#!/bin/sh

# Compute the dependencies (direct and transitive) of an object
# This is used to collect all objects needed to link a program.

# Bail out when .d files are missing
test -f "${1%.o}.d" || exit 1

# Check whether $1 contains substring $2
contains(){ test "${1#*$2}" != "$1"; }

# Walk the dependency graph (consinting of the set of all .d files)
# and output the visited nodes (objects).
walk_dag(){
  while read -r line; do
    # skip the first line (file own name)
    contains "$line" ': ' && continue
    # only look up object files
    contains "$line" '.o ' || continue
    line="${line% \\}"
    contains "$visited" "$line" && continue
    visited="$line:$visited"
    printf '%s ' "$line"
    # whether the node is a leaf
    test "$(wc -l < "${line%.o}.d")" -gt 1 && walk_dag < "${line%.o}.d"
  done
}

printf '%s ' "$1"  # the object itself
walk_dag < "${1%.o}.d"