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|
// gonix eval — evaluate a Nix expression using the WASM evaluator.
//
// Usage:
//
// eval <path-to-libnixexpr.wasm> <nix-expression>
//
// Example:
//
// eval ./build-wasm/lix/libnixexpr.wasm 'builtins.nixVersion'
package main
import (
"context"
"fmt"
"os"
"strings"
"time"
"github.com/nixos/lix/gonix/store"
"github.com/nixos/lix/gonix/wasm"
)
func main() {
// Default to the native compiler (wazevo); --interpreted opts out for debugging.
args := os.Args[1:]
compiled := true
for i := 0; i < len(args); i++ {
if args[i] == "--interpreted" {
compiled = false
args = append(args[:i], args[i+1:]...)
break
}
}
if len(args) < 2 {
fmt.Fprintf(os.Stderr, "usage: %s [--interpreted] <libnixexpr.wasm> <expr>\n", os.Args[0])
os.Exit(1)
}
wasmPath := args[0]
expr := args[1]
t0 := time.Now()
wasmBytes, err := os.ReadFile(wasmPath)
if err != nil {
fmt.Fprintf(os.Stderr, "read wasm: %v\n", err)
os.Exit(1)
}
ctx := context.Background()
s := &store.StubStore{}
rt, err := wasm.New(ctx, wasmBytes, s, "", compiled)
if err != nil {
fmt.Fprintf(os.Stderr, "create runtime: %v\n", err)
os.Exit(1)
}
defer rt.Close(ctx)
fmt.Fprintf(os.Stderr, "[timing] total startup: %s\n", time.Since(t0).Round(time.Millisecond))
t1 := time.Now()
if err := rt.Init(ctx, "/nix/store"); err != nil {
fmt.Fprintf(os.Stderr, "nix_init: %v\n", err)
os.Exit(1)
}
fmt.Fprintf(os.Stderr, "[timing] nix_init: %s\n", time.Since(t1).Round(time.Millisecond))
t2 := time.Now()
handle, err := rt.EvalExpr(ctx, expr)
fmt.Fprintf(os.Stderr, "[timing] eval: %s\n", time.Since(t2).Round(time.Millisecond))
if err != nil {
fmt.Fprintf(os.Stderr, "eval: %v\n", err)
os.Exit(1)
}
defer rt.FreeValue(ctx, handle)
t3 := time.Now()
result, err := printValue(ctx, rt, handle, make(map[uint32]bool))
fmt.Fprintf(os.Stderr, "[timing] print: %s\n", time.Since(t3).Round(time.Millisecond))
if err != nil {
fmt.Fprintf(os.Stderr, "print: %v\n", err)
os.Exit(1)
}
fmt.Println(result)
c := &rt.Counters
fmt.Fprintf(os.Stderr, "[counters] invoke: %d (host=%d wasm=%d) cxa: %d (throw=%d) store: %d syscall: %d other: %d\n",
c.InvokeTotal.Load(), c.InvokeHost.Load(), c.InvokeWasm.Load(),
c.CxaTotal.Load(), c.CxaThrow.Load(),
c.Store.Load(), c.Syscall.Load(), c.Other.Load())
}
// ValueType enum from eval.hh:
// nThunk=0 nInt=1 nFloat=2 nBool=3 nString=4 nPath=5 nNull=6 nAttrs=7 nList=8 nFunction=9 nExternal=10
// printValue pretty-prints a Nix value handle.
//
// seen tracks the WASM pointer identity of every attrs/list value entered so
// far, mirroring cppnix's ValuesSeen set in print.cc. When a value's pointer
// is already in seen, we print «repeated» instead of recursing — this is the
// correct way to handle Nix's self-referential derivation attrsets (the `all`
// attribute forms a cycle: the output attrset contains `all = [ <itself> ]`).
func printValue(ctx context.Context, rt *wasm.Runtime, handle int32, seen map[uint32]bool) (string, error) {
if err := rt.ForceValue(ctx, handle); err != nil {
return "", err
}
vtype, err := rt.ValueType(ctx, handle)
if err != nil {
return "", err
}
switch vtype {
case 1: // nInt
n, err := rt.GetInt(ctx, handle)
if err != nil {
return "", err
}
return fmt.Sprintf("%d", n), nil
case 2: // nFloat
f, err := rt.GetFloat(ctx, handle)
if err != nil {
return "", err
}
return fmt.Sprintf("%g", f), nil
case 3: // nBool
b, err := rt.GetBool(ctx, handle)
if err != nil {
return "", err
}
if b {
return "true", nil
}
return "false", nil
case 4: // nString
s, err := rt.GetString(ctx, handle)
if err != nil {
return "", err
}
return fmt.Sprintf("%q", s), nil
case 5: // nPath
s, err := rt.GetString(ctx, handle)
if err != nil {
return "", err
}
return s, nil
case 6: // nNull
return "null", nil
case 7: // nAttrs
ptr, err := rt.ValuePtr(ctx, handle)
if err != nil {
return "", err
}
if ptr != 0 && seen[ptr] {
return "«repeated»", nil
}
if ptr != 0 {
seen[ptr] = true
}
namesRaw, err := rt.GetAttrNames(ctx, handle)
if err != nil {
return "", err
}
names := strings.Fields(namesRaw)
if len(names) == 0 {
return "{ }", nil
}
var sb strings.Builder
sb.WriteString("{ ")
for _, name := range names {
attr, err := rt.GetAttr(ctx, handle, name)
if err != nil {
return "", fmt.Errorf("attr %q: %w", name, err)
}
val, err := printValue(ctx, rt, attr, seen)
rt.FreeValue(ctx, attr)
if err != nil {
return "", fmt.Errorf("attr %q: %w", name, err)
}
sb.WriteString(name)
sb.WriteString(" = ")
sb.WriteString(val)
sb.WriteString("; ")
}
sb.WriteString("}")
return sb.String(), nil
case 8: // nList
ptr, err := rt.ValuePtr(ctx, handle)
if err != nil {
return "", err
}
if ptr != 0 && seen[ptr] {
return "«repeated»", nil
}
if ptr != 0 {
seen[ptr] = true
}
n, err := rt.ListLength(ctx, handle)
if err != nil {
return "", err
}
if n == 0 {
return "[ ]", nil
}
var sb strings.Builder
sb.WriteString("[ ")
for i := int32(0); i < n; i++ {
elem, err := rt.ListGet(ctx, handle, i)
if err != nil {
return "", fmt.Errorf("list[%d]: %w", i, err)
}
val, err := printValue(ctx, rt, elem, seen)
rt.FreeValue(ctx, elem)
if err != nil {
return "", fmt.Errorf("list[%d]: %w", i, err)
}
sb.WriteString(val)
sb.WriteString(" ")
}
sb.WriteString("]")
return sb.String(), nil
case 9: // nFunction
return "<LAMBDA>", nil
default:
return fmt.Sprintf("<value type=%d>", vtype), nil
}
}
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