compileopts, targets, main: support Wasmtime v14

Wasmtime v14 (released 2023-10-20) has a breaking change in how CLI arguments are processed.

1. Arguments after the .wasm module to run are passed to the Wasm module. The -- flag has no effect.
2. --mapdir becomes --dir, and the arguments are reversed: --dir=HOST:GUEST

compileopts/target.go

@@ -349,7 +349,7 @@ func defaultTarget(goos, goarch, triple string) (*TargetSpec, error) {
 			"--stack-first",
 			"--no-demangle",
 		)
-		spec.Emulator = "wasmtime --mapdir=/tmp::{tmpDir} {}"
+		spec.Emulator = "wasmtime --dir={tmpDir}::/tmp {}"
 		spec.ExtraFiles = append(spec.ExtraFiles,
 			"src/runtime/asm_tinygowasm.S",
 			"src/internal/task/task_asyncify_wasm.S",

main.go

@@ -797,7 +797,7 @@ func buildAndRun(pkgName string, config *compileopts.Config, stdout io.Writer, c
 			needsEnvInVars = true
 		}
 	}
-	var args, env []string
+	var args, emuArgs, env []string
 	var extraCmdEnv []string
 	if needsEnvInVars {
 		runtimeGlobals := make(map[string]string)
@@ -820,12 +820,14 @@ func buildAndRun(pkgName string, config *compileopts.Config, stdout io.Writer, c
 	} else if config.EmulatorName() == "wasmtime" {
 		// Wasmtime needs some special flags to pass environment variables
 		// and allow reading from the current directory.
-		args = append(args, "--dir=.")
+		emuArgs = append(emuArgs, "--dir=.")
 		for _, v := range environmentVars {
-			args = append(args, "--env", v)
+			emuArgs = append(emuArgs, "--env", v)
 		}
 		if len(cmdArgs) != 0 {
-			// mark end of wasmtime arguments and start of program ones: --
+			// Mark end of wasmtime arguments and start of program ones: --
+			// This should not be necessary as of Wasmtime v14:
+			// https://github.com/bytecodealliance/wasmtime/pull/6946
 			args = append(args, "--")
 			args = append(args, cmdArgs...)
 		}
@@ -876,7 +878,7 @@ func buildAndRun(pkgName string, config *compileopts.Config, stdout io.Writer, c
 			return result, err
 		}
 		name = emulator[0]
-		emuArgs := append([]string(nil), emulator[1:]...)
+		emuArgs = append(emuArgs, emulator[1:]...)
 		args = append(emuArgs, args...)
 	}
 	var cmd *exec.Cmd

targets/wasi.json

@@ -22,5 +22,5 @@
 	"extra-files": [
 		"src/runtime/asm_tinygowasm.S"
 	],
-	"emulator":      "wasmtime --mapdir=/tmp::{tmpDir} {}"
+	"emulator":      "wasmtime --dir={tmpDir}::/tmp {}"
 }