Re: whitespace vs. POSIX

[Eric Blake]

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According to Eric Blake on 10/21/2006 7:56 PM:
> 
> $ printf 'len(\f)
> ' | m4
> 
> should output 1 per a strict reading of POSIX, but outputs 0 on every
> implementation I have access to.  I will wait until the Austin group makes
> a ruling on my aardvark before deciding whether it is worth patching GNU
> m4 to use isblank() instead of isspace() when POSIXLY_CORRECT.

In the meantime, it was worth adding a testcase.  I'm attaching the patch
for the branch, but the patch for head is similar.

2006-10-23  Eric Blake  <address@hidden>

        * doc/m4.texinfo (Macro Arguments): Document that leading space
        in argument collection stops at macro expansion.
        (Incompatibilities): Document POSIX whitespace wording issue.

- --
Life is short - so eat dessert first!

Eric Blake             address@hidden
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Index: doc/m4.texinfo
===================================================================
RCS file: /sources/m4/m4/doc/m4.texinfo,v
retrieving revision 1.1.1.1.2.91
diff -u -p -r1.1.1.1.2.91 m4.texinfo
--- doc/m4.texinfo      21 Oct 2006 02:55:56 -0000      1.1.1.1.2.91
+++ doc/m4.texinfo      24 Oct 2006 03:25:57 -0000
@@ -1113,9 +1113,32 @@ If the name is followed by an opening pa
 collected before the macro is called.  If too few arguments are
 supplied, the missing arguments are taken to be the empty string.
 However, some builtins are documented to behave differently for a
-missing optional argument than for an explicit empty string.  If
-there are too many arguments, the excess arguments are ignored.
-Unquoted leading whitespace is stripped off all arguments.
+missing optional argument than for an explicit empty string.  If there
+are too many arguments, the excess arguments are ignored.  Unquoted
+leading whitespace is stripped off all arguments, but whitespace
+generated by a macro expansion or occuring after a macro that expanded
+to an empty string remains intact.  Whitespace includes space, tab,
+newline, carriage return, vertical tab, and formfeed.
+
address@hidden
+define(`macro', `$1')
address@hidden
+macro( unquoted leading space lost)
address@hidden leading space lost
+macro(` quoted leading space kept')
address@hidden quoted leading space kept
+macro(
+ divert `unquoted space kept after expansion')
address@hidden unquoted space kept after expansion
+macro(macro(`
+')`whitespace from macro expansion kept')
address@hidden
address@hidden from macro expansion kept
+macro(`unquoted trailing whitespace kept'
+)
address@hidden trailing whitespace kept
address@hidden
address@hidden example
 
 Normally @code{m4} will issue warnings if a builtin macro is called
 with an inappropriate number of arguments, but it can be suppressed with
@@ -1136,7 +1159,7 @@ bar(a foo, d)
 @noindent
 is a macro call with four arguments, which are @samp{a }, @samp{b},
 @samp{c} and @samp{d}.  To understand why the first argument contains
-whitespace, remember that leading unquoted whitespace is never part
+whitespace, remember that unquoted leading whitespace is never part
 of an argument, but trailing whitespace always is.
 
 It is possible for a macro's definition to change during argument
@@ -1168,7 +1191,7 @@ define(
 @cindex quoted macro arguments
 @cindex macros, quoted arguments to
 @cindex arguments, quoted macro
-Each argument has leading unquoted whitespace removed.  Within each
+Each argument has unquoted leading whitespace removed.  Within each
 argument, all unquoted parentheses must match.  For example, if
 @var{foo} is a macro,
 
@@ -5388,6 +5411,14 @@ each character of the second and third a
 variables of @env{LANG}, @env{LC_ALL}, @env{LC_CTYPE},
 @env{LC_MESSAGES}, and @env{NLSPATH}, but this has not yet been
 implemented in @acronym{GNU} @code{m4}.
+
address@hidden
address@hidden states that only unquoted leading newlines and blanks
+(that is, space and tab) are ignored when collecting macro arguments.
+However, this appears to be a bug in @acronym{POSIX}, since most
+traditional implementations also ignore all whitespace (formfeed,
+carriage return, and vertical tab).  @acronym{GNU} @code{m4} follows
+tradition and ignores all leading unquoted whitespace.
 @end itemize
 
 @node Other Incompatibilities