doc: add script to compute texi files dependencies

Replace the inline awk script with a Perl script which tracks the
dependencies recursively.

This allows to correctly track dependencies for files including files
with a second level include (for example: ffmpeg-devices.texi ->
devices.texi -> outdevs.texi).

This also adds a dependency on perl for computing the dependencies, which
should not be a problem since perl is already required all the way for
building documentation.

This is a variant of commit 628ceac652
which was reverted due to out-of-tree build failure.

configure

@@ -2337,8 +2337,8 @@ ffserver_extralibs='$ldl'
 # documentation
 podpages_deps="perl"
 manpages_deps="perl pod2man"
-htmlpages_deps="texi2html"
-txtpages_deps="makeinfo"
+htmlpages_deps="perl texi2html"
+txtpages_deps="perl makeinfo"
 doc_deps_any="manpages htmlpages podpages txtpages"
 
 # default parameters

doc/Makefile

@@ -61,7 +61,7 @@ documentation: $(DOCS)
 
 examples: $(DOC_EXAMPLES)
 
-TEXIDEP = awk '/^@(verbatim)?include/ { printf "$@: $(@D)/%s\n", $$2 }' <$< >$(@:%=%.d)
+TEXIDEP = perl $(SRC_PATH)/doc/texidep.pl $(SRC_PATH) $< $@ >$(@:%=%.d)
 
 doc/%.txt: TAG = TXT
 doc/%.txt: doc/%.texi

doc/texidep.pl

@@ -0,0 +1,32 @@
+#! /usr/bin/env perl
+
+# This script will print the dependency of a Texinfo file to stdout.
+# texidep.pl <src-path> <input.texi> <output.ext>
+
+use warnings;
+use strict;
+
+die unless @ARGV == 3;
+
+my ($src_path, $root, $target) = @ARGV;
+
+sub print_deps {
+    my ($file, $deps) = @_;
+    $deps->{$file} = 1;
+
+    open(my $fh, "<", "$file") or die "Cannot open file '$file': $!";
+    while (<$fh>) {
+        if (my ($i) = /^\@(?:verbatim)?include\s+(\S+)/) {
+            die "Circular dependency found in file $root\n" if exists $deps->{"doc/$1"};
+            print "$target: doc/$1\n";
+
+            # skip looking for config.texi dependencies, since it has
+            # none, and is not located in the source tree
+            if ("$1" ne "config.texi") {
+                print_deps("$src_path/doc/$1", {%$deps});
+            }
+        }
+    }
+}
+
+print_deps($root, {});