Modernize to Go 1.27 and split the parser

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go-version: [ '1.26.x' ]
+        go-version: [ '1.27.x' ]
     steps:
       - name: Checkout
         uses: actions/checkout@v4

CHANGELOG.md

@@ -5,6 +5,14 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Changed
+
+- Raised the minimum supported Go version to 1.27 and aligned CI with the new toolchain target
+- Adopted Go 1.21+/1.27 standard-library idioms across the codebase (`slices`, `maps`, `min`, `strings.Cut`, `errors.AsType`, range-over-int)
+- Split the monolithic parser into focused files (labels, statements, macros, operands, effective addresses) and de-duplicated the size-validation helper
+
 ## [1.3.2] - 2026-06-13
 
 ### Fixed

additional_api_test.go

@@ -134,13 +134,13 @@ func TestFileAndFormatWrappers(t *testing.T) {
 
 	elfSrc := ".org 0x1000\nstart:\n.byte 0xAA\nMOVEQ #1,D0\n"
 	for name, fn := range map[string]func() ([]byte, error){
-		"AssembleELF":                func() ([]byte, error) { return AssembleELF(strings.NewReader(elfSrc)) },
-		"AssembleBytesELF":           func() ([]byte, error) { return AssembleBytesELF([]byte(elfSrc)) },
+		"AssembleELF":      func() ([]byte, error) { return AssembleELF(strings.NewReader(elfSrc)) },
+		"AssembleBytesELF": func() ([]byte, error) { return AssembleBytesELF([]byte(elfSrc)) },
 		"AssembleBytesELFWithOptions": func() ([]byte, error) {
 			return AssembleBytesELFWithOptions([]byte(".org 0x1000\n.byte FOO\n"), opts)
 		},
-		"AssembleStringELF":       func() ([]byte, error) { return AssembleStringELF(elfSrc) },
-		"AssembleFileELF":         func() ([]byte, error) { return AssembleFileELF(writeTempSource(t, elfSrc)) },
+		"AssembleStringELF": func() ([]byte, error) { return AssembleStringELF(elfSrc) },
+		"AssembleFileELF":   func() ([]byte, error) { return AssembleFileELF(writeTempSource(t, elfSrc)) },
 		"AssembleFileELFWithOptions": func() ([]byte, error) {
 			return AssembleFileELFWithOptions(writeTempSource(t, ".org 0x1000\n.byte FOO\n"), opts)
 		},

canonical.go

@@ -196,7 +196,11 @@ func formatIndexRegister(ix instructions.EAIndex) string {
 	if ix.IsA {
 		reg = formatAddrRegister(ix.Reg)
 	}
-	out := reg + "." + map[bool]string{false: "W", true: "L"}[ix.Long]
+	width := "W"
+	if ix.Long {
+		width = "L"
+	}
+	out := reg + "." + width
 	if ix.Scale > 1 {
 		out += fmt.Sprintf("*%d", ix.Scale)
 	}

go.mod

@@ -1,3 +1,3 @@
 module github.com/jenska/m68kasm
 
-go 1.26
+go 1.27

internal/asm/asm_bench_test.go

@@ -92,7 +92,7 @@ func buildBenchmarkSource(blocks int) string {
 	sb.Grow(blocks * 64)
 
 	sb.WriteString(".org 0\n")
-	for i := 0; i < blocks; i++ {
+	for i := range blocks {
 		sb.WriteString(fmt.Sprintf("label%d: moveq #%d,d0\n", i, i%8))
 		sb.WriteString("nop\n")
 

internal/asm/assemble.go

@@ -3,6 +3,7 @@ package asm
 import (
 	"fmt"
 	"io"
+	"slices"
 
 	"github.com/jenska/m68kasm/internal/asm/instructions"
 )
@@ -169,14 +170,11 @@ func selectForm(def *instructions.InstrDef, ins *Instr, actual []instructions.Op
 	return nil, fmt.Errorf("no form matches operands/size for %s", def.Mnemonic)
 }
 
-func sizeAllowed(list []instructions.Size, sz instructions.Size) bool {
-	// Most forms allow 1-3 sizes, so linear search is efficient here
-	for _, v := range list {
-		if v == sz {
-			return true
-		}
-	}
-	return false
+// sizeAllowed reports whether sz is permitted by allowed. An empty allowed list
+// means the form places no constraint on the size. Forms allow 1-3 sizes, so a
+// linear scan is the right call here.
+func sizeAllowed(allowed []instructions.Size, sz instructions.Size) bool {
+	return len(allowed) == 0 || slices.Contains(allowed, sz)
 }
 
 func operandKinds(a *instructions.Args) []instructions.OperandKind {

internal/asm/elf.go

@@ -3,6 +3,7 @@ package asm
 import (
 	"encoding/binary"
 	"fmt"
+	"slices"
 )
 
 const (
@@ -93,9 +94,9 @@ func FormatELFWithLabels(code []byte, origin uint32, labels []DefinedLabel) []by
 		entry:         origin,
 		segmentAddr:   origin,
 		textAddr:      origin,
-		textBytes:     append([]byte(nil), code...),
+		textBytes:     slices.Clone(code),
 		textPresent:   len(code) > 0,
-		definedLabels: append([]DefinedLabel(nil), labels...),
+		definedLabels: slices.Clone(labels),
 	}
 	for i := range layout.definedLabels {
 		layout.definedLabels[i].Section = SectionText
@@ -123,7 +124,7 @@ func assembleELFLayout(p *Program) (elfLayout, error) {
 	layout := elfLayout{
 		entry:         p.Origin,
 		segmentAddr:   p.Origin,
-		definedLabels: append([]DefinedLabel(nil), p.DefinedLabels...),
+		definedLabels: slices.Clone(p.DefinedLabels),
 	}
 
 	var initializedEnd uint32 = p.Origin
@@ -436,7 +437,7 @@ func (t *elfStringTable) add(name string) uint32 {
 }
 
 func (t *elfStringTable) bytes() []byte {
-	return append([]byte(nil), t.buf...)
+	return slices.Clone(t.buf)
 }
 
 func elfStInfo(bind, typ byte) byte {

internal/asm/elf_test.go

@@ -281,7 +281,7 @@ func readSectionHeaders(t *testing.T, elf []byte) []elfSectionHeader {
 	shoff := int(binary.BigEndian.Uint32(elf[32:36]))
 	shnum := int(binary.BigEndian.Uint16(elf[48:50]))
 	headers := make([]elfSectionHeader, shnum)
-	for i := 0; i < shnum; i++ {
+	for i := range shnum {
 		base := shoff + i*sectionHeaderSize
 		headers[i] = elfSectionHeader{
 			name:      binary.BigEndian.Uint32(elf[base:]),

internal/asm/instructions/table.go

@@ -1,6 +1,9 @@
 package instructions
 
-import "sync"
+import (
+	"maps"
+	"sync"
+)
 
 // Table is a read-only lookup structure for instruction definitions.
 //
@@ -37,8 +40,6 @@ func (t *Table) Lookup(mnemonic string) *InstrDef {
 
 func cloneDefs(src map[string]*InstrDef) map[string]*InstrDef {
 	dst := make(map[string]*InstrDef, len(src))
-	for k, v := range src {
-		dst[k] = v
-	}
+	maps.Copy(dst, src)
 	return dst
 }