Store a reverse mapping when wiring together graph, detect unused nodes.

The connectivity checking code was previously unable to detect the
following error case:

  local input = nn.Identity()()
  local usedOutput = nn.Linear(20, 10)(input)
  local unusedOutput = nn.Linear(20, 10)(input)
  local gmod = nn.gModule({input}, {usedOutput})

With this fix, when gModule is called it will throw an error, because of
unusedOutput.

This is a backwards incompatible change, but I feel that the current
flexibility is error prone, and I can't see any advantage to it. We have
flushed out a couple of bugs in internal code with this change.

1 files changed, 26 insertions, 0 deletions

diff --git a/test/test_connectivity.lua b/test/test_connectivity.lua
new file mode 100644
index 0000000..99b2539
--- /dev/null
+++ b/test/test_connectivity.lua
@@ -0,0 +1,26 @@
+local totem = require 'totem'
+require 'nngraph'
+local tests = totem.TestSuite()
+local tester = totem.Tester()
+
+function tests.connectivity()
+  -- Store debug info here, need to call debug.getinfo on same line as the
+  -- dangling pointer is declared.
+  local dInfo
+  local input = nn.Identity()()
+  local lin = nn.Linear(20, 10)(input)
+  -- The Sigmoid does not connect to the output, so should cause an error
+  -- when we call gModule.
+  local dangling = nn.Sigmoid()(lin); dInfo = debug.getinfo(1, 'Sl')
+  local actualOutput = nn.Tanh()(lin)
+  local errStr = string.format(
+      'node declared on %%[%s%%]:%d_ does not connect to gmodule output',
+      dInfo.short_src, dInfo.currentline)
+  tester:assertErrorPattern(
+      function()
+        return nn.gModule({input}, {actualOutput})
+      end,
+      errStr)
+end
+
+return tester:add(tests):run()