feat(cli): standard --help and --version with per-command usage

Assisted-by: Qwen 3.8 Max Preview

cmd/gasm/main.go

@@ -28,7 +28,7 @@ import (
 
 // version is the release version, stamped at build time via
 // -ldflags "-X main.version=…" (defaulting to the current release).
-var version = "0.7.0"
+var version = "0.8.0"
 
 func main() {
 	if len(os.Args) < 2 {
@@ -49,31 +49,71 @@ func main() {
 	case "lsp":
 		os.Exit(cmdLSP(os.Args[2:]))
 	case "version", "--version", "-V":
-		fmt.Printf("gasm %s\n", version)
-	case "help", "-h", "--help":
+		os.Exit(cmdVersion())
+	case "help", "--help", "-h":
 		usage(os.Stdout)
 	default:
-		fmt.Fprintf(os.Stderr, "gasm: unknown command %q\n\n", os.Args[1])
-		usage(os.Stderr)
+		fmt.Fprintf(os.Stderr, "gasm: unknown command %q — run \"gasm --help\" for usage\n", os.Args[1])
 		os.Exit(2)
 	}
 }
 
+// cmdVersion prints the release version.
+func cmdVersion() int {
+	fmt.Printf("gasm %s\n", version)
+	return 0
+}
+
 func usage(w io.Writer) {
-	fmt.Fprintf(w, `gasm %s — developer tooling for Go's Plan 9 assembler
+	fmt.Fprintf(w, `gasm %s — developer tooling for Go's Plan 9 assembler (GAsm)
+
+gasm bundles a lexer, parser, formatter, linter, standalone assembler and
+language server for Plan 9 assembly into one self-contained binary.
 
 Usage:
-  gasm tokens <file>          print the lexical token stream
-  gasm parse  <file>          parse and report syntax errors
-  gasm fmt    [-w] [path...]  canonicalise formatting (no path or a directory:
-                              reformat every .s below it in place, like go fmt)
-  gasm lint   <file...>       run static checks
-  gasm asm    [-o out.bin] <file>  assemble to machine code (amd64, Phase 2)
-  gasm lsp                    run the language server over stdio
-  gasm version                print the version
+  gasm <command> [arguments]
+  gasm [flags]
+
+Commands:
+  tokens    print the lexical token stream
+  parse     parse and report syntax errors
+  fmt       canonicalise formatting (gofmt for assembly)
+  lint      run static checks
+  asm       assemble .s files to machine code (amd64)
+  lsp       run the language server over stdio
+  version   print the version (same as --version)
+
+Flags:
+  -h, --help      show this help
+  -V, --version   print the version
+
+Run "gasm <command> -h" for a command's usage and flags.
+
+Examples:
+  gasm fmt                  reformat every .s below the current directory
+  gasm lint go-flac/*.s     run static checks over the kernels
+  gasm asm -o k.bin kern_amd64.s
 `, version)
 }
 
+// newCommand returns the FlagSet of a subcommand whose -h/--help prints a
+// proper usage block: the one-line usage, the long description and the flag
+// defaults.  The flag package routes -h/--help to fs.Usage and exits 0.
+func newCommand(name, usageLine, long string) *flag.FlagSet {
+	fs := flag.NewFlagSet(name, flag.ExitOnError)
+	fs.Usage = func() {
+		w := fs.Output()
+		fmt.Fprintf(w, "Usage: %s\n\n%s\n", usageLine, strings.TrimSpace(long))
+		hasFlags := false
+		fs.VisitAll(func(*flag.Flag) { hasFlags = true })
+		if hasFlags {
+			fmt.Fprintln(w, "\nFlags:")
+			fs.PrintDefaults()
+		}
+	}
+	return fs
+}
+
 // readSource returns the contents of path, or stdin when path is "-".
 func readSource(path string) (string, error) {
 	if path == "-" {
@@ -85,7 +125,10 @@ func readSource(path string) (string, error) {
 }
 
 func cmdTokens(args []string) int {
-	fs := flag.NewFlagSet("tokens", flag.ExitOnError)
+	fs := newCommand("tokens", "gasm tokens <file>", `
+Print the lexical token stream of FILE: position, token kind and text, one
+token per line.  FILE may be "-" to read standard input.
+`)
 	fs.Parse(args)
 	if fs.NArg() != 1 {
 		fmt.Fprintln(os.Stderr, "usage: gasm tokens <file>")
@@ -103,7 +146,11 @@ func cmdTokens(args []string) int {
 }
 
 func cmdParse(args []string) int {
-	fs := flag.NewFlagSet("parse", flag.ExitOnError)
+	fs := newCommand("parse", "gasm parse <file>", `
+Parse FILE and report syntax errors on stderr.  On success, print how many
+declarations and TEXT functions the file contains.  FILE may be "-" to read
+standard input.
+`)
 	fs.Parse(args)
 	if fs.NArg() != 1 {
 		fmt.Fprintln(os.Stderr, "usage: gasm parse <file>")
@@ -133,14 +180,24 @@ func cmdParse(args []string) int {
 }
 
 func cmdFmt(args []string) int {
-	fs_ := flag.NewFlagSet("fmt", flag.ExitOnError)
-	write := fs_.Bool("w", false, "write result to the source file")
-	fs_.Parse(args)
+	fs := newCommand("fmt", "gasm fmt [-w] [path...]", `
+Canonicalise the formatting of Plan 9 assembly sources: indentation, operand
+spacing, per-function mnemonic alignment and blank-line layout (exactly one
+blank line before each label, TEXT and GLOBL block).  Formatting is
+idempotent and preserves every line, comments included.
+
+With no paths — or a directory path — every .s file below it is reformatted
+in place and the changed files are listed, the way go fmt does; "." and "_"
+directories are skipped.  Explicit file paths print to stdout unless -w is
+given.
+`)
+	write := fs.Bool("w", false, "write result to the source file")
+	fs.Parse(args)
 	// Like go fmt: with no arguments, or with a directory argument, every .s
 	// file below the directory is formatted in place and the names of the
 	// changed files are listed; explicit file arguments keep the -w / stdout
 	// behaviour.
-	paths := fs_.Args()
+	paths := fs.Args()
 	dirMode := len(paths) == 0
 	if dirMode {
 		paths = []string{"."}
@@ -215,7 +272,16 @@ func asmFiles(dir string) ([]string, error) {
 }
 
 func cmdLint(args []string) int {
-	fs := flag.NewFlagSet("lint", flag.ExitOnError)
+	fs := newCommand("lint", "gasm lint <file...>", `
+Run the static checks over the given files and print diagnostics as
+"file:line:col: severity: message [code]".  The exit status is non-zero when
+an error-severity diagnostic is found; warnings (e.g. the register-clobber
+audit) do not affect it.
+
+Rules include unknown-instruction, operand-count, undefined-label,
+duplicate-label, missing-ret, missing-textflag-include, abi-argsize,
+unreachable-code, register-clobber and funcdata-pcdata.
+`)
 	disable := fs.String("disable", "", "comma-separated rule codes to disable")
 	fs.Parse(args)
 	if fs.NArg() == 0 {
@@ -256,7 +322,13 @@ func cmdLint(args []string) int {
 }
 
 func cmdLSP(args []string) int {
-	fs := flag.NewFlagSet("lsp", flag.ExitOnError)
+	fs := newCommand("lsp", "gasm lsp", `
+Run the language server over standard input/output: JSON-RPC 2.0 with
+Content-Length framing.  Point an LSP-capable editor at the binary and
+associate it with .s files; the target architecture is inferred from the file
+suffix (_amd64.s, _arm64.s, _riscv64.s, _loong64.s).  Provides completion,
+hover, document symbols, diagnostics and semantic-token highlighting.
+`)
 	fs.Parse(args)
 	srv := lsp.New(os.Stdin, os.Stdout)
 	if err := srv.Run(); err != nil {
@@ -267,7 +339,13 @@ func cmdLSP(args []string) int {
 }
 
 func cmdAsm(args []string) int {
-	fs := flag.NewFlagSet("asm", flag.ExitOnError)
+	fs := newCommand("asm", "gasm asm [-o out.bin] <file>", `
+Assemble FILE (amd64) without the Go toolchain: every TEXT function is
+encoded to machine code — scalar, VEX/AVX2 and EVEX/AVX-512 instructions,
+FP/SP frame mapping, local labels and file-local static symbols (GLOBL/DATA)
+resolved RIP-relative — and printed as a hex dump.  With -o the concatenated
+image (functions followed by the data section) is written to a file instead.
+`)
 	out := fs.String("o", "", "write the concatenated machine code to this file")
 	fs.Parse(args)
 	if fs.NArg() != 1 {

cmd/gasm/main_test.go

@@ -200,8 +200,24 @@ func TestCmdFmtWrite(t *testing.T) {
 func TestUsage(t *testing.T) {
 	var b bytes.Buffer
 	usage(&b)
-	if !strings.Contains(b.String(), "gasm") {
-		t.Errorf("usage text unexpected:\n%s", b.String())
+	out := b.String()
+	for _, want := range []string{
+		"gasm", "Commands:", "Flags:", "--help", "--version",
+		"tokens", "parse", "fmt", "lint", "asm", "lsp", "version",
+	} {
+		if !strings.Contains(out, want) {
+			t.Errorf("usage text missing %q:\n%s", want, out)
+		}
+	}
+}
+
+func TestCmdVersion(t *testing.T) {
+	out, _, code := capture(func() int { return cmdVersion() })
+	if code != 0 {
+		t.Fatalf("code = %d", code)
+	}
+	if !strings.Contains(out, version) {
+		t.Errorf("version output %q does not mention %q", out, version)
 	}
 }
 

justfile

@@ -3,7 +3,7 @@
 
 # gasm-devkit — developer tooling for Go's Plan 9 assembler (GAsm).
 
-version := "0.7.0"
+version := "0.8.0"
 
 default:
     @just --list