Analyze and document levelization:

* Markdown explanation of what levelization is, the intended levels, as
  well as the process used to determine dependencies
* Shell script finds all dependencies, groups them, and finds cyclic
  dependencies and maps out non-cyclic dependencies.
* Github job to run the script and fail if anything changes. Should
  catch introduction of new dependencies and new problems. Will also
  detect changes if problems or dependencies are removed.

Builds/levelization/levelization.sh

@@ -0,0 +1,127 @@
+#!/bin/bash
+
+# Usage: levelization.sh
+# This script takes no parameters, reads no environment variables,
+# and can be run from any directory, as long as it is in the expected
+# location in the repo.
+
+pushd $( dirname $0 )
+
+if [ -v PS1 ]
+then
+  # if the shell is interactive, clean up any flotsam before analyzing
+  git clean -ix
+fi
+
+rm -rfv results
+mkdir results
+includes="$( pwd )/results/rawincludes.txt"
+pushd ../..
+echo Raw includes:
+grep -r '#include.*/.*\.h' src/ripple/ src/test/ | \
+    grep -v boost | tee ${includes}
+popd
+pushd results
+
+oldifs=${IFS}
+IFS=:
+mkdir includes
+mkdir includedby
+echo Build levelization paths
+exec 3< ${includes} # open rawincludes.txt for input
+while read -r -u 3 file include
+do
+    level=$( echo ${file} | cut -d/ -f 2,3 )
+    # If the "level" indicates a file, cut off the filename
+    if [[ "${level##*.}" != "${level}" ]]
+    then
+        # Use the "toplevel" label as a workaround for `sort`
+        # inconsistencies between different utility versions
+        level="$( dirname ${level} )/toplevel"
+    fi
+    level=$( echo ${level} | tr '/' '.' )
+
+    includelevel=$( echo ${include} | sed 's/.*["<]//; s/[">].*//' | \
+        cut -d/ -f 1,2 )
+    if [[ "${includelevel##*.}" != "${includelevel}" ]]
+    then
+        # Use the "toplevel" label as a workaround for `sort`
+        # inconsistencies between different utility versions
+        includelevel="$( dirname ${includelevel} )/toplevel"
+    fi
+    includelevel=$( echo ${includelevel} | tr '/' '.' )
+
+    if [[ "$level" != "$includelevel" ]]
+    then
+        echo $level $includelevel | tee -a paths.txt
+    fi
+done
+echo Sort and dedup paths
+sort -ds paths.txt | uniq -c | tee sortedpaths.txt
+mv sortedpaths.txt paths.txt
+exec 3>&- #close fd 3
+IFS=${oldifs}
+unset oldifs
+
+echo Split into flat-file database
+exec 4<paths.txt # open paths.txt for input
+while read -r -u 4 count level include
+do
+    echo ${include} ${count} | tee -a includes/${level}
+    echo ${level} ${count} | tee -a includedby/${include}
+done
+exec 4>&- #close fd 4
+
+loops="$( pwd )/loops.txt"
+ordering="$( pwd )/ordering.txt"
+pushd includes
+echo Search for loops
+# Redirect stdout to a file
+exec 4>&1
+exec 1>"${loops}"
+for source in *
+do
+  if [[ -f "$source" ]]
+  then
+    exec 5<"${source}" # open for input
+    while read -r -u 5 include includefreq
+    do
+      if [[ -f $include ]]
+      then
+        if grep -q -w $source $include
+        then
+          if grep -q -w "Loop: $include $source" "${loops}"
+          then
+            continue
+          fi
+          sourcefreq=$( grep -w $source $include | cut -d\  -f2 )
+          echo "Loop: $source $include"
+          # If the counts are close, indicate that the two modules are
+          # on the same level, though they shouldn't be
+          if [[ $(( $includefreq - $sourcefreq )) -gt 3 ]]
+          then
+              echo -e "  $source > $include\n"
+          elif [[ $(( $sourcefreq - $includefreq )) -gt 3 ]]
+          then
+              echo -e "  $include > $source\n"
+          elif [[ $sourcefreq -eq $includefreq ]]
+          then
+              echo -e "  $include == $source\n"
+          else
+              echo -e "  $include ~= $source\n"
+          fi
+        else
+          echo "$source > $include" >> "${ordering}"
+        fi
+      fi
+    done
+    exec 5>&- #close fd 5
+  fi
+done
+exec 1>&4 #close fd 1
+exec 4>&- #close fd 4
+cat "${ordering}"
+cat "${loops}"
+popd
+popd
+popd