yyinput() with EOF has inconsistent behavior with documentation

[forewing]

Current Behavior

f863c94 changed the return value of yyinput() from EOF to 0 when encountering an end-of-file:

flex/src/flex.skl

Lines 1970 to 1973 in 3a4af34

	case EOB_ACT_END_OF_FILE:
	{
	if ( yywrap( M4_YY_CALL_ONLY_ARG ) )
	return EOF;

flex/src/flex.skl

Lines 1970 to 1973 in f863c94

	case EOB_ACT_END_OF_FILE:
	{
	if ( yywrap( M4_YY_CALL_ONLY_ARG ) )
	return 0;

Inconsistence

But as documentation showed, yyinput() return EOF when encountering an end-of-file:

flex/doc/flex.texi

Lines 4549 to 4553 in 8b1fbf6

	The @code{input()} routine is not redefinable, though it may be called
	to read characters following whatever has been matched by a rule. If
	@code{input()} encounters an end-of-file the normal @code{yywrap()}
	processing is done. A ``real'' end-of-file is returned by
	@code{input()} as @code{EOF}.

And the example of comments discarding use EOF to check:

flex/doc/flex.texi

Lines 1410 to 1411 in 8b1fbf6

	while ( (c = input()) != '*' &&
	c != EOF )

flex/doc/flex.texi

Lines 1422 to 1426 in 8b1fbf6

	if ( c == EOF )
	{
	error( "EOF in comment" );
	break;
	}

which will never break from the loop in current version.

Possible Solution

The documentation should be updated.

[zmajeed]

Could you provide a reproducible test case that shows yyinput() does not return EOF on end of file?

Isn't the code change you've pointed to what's described in chapter 9 of the doc?

"When the scanner receives an end-of-file indication from YY INPUT, it then checks the yywrap() function. If yywrap() returns false (zero), then it is assumed that the function has gone ahead and set up yyin to point to another input file, and scanning continues. If it returns true (non-zero), then the scanner terminates, returning 0 to its caller."

[zmajeed]

You're right - input() is shown returning EOF on end of file in some parts of flex docs while it returns 0 in other places - I found the Posix spec for input() - https://pubs.opengroup.org/onlinepubs/9699919799/utilities/lex.html - it's supposed to return 0 not EOF on end of file

int input(void)

Returns the next character from the input, or zero on end-of-file. It shall obtain input from the stream pointer yyin, although possibly via an intermediate buffer. Thus, once scanning has begun, the effect of altering the value of yyin is undefined. The character read shall be removed from the input stream of the scanner without any processing by the scanner.