Name of units in plugins

Spiwack, Arnaud arnaud.spiwack at
Fri Feb 15 08:30:17 UTC 2019

Dear all,

(first, I don't know if this is the best place for questions/discussions
about the GHC API, if not, let me know where to redirect the conversation).

I've been writing a plugin that substitutes call to a function by calls to
another (it's a plugin reimplementation of the assert feature of GHC). And
to be able to point at the names of these two functions, I need to
construct a name (well, and OccName) made of three parts: unit id, module
name, definition name.

This question is about the unit name. Currently I simply use
stringToUnitId. But the real name of my unit has a magic string in it (see
). It's rather unpleasant, it seems to change every time the cabal file
change (at least).

The assert-explainer plugin uses another approach, only using the module
name, then calling findImportedModule (

This is much more robust to changes, but is also less precise (technically,
there can be several imported modules with the same name, with
package-qualified imports).

So, the question is: is there a better, recommended way to recover the
OccName (or Name!) of a function I defined in the same unit my plugin is
defined in.

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