resolv-syms: Generate maps for symtable and dependency lists

This is a first step (low-hanging-fruit kinda thing) for improving the
performance of symbol resolution, where the compiler has to figure out the
dimensions of a symbol by first resolving its dependencies,
recursively.  This is approximately an O(n³) polynomial-time algorithm _per
recursive step_.  Yikes.

This is traditionally where dynamic programming methods would be used, but
that's considerably more difficult in a immutable languages like XSLT, so
I'll do my best without.  (Saxon does offer some support for mutability, but
I'd prefer to avoid it if possible.)

This first change improves performance 30--40%.  For example, on two large
packages we have, build times drop from 55s to 35s and from 1m42s to 1m13s
respectively.

Good start, but much more to be done!

* src/current/include/preproc/package.xsl (preproc:resolv-syms)[lv:package]:
    Compute maps for preproc:symtable and preproc:sym-deps at each recursive
    step.  Pass along via tunneling.
  (preproc:resolv-syms)[preproc:sym]: Use them.

DEV-4354

src/current/include/preproc/package.xsl

@@ -25,6 +25,8 @@
 -->
 <stylesheet version="1.0"
             xmlns="http://www.w3.org/1999/XSL/Transform"
+            xmlns:xs="http://www.w3.org/2001/XMLSchema"
+            xmlns:map="http://www.w3.org/2005/xpath-functions/map"
             xmlns:preproc="http://www.lovullo.com/rater/preproc"
             xmlns:lv="http://www.lovullo.com/rater"
             xmlns:t="http://www.lovullo.com/rater/apply-template"
@@ -565,6 +567,16 @@
   <param name="orig-root" as="element()" />
   <param name="rpcount" select="0" />
 
+  <variable name="symtable-map" as="map( xs:string, element( preproc:sym ) )"
+            select="map:merge(
+                      for $sym in preproc:symtable/preproc:sym
+                        return map{ string( $sym/@name ) : $sym } )" />
+
+  <variable name="symdep-map" as="map( xs:string, element( preproc:sym-dep ) )"
+            select="map:merge(
+                      for $sym-dep in preproc:sym-deps/preproc:sym-dep
+                        return map{ string( $sym-dep/@name ) : $sym-dep } )" />
+
   <!-- arbitrary; intended to prevent infinite recursion -->
   <!-- TODO: same method as for templates; ensure changes, but do not create
        arbitrary limit -->
@@ -588,6 +600,8 @@
 
       <apply-templates mode="preproc:resolv-syms">
         <with-param name="orig-root" select="$orig-root" />
+        <with-param name="symtable-map" select="$symtable-map" tunnel="yes" />
+        <with-param name="symdep-map" select="$symdep-map" tunnel="yes" />
       </apply-templates>
     </copy>
   </variable>
@@ -639,20 +653,25 @@
 
 <template match="preproc:sym[ not( @src ) and @dim='?' ]" mode="preproc:resolv-syms" priority="5">
   <param name="orig-root" as="element()" />
+  <param name="symtable-map" as="map(*)" tunnel="yes" />
+  <param name="symdep-map" as="map(*)" tunnel="yes" />
 
   <variable name="name" select="@name" />
   <variable name="pkg"  as="element( lv:package )"
                 select="root(.)" />
 
-  <variable name="deps" as="element( preproc:sym-dep )*" select="
-      $pkg/preproc:sym-deps/preproc:sym-dep[ @name=$name ]
-    " />
+  <variable name="deps" as="element( preproc:sym-dep )?"
+            select="$symdep-map( $name )" />
 
-  <variable name="depsyms-unresolv" as="element( preproc:sym )*" select="
-      $pkg/preproc:symtable/preproc:sym[
-        @name=$deps/preproc:sym-ref/@name
-      ]
-    " />
+  <!-- TODO: make this fatal -->
+  <if test="empty( $deps ) and not( @no-deps = 'true' )">
+    <message select="concat( 'internal: failed to located dependencies for `',
+                             $name, '''' )" />
+  </if>
+
+  <variable name="depsyms-unresolv" as="element( preproc:sym )*"
+            select="for $ref in $deps/preproc:sym-ref
+                      return $symtable-map( $ref/@name )" />
 
   <variable name="depsyms-resolv">
     <for-each select="$depsyms-unresolv">
@@ -692,12 +711,6 @@
     <when test="
         $depsyms/@dim = '?'
       ">
-      <message>
-        <text>[preproc] deferring `</text>
-          <value-of select="$name" />
-        <text>' dimensions with unresolved dependencies</text>
-      </message>
-
       <!-- schedule repass :x -->
       <sequence select="." />
       <preproc:repass src="preproc:sym resolv-syms"