build: -pkg flag to specify package name (#150)

Allows override in the case where package name is incorrectly deduced from directory name.

Fixes #68
Fixes #147

build/cli.go

@@ -54,6 +54,7 @@ type Flags struct {
 	errout    *outputValue
 	allerrors bool
 	cpuprof   *outputValue
+	pkg       string
 	printers  []*printerValue
 }
 
@@ -69,6 +70,8 @@ func NewFlags(fs *flag.FlagSet) *Flags {
 	f.cpuprof = newOutputValue(nil)
 	fs.Var(f.cpuprof, "cpuprofile", "write cpu profile to `file`")
 
+	fs.StringVar(&f.pkg, "pkg", "", "package name (defaults to current directory name)")
+
 	goasm := newPrinterValue(printer.NewGoAsm, os.Stdout)
 	fs.Var(goasm, "out", "assembly output")
 	f.printers = append(f.printers, goasm)
@@ -83,6 +86,9 @@ func NewFlags(fs *flag.FlagSet) *Flags {
 // Config builds a configuration object based on flag values.
 func (f *Flags) Config() *Config {
 	pc := printer.NewGoRunConfig()
+	if f.pkg != "" {
+		pc.Pkg = f.pkg
+	}
 	passes := []pass.Interface{pass.Compile}
 	for _, pv := range f.printers {
 		p := pv.Build(pc)

tests/fixedbugs/issue68/asm.go

@@ -0,0 +1,18 @@
+// +build ignore
+
+package main
+
+import (
+	. "github.com/mmcloughlin/avo/build"
+	. "github.com/mmcloughlin/avo/operand"
+)
+
+func main() {
+	TEXT("Issue68", NOSPLIT, "func() uint64")
+	Doc("Issue68 tests custom package names.")
+	x := GP64()
+	MOVQ(U32(68), x)
+	Store(x, ReturnIndex(0))
+	RET()
+	Generate()
+}

tests/fixedbugs/issue68/doc.go

@@ -0,0 +1,2 @@
+// Package custom tests overriding package name with the CLI.
+package custom

tests/fixedbugs/issue68/issue68_test.go

@@ -0,0 +1,13 @@
+package custom
+
+import (
+	"testing"
+)
+
+//go:generate go run asm.go -pkg custom -out issue69.s -stubs stub.go
+
+func TestIssue68(t *testing.T) {
+	if got := Issue68(); got != 68 {
+		t.Fail()
+	}
+}

tests/fixedbugs/issue68/issue69.s

@@ -0,0 +1,9 @@
+// Code generated by command: go run asm.go -pkg custom -out issue69.s -stubs stub.go. DO NOT EDIT.
+
+#include "textflag.h"
+
+// func Issue68() uint64
+TEXT ·Issue68(SB), NOSPLIT, $0-8
+	MOVQ $0x00000044, AX
+	MOVQ AX, ret+0(FP)
+	RET

tests/fixedbugs/issue68/stub.go

@@ -0,0 +1,6 @@
+// Code generated by command: go run asm.go -pkg custom -out issue69.s -stubs stub.go. DO NOT EDIT.
+
+package custom
+
+// Issue68 tests custom package names.
+func Issue68() uint64