From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Wed, 25 Dec 2019 23:29:40 +0000 (+0000)
Subject: Dollar doubling feature
X-Git-Tag: subdirmk/0.3~64
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?p=subdirmk.git;a=commitdiff_plain;h=f68bcc4648c8cbe549e37159df8bb488178c510c

Dollar doubling feature

This makes it easier to write certain rules commands, and macros
involving eval.  Further enhancements will follow, but for now:

* Document the new facility, including the &-escapes to turn it on and
  off, its effect, and the three within-doubling don't-double escapes.

* Implementation.  Specifically:
   - Rename od to oud (`undoubled').
   - Provide od which does double things if $ddbl (a global) is set.
   - Implement the escapes, and add some error checks.
   - Change `od' to `oud' in `&\$', so that that always produces an
     undoubled $.

* Enhance extract-doctest:
   - Set $e->{DD} to say if it's in `while dollar doubling'.
   - Filter out such entries from the `normal' test - they are not
     legal outside dollar-doubling.
   - Add a dollar-doubling test which includes versions of all
     the normal tests as well as the dollar-doubling ones, and
     which dollar-doubles the outputs when appropriate.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---

diff --git a/README b/README
index 7de4def..d750cb8 100644
--- a/README
+++ b/README
@@ -254,7 +254,7 @@ So pathname syntax is a subset of:
 &&		=>	&&		for convenience in shell runes
 
 &\&		=>	&		general escaping mechanism
-&\$		=>	$
+&\$		=>	$		provided for $-doubling regimes
 &\NEWLINE				eats the newline and vanishes
 
 &$VARIABLE	=>	$(sub_dir_VARIABLE)	or $(TOP_VARIABLE)
@@ -323,6 +323,25 @@ So pathname syntax is a subset of:
 	`all' is extra special: every directory has an `all'
 	target, which corresponds to &TARGETS.
 
+
+Dollar doubling and macro assistance
+------------------------------------
+
+&$+		Starts dollar-doubling
+&$-		Stops dollar-doubling
+	Both are idempotent and local to the file or context.
+
+While dollar-doubling:
+- - - - - - - - - - -
+
+$	=>	$$	including $'s produced by other
+			 &-expansions not mentioned here
+
+&\$	=>	$
+&$NN	=>	$(NN)	where N are digits
+&$(	=>	$(
+
+
 Subdirectory and variable naming
 --------------------------------
 
diff --git a/generate b/generate
index c608e8c..ec47866 100755
--- a/generate
+++ b/generate
@@ -74,7 +74,7 @@ sub oraw {
     print O @_ or die "error writing $writing_output.tmp: $!\n";
 }
 
-sub od { # maybe $-doubled
+sub oud { # undoubled
     if (defined $buffering_output) {
 	$buffering_output .= $_ foreach @_;
 	return;
@@ -82,6 +82,20 @@ sub od { # maybe $-doubled
     oraw @_;
 }
 
+our $ddbl;
+
+sub od { # maybe $-doubled
+    if (!$ddbl) {
+	oud @_;
+	return;
+    }
+    foreach (@_) {
+	my $e = $_;
+	$e =~ s{\$}{\$\$}g;
+	oud $e;
+    }
+}
+
 sub start_output_file ($) {
     close_any_output_file();
     ($writing_output) = @_;
@@ -165,6 +179,8 @@ sub process_input_mk ($$$$) {
 		 );
     $pfxmap{$_} = $srcdirmap{$_}.'/' foreach keys %srcdirmap;
 
+    local $ddbl;
+
     while (<$input>) {
 	if (s#^\s*$esc\:changequote\s+(\S+)\s+$##) {
 	    $$esclitr = $1;
@@ -180,10 +196,11 @@ sub process_input_mk ($$$$) {
 	    $targets->{$t} //= [ ];
 	}
 	for (;;) {
+	    die if $ddbl && defined $buffering_output;
 	    unless (s{^(.*?)$esc}{}) { od $_; last; }
 	    od $1;
 	    if (s{^\\$esc}{}) { od "$$esclitr" }
-	    elsif (s{^\\\$}{}) { od '$' }
+	    elsif (s{^\\\$}{}) { oud '$' }
 	    elsif (s{^\\\s+$}{}) { }
 	    elsif (s{^$esc}{}) { od "$$esclitr$$esclitr" }
 	    elsif (m{^(?=$caps_re)}) { od $var_prefix }
@@ -194,6 +211,10 @@ sub process_input_mk ($$$$) {
 	    elsif (s{^([~^]?)/}{}) { od $pfxmap{$1} }
 	    elsif (s{^\.}{}) { od $dir_name }
 	    elsif (s{^([~^])\.}{}) { od $srcdirmap{$1} }
+	    elsif (s{^\$\-}{}) { $ddbl=undef; }
+	    elsif (s{^\$\+}{}) { $ddbl=1; }
+	    elsif (s{^\$\(}{}) { die unless $ddbl; oud "\$("; }
+	    elsif (s{^\$(\d+)}{}) { die unless $ddbl; oud "\$($1)"; }
 	    elsif (s{^([~^]?)(?=[ \t])}{}) {
 		my $prefix = $pfxmap{$1} // die;
 		my $after='';
diff --git a/tests/filter/extract-doctest b/tests/filter/extract-doctest
index 10dd42a..b63f309 100755
--- a/tests/filter/extract-doctest
+++ b/tests/filter/extract-doctest
@@ -61,6 +61,8 @@ while (<>) {
 	    confess "unk rhs $_ ?";
 	}
 	$e->{CQ} = $in_changequote;
+	# adhoc: rely on this specific section title
+	$e->{DD} = $csection =~ m{^while dollar[- ]doubling}i;
     } else {
 	confess "$_ ?";
     }
@@ -130,7 +132,26 @@ sub writeout ($) {
     oh "# doctest starts $dir_prefix\n";
     write_permode($dir_prefix,
 		  '','','', 'normal',
-		 sub { !$_[0]{CQ} } );
+		 sub { !$_[0]{DD} && !$_[0]{CQ} } );
+    write_permode($dir_prefix,
+		  '&$+', '&$-', "\n",
+		  'dollar doubling',
+		  sub {
+		      my ($e) = @_;
+		      return 0 if $e->{CQ};
+		      return $e->{DD} || !grep {
+			  # If there are two entries with the same In,
+			  # use only the one from the `while dollar
+			  # doubling' section.  So entries there override
+			  # entries in the rest o the file.
+			  $_ ne $e && $_->{In} eq $e->{In}
+		      } @exp;
+		  },
+		  sub {
+		      $_=$_[0];
+		      s/\$/\$\$/g unless $_[1]{DD};
+		      $_;
+		  } );
     write_permode($dir_prefix,
 		  "&:changequote NEWQUOTE\n",
 		  "NEWQUOTE:changequote &\n",