Tag gensym sourced symbols with metadata

Question

For static analysis tools derived from TANAL it is frequently useful to determine whether a symbol is user defined or the result of code generation. As tools analyzer depends on the Clojure core for evaluation and symbol generation a user wishing to annotate generated symbols must currently provide a binding replacing clojure.core/gensym with a snippet equivalent to the following patch. Such overloading is not appropriate for TANAL, TE* or user code as it is a redefinition of clojure.core behavior which should be standard rather than subjected to users with crowbars.

Answer 1

Comment made by: gtrak

This could eventually help with filtering out def'd symbols like 't131045 coming from reify in CLJS. I've been seeing this behavior with core.async namespaces in an autodoc-cljs proof-of-concept, which could eventually target tools.analyzer.

Answer 2

Comment made by: alexmiller

Re the patch, why not call the Symbol constructor that takes meta instead of with-meta? For performance, it might also be useful to use the same constant map as well.

Answer 3

Comment made by: arrdem

Because the compiler will emit the meta map as a static field the patch as-is will share the same map instance between all annotated symbols. Calling the metadata constructor is reasonable, I'll update the patch.

Answer 4

Comment made by: arrdem

So the metadata constructor of Symbol is private, see https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/Symbol.java#L100. Without changing this directly constructing symbols with metadata is not possible from the core. If you're worried about escaping the var indirection cost of adding metadata via with-meta inlining with-meta is an option, however then we're building two symbols for no good reason. Exposing the currently private metadata constructor is probably the right fix, abet its own ticket.

Answer 5

Comment made by: jafingerhut

From the comments above it appears that this is not planned to be a final version of this patch, but FYI some automated scripts I have found that patch 0001-Annotate-generated-symbols-with-metadata.patch dated Jun 9 2014 applies cleanly to the latest Clojure master as of Jul 1 2014, but Clojure fails to build.

Answer 6

Comment made by: arrdem

Thanks Andy, I'll rework and test it in the morning

Answer 7

Comment made by: arrdem

Because of the work that clojure.lang.Symbol/intern does, exposing and using the metadata constructor directly makes no sense. The updated patch directly invokes clojure.lang.Symbol/withMeta rather than indirecting through clojure.core/with-meta and taking the performance hit of calling through a Var. Builds cleanly on my system.

Answer 8

Comment made by: jafingerhut

Reid, although JIRA can handle multiple attachments with the same name, it can be a bit confusing for people, and for some scripts I have for determining which patches apply and test cleanly. Would you mind renaming one of your patches?

Answer 9

Comment made by: arrdem

3rd and final cut at this patch.

Answer 10

Reference: https://clojure.atlassian.net/browse/CLJ-1442 (reported by arrdem)