func (in *Input) enabled() bool {
	return len(in.ifdefStack) == 0 || in.ifdefStack[len(in.ifdefStack)-1]
}

func (in *Input) expectNewline(directive string) {
	tok := in.Stack.Next()
	if tok != '\n' {
		in.expectText("expected newline after", directive)
	}
}

func (in *Input) Next() ScanToken {
	if in.peek {
		in.peek = false
		tok := in.peekToken
		in.text = in.peekText
		return tok
	}

	}
	return name, abi, true
}

// registerIndirect parses the general form of a register indirection.
// It can be (R1), (R2*scale), (R1)(R2*scale), (R1)(R2.SXTX<<3) or (R1)(R2<<3)
// where R1 may be a simple register or register pair R:R or (R, R) or (R+R).
// Or it might be a pseudo-indirection like (FP).
// We are sitting on the opening parenthesis.
func (p *Parser) registerIndirect(a *obj.Addr, prefix rune) {

CFLAGS, CPPFLAGS, CXXFLAGS, FFLAGS and LDFLAGS may be defined with pseudo
#cgo directives within these comments to tweak the behavior of the C, C++
or Fortran compiler. Values defined in multiple directives are concatenated
together. The directive can include a list of build constraints limiting its
effect to systems satisfying one of the constraints
(see https://golang.org/pkg/go/build/#hdr-Build_Constraints for details about the constraint syntax).
For example:

		File: []ZipTestFile{
			{
				Name:    "世界",
				Content: []byte{},
				Mode:    0644,
				// Name is valid UTF-8, but format does not have UTF-8 flag set.
				// We don't do UTF-8 detection for multi-byte runes due to
				// false-positives with other encodings (e.g., Shift-JIS).
				// Format says encoding is not UTF-8, so we trust it.
				NonUTF8:  true,

			// #cgo (nocallback|noescape) <function name>
			if fields := strings.Fields(l); len(fields) == 3 {
				directive := fields[1]
				funcName := fields[2]
				if directive == "nocallback" {
					fatalf("#cgo nocallback disabled until Go 1.23")
					f.NoCallbacks[funcName] = true
				} else if directive == "noescape" {
					fatalf("#cgo noescape disabled until Go 1.23")
					f.NoEscapes[funcName] = true
				}
			}

		var prefix string
		switch {
		case format.has(FormatUSTAR | FormatPAX):
			hdr.Format = format
			ustar := tr.blk.toUSTAR()
			prefix = p.parseString(ustar.prefix())

			// For Format detection, check if block is properly formatted since
			// the parser is more liberal than what USTAR actually permits.
			notASCII := func(r rune) bool { return r >= 0x80 }
			if bytes.IndexFunc(tr.blk[:], notASCII) >= 0 {