From 8c3e6dc4a16406496aa6991f8dc2fb77a96359ea Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Tue, 24 Dec 2019 23:04:58 +0000
Subject: [PATCH] Macro assistance part 2 - syntax for $(eval $(call...))

This can be used to call a macro defined with &:macro.  In combination
these provide a more reasonable macro facility than make's.

Specifically:

* Document the new facility.
* Motivate it in the README.
* Provide the new @nest kind for &${  }, which uses $ddbl as
  a counter to count { and }.
* Implement the {}-counting and nesting end in the main parsing
  loop.  (We must now search for things besides $esc.)
* In extract-doctest, provide a slightly adhoc special case for
  understanding ${eval ...} as an expansion text in the README.
  And do not attempt to test &${ } when already $-doubling.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---
 README                       | 13 +++++++++++++
 generate                     | 19 +++++++++++++++++--
 tests/filter/extract-doctest |  5 +++++
 3 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/README b/README
index 130a1c7..20658ae 100644
--- a/README
+++ b/README
@@ -340,6 +340,19 @@ STUFF $ THINGS	..	STUFF $$ THINGS
 &:endm		..	endef
 	NAME is processed for &
 
+&${..$..} =>	${eval ${call ..$$..}}
+	(matches { } pairs to find the end)
+	content is $-doubled (unless it contains $- to turn that off)
+
+	Together &:macro and &${...} provide a more reasonable macro
+	facility than raw make.  They solve the problem that make
+	expansions cannot directly generate multiple rules, variable,
+	etc.; instead, `$(eval )' must be used, but that re-expands
+	the argument, meaning that all the literal text must be
+	$-doubled.  This applies to the macro text and to the
+	arguments.  Also `$(eval $(call ...))' is an unfortunate syntax.
+	Hence &:macro and &${...}.
+
 While dollar-doubling:
 - - - - - - - - - - -
 
diff --git a/generate b/generate
index 3ccfa0d..52a0ec8 100755
--- a/generate
+++ b/generate
@@ -213,8 +213,19 @@ sub process_input_mk ($$$$) {
 	}
 	for (;;) {
 	    die if $ddbl && defined $buffering_output;
-	    unless (s{^(.*?)$esc}{}) { od $_; last; }
+	    unless (@nest && $nest[0][0] eq 'Eval'
+		    ? s{^(.*?)($esc|[{}])}{}
+		    : s{^(.*?)($esc)}{}) { od $_; last; }
 	    od $1;
+	    if ($2 eq '{') {
+		$ddbl++;
+		next;
+	    } elsif ($2 eq '}') {
+		next if --$ddbl;
+		$pop_nest->('Eval');
+		od '}}';
+		next;
+	    }
 	    if (s{^\\$esc}{}) { od "$$esclitr" }
 	    elsif (s{^\\\$}{}) { oud '$' }
 	    elsif (s{^\\\s+$}{}) { }
@@ -231,7 +242,11 @@ sub process_input_mk ($$$$) {
 	    elsif (s{^\$\+}{}) { $ddbl=1; }
 	    elsif (s{^\$\(}{}) { die unless $ddbl; oud "\$("; }
 	    elsif (s{^\$(\d+)}{}) { die unless $ddbl; oud "\$($1)"; }
-	    elsif (s{^([~^]?)(?=[ \t])}{}) {
+	    elsif (s{^\$\{}{}) {
+		die if $ddbl;
+		od '${eval ${call ';
+		$push_nest->('Eval',1);
+	    } elsif (s{^([~^]?)(?=[ \t])}{}) {
 		my $prefix = $pfxmap{$1} // die;
 		my $after='';
 		if (m{([ \t])$esc}) { ($_,$after) = ($`, $1.$'); }
diff --git a/tests/filter/extract-doctest b/tests/filter/extract-doctest
index 57f5313..d779e00 100755
--- a/tests/filter/extract-doctest
+++ b/tests/filter/extract-doctest
@@ -56,6 +56,9 @@ while (<>) {
 	    $e->{OutTop} = $1 eq 'nothing' ? '' : $1;
 	} elsif (# parse: expect other wordish things to be comments
 		 m{^(?!or\b)\w{2,} }) {
+	} elsif (# adhoc: slightly special case for $(eval $(call
+		 m{^\$\{.*}) {
+	    $e->{Out} .= ' '.$&;
 	} elsif (m/^$/) {
 	} else {
 	    confess "unk rhs $_ ?";
@@ -140,6 +143,8 @@ sub writeout ($) {
 		      my ($e) = @_;
 		      # adhoc: skip &:macro in already-doubling part
 		      return 0 if $e->{In} =~ m{^\&\:macro};
+		      # adhoc: skip &${ ie eval in already-doubling part
+		      return 0 if $e->{In} =~ m{^\&\$\{};
 		      return 0 if $e->{CQ};
 		      return $e->{DD} || !grep {
 			  # If there are two entries with the same In,
-- 
2.30.2