@@ -26,6 +26,9 @@ The Makefile works with GNU make and BSD make alike. Targets:
   - `make build`: `bin/lw`, with version, commit and build time from git
   - `make release`: the same, static (`CGO_ENABLED=0`), `-trimpath`, stripped
   - `make dev`: built with the race detector
+  - `make wasm`: `bin/lwconf.wasm`, the configuration engine for the
+    website, version stamped, beside the toolchain's `wasm_exec.js`; prints
+    both checksums
   - `make version`: the metadata a build would embed
   - `make completion`: regenerate the bash, zsh and fish completion in
     `deploy/package/completion/` from `cmd/lw`'s `shorts` and `commands`
@@ -34,8 +37,9 @@ The Makefile works with GNU make and BSD make alike. Targets:
 - Check
   - `make test`: the Go tests
   - `make verify`: tests, `go vet`, `gofmt -l` on the Go files changed since
-    `main`, linux and freebsd cross builds for amd64 and arm64, and the web
-    client's `node --test` when node is installed
+    `main`, linux and freebsd cross builds for amd64 and arm64 and the js/wasm
+    one, and, when node is installed, `node --test` for the web client and
+    for `cmd/lwconf` (which runs `make wasm`)
   - `make e2e`: builds, then runs every `test/*-test.sh --auto` in turn and
     reports passes, failures and skips; `E2E='test/scram-*-test.sh'` runs a
     subset; see [Test Scripts](#test-scripts)

doc/todo.md

@@ -114,14 +114,21 @@ Steps:
    optional, in `color`: export the 16 xterm reference shades (RGBTo16 maps
    the site's hues badly, so the 16-color tier is chosen by hand).
 5. `lw --tui`: done ([doc/cli.md](cli.md#lw---tui)).
-6. WebAssembly: `cmd/lwconf` (`js && wasm`) exposes schema, preset, parse,
-   validate and emit to the page as JSON strings. `make wasm` builds
-   `bin/lwconf.wasm` with the version stamped, copies the toolchain's
-   `wasm_exec.js`, and prints both checksums. A prototype measured about 6 MB,
-   1.7 MB gzipped, ready in about 60 ms in Chromium; `wasm_exec.js` uses no
-   eval, so the page needs only `'wasm-unsafe-eval'` in its `script-src`.
+6. WebAssembly: done. `make wasm` builds `bin/lwconf.wasm`, version stamped,
+   beside the toolchain's `wasm_exec.js`, and prints both checksums: about
+   6.9 MB, 1.9 MB gzipped. `wasm_exec.js` uses no eval, so the page needs only
+   `'wasm-unsafe-eval'` in its `script-src`. The page runs the module with
+   `new Go().run(instance)`, then calls `globalThis.lwconf`; each call takes
+   strings and returns a JSON object, `{"value": ...}` or `{"error": "..."}`:
+   - `schema()`: what `lw --schema` prints.
+   - `preset(name, values)`: a preset's pipelines; `values` is a JSON object
+     of strings, and a directory path ends in `/`.
+   - `parse(line)`: a pasted command line's pipelines.
+   - `validate(pipelines)`: the pipelines settled (defaults, kinds, ids), or
+     the first problem by its key path.
+   - `emit(pipelines, form)`: `command`, `environment` or `file`.
+   - Pipelines are a JSON list in the file's shape (`name`, `flow`,
+     `plugin_sources`, `plugin_sinks`); a misspelled key is refused.
 
-Verify:
-- CI builds `cmd/lwconf` for `GOOS=js` and runs a node test of its calls.
-- The diagram rendered into a cell buffer at 80x24 and 64x24, per tier; a
-  scripted session on a pseudo-terminal for Run and each output.
+Still to verify: a scripted session on a pseudo-terminal for Run and each
+output.

internal/compose/compose.go

@@ -5,6 +5,7 @@
 package compose
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 	"reflect"
@@ -59,7 +60,8 @@ func FromPreset(name string, values map[string]string, isDir config.IsDir) (*Com
 }
 
 // FromCommandLine starts from a pasted lw command line, quoted as a POSIX
-// shell reads it; it takes pipeline flags only, as a composition holds no settings
+// shell reads it; it takes pipeline flags only, at least one, as a composition
+// holds no settings
 func FromCommandLine(line string, isDir config.IsDir) (*Composition, error) {
 	words, err := split(strings.NewReplacer("\r\n", "\n", "\r", "\n").Replace(line)) // pasted line ends
 	if err != nil {
@@ -86,6 +88,9 @@ func FromCommandLine(line string, isDir config.IsDir) (*Composition, error) {
 		}
 		specs = append(specs, config.Spec{Flag: flag, Value: value})
 	}
+	if len(specs) == 0 {
+		return nil, errors.New("no pipeline flags")
+	}
 	pipelines, err := config.SpecPipelines(specs, isDir)
 	if err != nil {
 		return nil, err
@@ -117,13 +122,13 @@ func (c *Composition) settle() error {
 		for j, s := range p.PluginSources {
 			p.PluginSources[j].Config = orEmpty(s.Config)
 			if err := config.Coerce("source", s.Type, p.PluginSources[j].Config); err != nil {
-				return fmt.Errorf("source %s: %w", s.ID, err)
+				return config.At(fmt.Sprintf("pipelines[%d].plugin_sources[%s].config", i, s.ID), err)
 			}
 		}
 		for j, s := range p.PluginSinks {
 			p.PluginSinks[j].Config = orEmpty(s.Config)
 			if err := config.Coerce("sink", s.Type, p.PluginSinks[j].Config); err != nil {
-				return fmt.Errorf("sink %s: %w", s.ID, err)
+				return config.At(fmt.Sprintf("pipelines[%d].plugin_sinks[%s].config", i, s.ID), err)
 			}
 		}
 	}
@@ -477,6 +482,75 @@ func (c *Composition) File() ([]byte, error) {
 	return toml.Marshal(map[string]any{"pipelines": c.Pipelines})
 }
 
+// Form is a way to write a composition, named for what it is: each loads back
+// to the same pipelines
+type Form struct {
+	Name, Hint string
+	Write      func(*Composition) (string, error)
+}
+
+var forms = []Form{
+	{"command", "lw's flags", (*Composition).CommandLine},
+	{"environment", "LOGWISP_ variables: one pipeline", (*Composition).Environment},
+	{"file", "a configuration file's pipelines", func(c *Composition) (string, error) {
+		data, err := c.File()
+		return string(data), err
+	}},
+}
+
+// Forms are what a composition writes: lw --tui prints one, the website shows them
+func Forms() []Form { return slices.Clone(forms) }
+
+// FromJSON starts from pipelines as the website keeps them: a JSON list of
+// tables in a file's shape, a misspelled key refused as a file's is, a null
+// a value left unset
+func FromJSON(data []byte) (*Composition, error) {
+	var tables any
+	if err := json.Unmarshal(data, &tables); err != nil {
+		return nil, err
+	}
+	cfg := &config.Config{}
+	if err := config.Scan(map[string]any{"pipelines": dropNulls(tables)}, cfg); err != nil {
+		return nil, err
+	}
+	return FromConfig(cfg)
+}
+
+// dropNulls removes JSON's nulls from tables and lists, which the shell forms
+// would write as text
+func dropNulls(v any) any {
+	switch v := v.(type) {
+	case map[string]any:
+		for k, e := range v {
+			if e == nil {
+				delete(v, k)
+			} else {
+				v[k] = dropNulls(e)
+			}
+		}
+	case []any:
+		v = slices.DeleteFunc(v, func(e any) bool { return e == nil })
+		for i, e := range v {
+			v[i] = dropNulls(e)
+		}
+		return v
+	}
+	return v
+}
+
+// JSON writes the pipelines as FromJSON reads them, keyed as File writes them
+func (c *Composition) JSON() ([]byte, error) {
+	data, err := toml.Marshal(map[string]any{"pipelines": c.Pipelines})
+	if err != nil {
+		return nil, err
+	}
+	root, err := toml.NewParser(data).Parse()
+	if err != nil {
+		return nil, err
+	}
+	return json.Marshal(root["pipelines"])
+}
+
 // quote leaves a word of these characters bare, and single-quotes any other,
 // or one starting with '=', which zsh expands
 func quote(word string) string {

internal/compose/compose_test.go

@@ -34,10 +34,11 @@ func TestEngineLinksNoHostCode(t *testing.T) {
 	}
 }
 
-// A pasted command line, its line ends LF or CRLF, starts the composition that
-// wrote it: escaped and quoted values, nested keys, lists, moved filters,
-// stages whose flags' defaults differ from a file's, a value starting with '-'
-func TestPastedCommandLineStartsTheSameComposition(t *testing.T) {
+// A pasted command line, its line ends LF or CRLF, and the website's JSON each
+// start the composition that wrote them: escaped and quoted values, nested
+// keys, lists, moved filters, stages whose flags' defaults differ from a
+// file's, a value starting with '-', JSON's numbers for integers
+func TestWrittenFormsStartTheSameComposition(t *testing.T) {
 	c := &Composition{}
 	must := func(err error) {
 		t.Helper()
@@ -80,6 +81,36 @@ func TestPastedCommandLineStartsTheSameComposition(t *testing.T) {
 			t.Fatalf("%q\n got %+v %v\nwant %+v", pasted, got, err, c)
 		}
 	}
+	data, err := c.JSON()
+	must(err)
+	if got, err := FromJSON(data); err != nil || !reflect.DeepEqual(got, c) {
+		t.Fatalf("%s\n got %+v %v\nwant %+v", data, got, err, c)
+	}
+}
+
+// A null in the website's JSON is a value left unset, which every form then
+// leaves out, in a table or a list
+func TestANullInJSONIsUnset(t *testing.T) {
+	with, err := FromJSON([]byte(`[{"name":"p","flow":{"rate_limit":null,"filters":[{"patterns":["a",null]}]},
+		"plugin_sources":[{"type":"file","config":{"directory":"/x/","pattern":null}}],
+		"plugin_sinks":[{"type":"console","config":{"color":null}}]}]`))
+	if err != nil {
+		t.Fatal(err)
+	}
+	without, err := FromJSON([]byte(`[{"name":"p","flow":{"filters":[{"patterns":["a"]}]},
+		"plugin_sources":[{"type":"file","config":{"directory":"/x/"}}],"plugin_sinks":[{"type":"console"}]}]`))
+	if err != nil || !reflect.DeepEqual(with, without) {
+		t.Fatalf("%v\n got %+v\nwant %+v", err, with, without)
+	}
+}
+
+// The website's JSON refuses a misspelled key as a file does, at any depth
+func TestAMisspelledJSONKeyIsRefused(t *testing.T) {
+	for _, data := range []string{`[{"name":"p","plugin_source":[]}]`, `[{"name":"p","flow":{"rate_limt":{}}}]`} {
+		if _, err := FromJSON([]byte(data)); err == nil || !strings.Contains(err.Error(), "unknown key") {
+			t.Errorf("%s: %v", data, err)
+		}
+	}
 }
 
 // The command line and environment carry no control character, which a

internal/config/config.go

@@ -133,7 +133,7 @@ const (
 type FilterConfig struct {
 	Type     FilterType  `toml:"type" default:"include" lw:"enum=include|exclude" help:"pass only matching entries, or drop them"`
 	Logic    FilterLogic `toml:"logic" default:"or" lw:"enum=or|and" help:"match any pattern, or all"`
-	Patterns []string    `toml:"patterns" lw:"hint=regex" help:"RE2 patterns"`
+	Patterns []string    `toml:"patterns,omitempty" lw:"hint=regex" help:"RE2 patterns"`
 }
 
 // --- Sources ---

internal/config/validate.go

@@ -90,7 +90,7 @@ func ValidatePipelines(pipelines []PipelineConfig) error {
 				single[role+typ] = p.Name
 			}
 			if _, err := decode(role, typ, m); err != nil {
-				return at(path+".config", err)
+				return At(path+".config", err)
 			}
 			return nil
 		}
@@ -130,14 +130,14 @@ func checkFlow(f *FlowConfig, path string) error {
 	}
 	for _, key := range slices.Sorted(maps.Keys(stages)) {
 		if err := Settle(stages[key]); err != nil {
-			return at(path+"."+key, err)
+			return At(path+"."+key, err)
 		}
 	}
 	return nil
 }
 
-// at prefixes err with the path of the table it was found in
-func at(path string, err error) error {
+// At prefixes err with the path of the table it was found in
+func At(path string, err error) error {
 	if ke, ok := errors.AsType[*KeyError](err); ok {
 		return fmt.Errorf("%s.%s: %w", path, ke.Key, ke.Err)
 	}

internal/tui/dialog.go

@@ -240,29 +240,16 @@ func (f *presetForm) apply(a *app) {
 	a.use(c.Pipelines[0])
 }
 
-// outputs are what o offers: run, or print one form
-var outputs = []struct {
-	name, hint string
-	form       func(*compose.Composition) (string, error) // nil runs
-}{
-	{"run", "start the pipelines now, with lw's other settings", nil},
-	{"command line", "print lw's flags", (*compose.Composition).CommandLine},
-	{"environment", "print LOGWISP_ variables: one pipeline", (*compose.Composition).Environment},
-	{"file", "print a configuration file's pipelines", func(c *compose.Composition) (string, error) {
-		data, err := c.File()
-		return string(data), err
-	}},
-}
-
+// outputMenu is what o offers: run, or print one of the forms
 func (a *app) outputMenu() dialog {
-	var options []ui.Option
-	for _, o := range outputs {
-		options = append(options, ui.Option{Name: o.name, Hint: o.hint})
+	forms := compose.Forms()
+	options := []ui.Option{{Name: "run", Hint: "start the pipelines now, with lw's other settings"}}
+	for _, f := range forms {
+		options = append(options, ui.Option{Name: f.Name, Hint: "print " + f.Hint})
 	}
 	return &chooser{title: "Output, once the screen closes", list: ui.NewOptionListState(options),
 		pick: func(a *app, i int) {
-			o := outputs[i]
-			if o.form == nil {
+			if i == 0 {
 				if a.problem != nil {
 					a.status = "not valid yet: c shows the problem"
 					return
@@ -270,7 +257,7 @@ func (a *app) outputMenu() dialog {
 				a.result, a.done = Result{Exit: Start, Pipelines: a.comp.Pipelines}, true
 				return
 			}
-			text, err := o.form(a.comp)
+			text, err := forms[i-1].Write(a.comp)
 			if err != nil {
 				a.status = err.Error()
 				return

internal/tui/tui.go

@@ -311,9 +311,6 @@ func slicesHasKey(keys []config.Key, name string) bool {
 // paste starts over from a pasted command line
 func (a *app) paste(text string) {
 	c, err := compose.FromCommandLine(text, config.HostIsDir)
-	if err == nil && len(c.Pipelines) == 0 {
-		err = errors.New("no pipeline flags")
-	}
 	if err != nil {
 		a.status = "paste: " + err.Error()
 		return