5 files changed, 145 insertions, 51 deletions
diff --git a/pkg/lang/vm/code/builder.go b/pkg/lang/vm/code/builder.go
index f027c49..adb2eed 100644
--- a/pkg/lang/vm/code/builder.go
+++ b/pkg/lang/vm/code/builder.go
@@ -2,14 +2,15 @@ package code
 
 import (
 	"encoding/binary"
-	"fmt"
 	"math"
 )
 
 type Builder struct {
-	code           []byte
-	debugInfo      DebugInfo
-	relativePcRefs map[int][]int
+	code      []byte
+	debugInfo DebugInfo
+
+	markers    map[Marker]int
+	markerRefs map[int]Marker
 
 	currentLine int
 	lineStart   int
@@ -17,11 +18,14 @@ type Builder struct {
 
 func NewBuilder() Builder {
 	return Builder{
-		code:           make([]byte, 0, 64),
-		debugInfo:      NewDebugInfo("unknown file"),
-		relativePcRefs: make(map[int][]int),
-		lineStart:      -1,
-		currentLine:    -1,
+		code:      make([]byte, 0, 64),
+		debugInfo: NewDebugInfo("unknown file"),
+
+		markers:    make(map[Marker]int, 0),
+		markerRefs: make(map[int]Marker, 0),
+
+		lineStart:   -1,
+		currentLine: -1,
 	}
 }
 
@@ -43,50 +47,45 @@ func (b *Builder) AppendString(s string) {
 	b.code = append(b.code, 0)
 }
 
-func (b *Builder) AppendReferenceToPc(pc int64) {
-	b.addPcRef(int(pc), b.Len())
-	b.AppendInt(pc)
+const UnfilledMarkerReference = 0x11_5AB07A6ED_600D5
+
+func (b *Builder) AppendMarkerReference(marker Marker) {
+	b.markerRefs[b.Len()] = marker
+	b.AppendInt(UnfilledMarkerReference)
 }
 
 func (b *Builder) AppendRaw(raw Raw) {
 	b.code = append(b.code, raw...)
 }
 
-func (b *Builder) AppendBuilder(other Builder) {
-	code := other.code
-	for pc, refsToPc := range other.relativePcRefs {
-		newPc := b.Len() + pc
-		for _, ref := range refsToPc {
-			valueAtRef := binary.LittleEndian.Uint64(code[ref : ref+8])
-			if int(valueAtRef) != pc {
-				panic(fmt.Errorf("reference to pc in builder does not actually reference pc. (pc: %d, value at reference: %d)", pc, valueAtRef))
+func (b *Builder) AppendBuilder(other Builder) error {
+	for marker, pc := range other.markers {
+		if parentPc, ok := b.markers[marker]; ok {
+			return ErrBuilderAppendMarkerDefinitionClash{
+				Marker:   marker,
+				ParentPc: parentPc,
+				ChildPc:  pc,
 			}
-
-			binary.LittleEndian.PutUint64(code[ref:], uint64(newPc))
-			b.addPcRef(newPc, ref+b.Len())
 		}
-	}
-
-	b.code = append(b.code, code...)
 
-	if other.debugInfo.pcToLine.Len() != 0 || other.currentLine != -1 || other.lineStart != -1 {
-		panic("appending debug infos not implemented yet")
+		b.SetMarker(marker, pc)
 	}
-}
 
-func (b *Builder) AppendBuilderWithoutAdjustingReferences(other Builder) {
-	code := other.code
-	for pc, refsToPc := range other.relativePcRefs {
-		for _, ref := range refsToPc {
-			b.addPcRef(pc, ref+b.Len())
-		}
+	for pc, marker := range other.markerRefs {
+		b.markerRefs[b.Len()+pc] = marker
 	}
 
-	b.code = append(b.code, code...)
+	b.AppendRaw(other.code)
 
-	if other.debugInfo.pcToLine.Len() != 0 || other.currentLine != -1 || other.lineStart != -1 {
-		panic("appending debug infos not implemented yet")
-	}
+	return nil
+}
+
+func (b *Builder) PutMarker(marker Marker) {
+	b.SetMarker(marker, b.Len())
+}
+
+func (b *Builder) SetMarker(marker Marker, pc int) {
+	b.markers[marker] = pc
 }
 
 func (b *Builder) StartLine(line int) {
@@ -127,18 +126,27 @@ func (b *Builder) Len() int {
 	return len(b.code)
 }
 
-func (b *Builder) Build() Code {
-	return New(b.code, b.debugInfo)
-}
+func (b *Builder) Build() (Code, error) {
+	for pc, marker := range b.markerRefs {
+		markerPc, ok := b.markers[marker]
+		if !ok {
+			return Code{}, ErrBuilderUnfulfilledMarker{
+				Marker: marker,
+				Pc:     pc,
+			}
+		}
+
+		valueAtRefPc := binary.LittleEndian.Uint64(b.code[pc : pc+8])
+		if valueAtRefPc != UnfilledMarkerReference {
+			return Code{}, ErrBuilderOverwrittenMarkerReference{
+				Marker:          marker,
+				Pc:              pc,
+				UnexpectedValue: valueAtRefPc,
+			}
+		}
 
-func (b *Builder) addPcRef(pc int, at int) {
-	refs, ok := b.relativePcRefs[pc]
-	if ok {
-		refs = append(refs, at)
-	} else {
-		refs = make([]int, 1)
-		refs[0] = at
+		b.SetInt(pc, int64(markerPc))
 	}
 
-	b.relativePcRefs[pc] = refs
+	return New(b.code, b.debugInfo), nil
 }
diff --git a/pkg/lang/vm/code/builder_test.go b/pkg/lang/vm/code/builder_test.go
new file mode 100644
index 0000000..29f1974
--- /dev/null
+++ b/pkg/lang/vm/code/builder_test.go
@@ -0,0 +1,31 @@
+package code_test
+
+import (
+	"jinx/pkg/lang/vm/code"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMarker(t *testing.T) {
+	builder := code.NewBuilder()
+
+	builder.AppendInt(123)
+	builder.AppendMarkerReference("hello world")
+
+	builder.PutMarker("hello world")
+	builder.AppendInt(123)
+
+	result, err := builder.Build()
+	assert.NoError(t, err)
+
+	expectedBuilder := code.NewBuilder()
+	expectedBuilder.AppendInt(123)
+	expectedBuilder.AppendInt(16)
+	expectedBuilder.AppendInt(123)
+
+	expected, err := expectedBuilder.Build()
+	assert.NoError(t, err)
+
+	assert.Equal(t, expected.Code(), result.Code())
+}
diff --git a/pkg/lang/vm/code/errors.go b/pkg/lang/vm/code/errors.go
new file mode 100644
index 0000000..3261dd9
--- /dev/null
+++ b/pkg/lang/vm/code/errors.go
@@ -0,0 +1,32 @@
+package code
+
+import "fmt"
+
+type ErrBuilderAppendMarkerDefinitionClash struct {
+	Marker   Marker
+	ParentPc int
+	ChildPc  int
+}
+
+func (e ErrBuilderAppendMarkerDefinitionClash) Error() string {
+	return fmt.Sprintf("parent and child builder definitions for marker '%v' clash (parent: %d, child: %d)", e.Marker, e.ParentPc, e.ChildPc)
+}
+
+type ErrBuilderUnfulfilledMarker struct {
+	Marker Marker
+	Pc     int
+}
+
+func (e ErrBuilderUnfulfilledMarker) Error() string {
+	return fmt.Sprintf("encountered unfulfilled marker '%v' at pc %d", e.Marker, e.Pc)
+}
+
+type ErrBuilderOverwrittenMarkerReference struct {
+	Marker          Marker
+	Pc              int
+	UnexpectedValue uint64
+}
+
+func (e ErrBuilderOverwrittenMarkerReference) Error() string {
+	return fmt.Sprintf("marker reference for marker '%v' at pc %d was overwritten (value: %x)", e.Marker, e.Pc, e.UnexpectedValue)
+}
diff --git a/pkg/lang/vm/code/marker.go b/pkg/lang/vm/code/marker.go
new file mode 100644
index 0000000..18b4157
--- /dev/null
+++ b/pkg/lang/vm/code/marker.go
@@ -0,0 +1,23 @@
+package code
+
+import "fmt"
+
+type Marker string
+
+func (m Marker) SubUnit(name string) Marker {
+	return Marker(fmt.Sprintf("%v:%s", m, name))
+}
+
+func (m Marker) SubMarker(format string, args ...any) Marker {
+	part := fmt.Sprintf(format, args...)
+
+	return Marker(fmt.Sprintf("%v_%s", m, part))
+}
+
+func (m Marker) String() string {
+	return string(m)
+}
+
+func (m Marker) IsEmpty() bool {
+	return string(m) == ""
+}
diff --git a/pkg/lang/vm/text/compiler.go b/pkg/lang/vm/text/compiler.go
index 21d8dae..d8b53fd 100644
--- a/pkg/lang/vm/text/compiler.go
+++ b/pkg/lang/vm/text/compiler.go
@@ -56,7 +56,7 @@ func (cpl *Compiler) Compile() (code.Code, error) {
 		return code.Code{}, err
 	}
 
-	return builder.Build(), nil
+	return builder.Build()
 }
 
 func (cpl *Compiler) compileLine() (code.Raw, error) {