It doesn't do this, but clojure-lsp might be able to do this as it keeps all the keywords of the whole project in memory

Thanks!

This has come up before but it isn't possible to detect if the users intentionally matches the literal symbol or not

What we could however detect if when the argument is a certain type (string) and nothing in the case matches that type, we could warn

Ah right. If this was an optional linter, it could be easily be circumvented by using the quoted form for the (rare?) cases you want to match against a symbol

(assuming clj-kondo can detect quoted symbols?)

yes

optional linter can be done for sure

does your case also have a default case? then the type idea would not pan out

user=> (case 'foo-var foo-var "something" nil) ;; warn on this
"something"
user=> (case 'foo-var 'foo-var "something" nil) ;; but not on this
"something"

My personal opinion (without any data to back it) is that using case as-designed (of not dereferencing symbols) is probably not that much used and a confusing bug (for beginners, at least).

huh, the second case is also not valid, quoted symbols in case is never what you want

Why not? It seems to work exactly the same, right?

This is just co-incidental since 'foo-bar expands by the reader into (quote foo-bar) so it would also match the symbol quote:

user=> (case 'quote 'foo-var "something" nil)
"something"

user=> (let [a "foo" b "bar"] (case "foo" 'a :a 'b :b))
Syntax error macroexpanding case at (REPL:1:24).
Duplicate case test constant: quote

True

case is even more confusing than I thought 🙂

all you need to know about case is that the constants are not evaluated

and that you can list multiple constants in a list

I used to know that, but when I did the refactoring I was scratching my head.

I agree that this often confuses people

That is, I was away from the REPL - if I was writing new code I'd have caught it, but since it was old code that was being refactored, then it slipped under my radar.

Can you detect if a symbol in the case expression is actually a valid var?

or a local, I guess

yes, that can be detected

in clj-kondo's codebase there is actually a case statement which matches against the names of vars as symbol so that would be one counter-example, but agreed that this is probably an exception to the rule. also using class names in case is an often source of confusion

I think in most "day-to-day" codebases that linter could be enabled, and then disabled for very specific instances of case statements (still should be an optional linter, I guess)

as an optional linter I wouldn't have a problem with it

I wonder if an optional linter needs to be so accurate as to look into locals or vars, or instead just ban symbols altogether

I'd say just ban symbols. It would be good to scan existing codebases for such usages of case. You can do so using grasp: https://github.com/borkdude/grasp

I always mean to use grasp but I alway forget what it's called. You should pack it in babashka 🙂

So that it could be e.g. invoked by the command line. (Not really suggesting that, I've no idea about it 😄 )

I'll try to cook up a case example ;)

According to grasp here are some counter-examples:

| :line | :column |                                                                                                                                                                                                               :uri |
|-------+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|   176 |      17 |                                                                                jar:file:/Users/borkdude/.m2/repository/cider/cider-nrepl/0.28.6/cider-nrepl-0.28.6.jar!/cider/nrepl/middleware/util/instrument.clj |
|    40 |       5 |                                                                                      jar:file:/Users/borkdude/.m2/repository/cider/cider-nrepl/0.28.6/cider-nrepl-0.28.6.jar!/cider/nrepl/middleware/enlighten.clj |
|   176 |      20 |                                                                   jar:file:/Users/borkdude/.m2/repository/cider/cider-nrepl/0.28.6/cider-nrepl-0.28.6.jar!/cider/nrepl/inlined_deps/fipp/v0v6v26/fipp/clojure.cljc |
|   320 |       5 |                                                  jar:file:/Users/borkdude/.m2/repository/cider/cider-nrepl/0.28.6/cider-nrepl-0.28.6.jar!/cider/nrepl/inlined_deps/toolsreader/v1v3v6/clojure/tools/reader/edn.clj |
|   413 |       5 |                                                      jar:file:/Users/borkdude/.m2/repository/cider/cider-nrepl/0.28.6/cider-nrepl-0.28.6.jar!/cider/nrepl/inlined_deps/toolsreader/v1v3v6/clojure/tools/reader.clj |
|   325 |       5 |                                                    jar:file:/Users/borkdude/.m2/repository/cider/cider-nrepl/0.28.6/cider-nrepl-0.28.6.jar!/cider/nrepl/inlined_deps/toolsreader/v1v3v6/cljs/tools/reader/edn.cljs |
|   434 |       5 |                                                        jar:file:/Users/borkdude/.m2/repository/cider/cider-nrepl/0.28.6/cider-nrepl-0.28.6.jar!/cider/nrepl/inlined_deps/toolsreader/v1v3v6/cljs/tools/reader.cljs |
|   257 |       5 |                                                                                                                       jar:file:/Users/borkdude/.m2/repository/nrepl/nrepl/1.0.0/nrepl-1.0.0.jar!/nrepl/bencode.clj |
|   282 |      16 |                                                                                                                       jar:file:/Users/borkdude/.m2/repository/nrepl/nrepl/1.0.0/nrepl-1.0.0.jar!/nrepl/cmdline.clj |
|  1216 |      23 |                                                                                                               jar:file:/Users/borkdude/.m2/repository/org/babashka/sci/0.3.2/sci-0.3.2.jar!/sci/impl/analyzer.cljc |
|  1284 |      31 |                                                                                                               jar:file:/Users/borkdude/.m2/repository/org/babashka/sci/0.3.2/sci-0.3.2.jar!/sci/impl/analyzer.cljc |
|   144 |       3 |                                                                                                                  jar:file:/Users/borkdude/.m2/repository/org/babashka/sci/0.3.2/sci-0.3.2.jar!/sci/impl/utils.cljc |
|   358 |       4 |                                                                                                            jar:file:/Users/borkdude/.m2/repository/org/clojure/clojure/1.11.0/clojure-1.11.0.jar!/clojure/test.clj |
|   176 |       9 |                                                                                                     jar:file:/Users/borkdude/.m2/repository/org/clojure/clojure/1.11.0/clojure-1.11.0.jar!/clojure/core/server.clj |
|    46 |       6 |                                                                        jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/extract_definition.clj |
|    58 |       5 |                                                                        jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/extract_definition.clj |
|    20 |       7 |      jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsanalyzer/v1v1v0/clojure/tools/analyzer/passes/collect_closed_overs.clj |
|    50 |       5 |                jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsanalyzer/v1v1v0/clojure/tools/analyzer/passes/elide_meta.clj |
|    21 |       6 |          jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsanalyzer/v1v1v0/clojure/tools/analyzer/passes/add_binding_atom.clj |
|   809 |       4 |                                  jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsanalyzer/v1v1v0/clojure/tools/analyzer.clj |
|   320 |       5 |                                  jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsreader/v1v3v6/clojure/tools/reader/edn.clj |
|   413 |       5 |                                      jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsreader/v1v3v6/clojure/tools/reader.clj |
|   325 |       5 |                                    jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsreader/v1v3v6/cljs/tools/reader/edn.cljs |
|   434 |       5 |                                        jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsreader/v1v3v6/cljs/tools/reader.cljs |
|   427 |       4 |                           jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsanalyzerjvm/v1v2v2/clojure/tools/analyzer/jvm.clj |
|   151 |       3 |  jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsanalyzerjvm/v1v2v2/clojure/tools/analyzer/passes/jvm/analyze_host_expr.clj |
|    26 |       3 | jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsanalyzerjvm/v1v2v2/clojure/tools/analyzer/passes/jvm/annotate_host_info.clj |
|   327 |       5 |                                                                                          jar:file:/Users/borkdude/.m2/repository/org/clojure/tools.reader/1.3.4/tools.reader-1.3.4.jar!/cljs/tools/reader/edn.cljs |
|   436 |       5 |                                                                                              jar:file:/Users/borkdude/.m2/repository/org/clojure/tools.reader/1.3.4/tools.reader-1.3.4.jar!/cljs/tools/reader.cljs |
|   415 |       5 |                                                                                            jar:file:/Users/borkdude/.m2/repository/org/clojure/tools.reader/1.3.4/tools.reader-1.3.4.jar!/clojure/tools/reader.clj |
|   322 |       5 |                                                                                        jar:file:/Users/borkdude/.m2/repository/org/clojure/tools.reader/1.3.4/tools.reader-1.3.4.jar!/clojure/tools/reader/edn.clj |

Ah nice, you're running this against .m2?

Here is the first counter-example: https://github.com/clojure-emacs/cider-nrepl/blob/d219ce610d9030108c273fab933538fb3b24d8be/src/cider/nrepl/middleware/util/instrument.clj#L176 You can go through the rest to learn more :) I've just matched against (System/getProperty "java.class.path")

I'll push the grasp code

https://github.com/borkdude/grasp/blob/master/examples/case_symbols.clj

Thanks, I'll run it against our codebase to see

I found one case (!) where it matches the default case as a symbol which it shouldn't, let me fix that

Pushed, less cases now:

| :line | :column |                                                                                                                                                                                     :uri |
|-------+---------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|   176 |      17 |                                                      jar:file:/Users/borkdude/.m2/repository/cider/cider-nrepl/0.28.6/cider-nrepl-0.28.6.jar!/cider/nrepl/middleware/util/instrument.clj |
|    40 |       5 |                                                            jar:file:/Users/borkdude/.m2/repository/cider/cider-nrepl/0.28.6/cider-nrepl-0.28.6.jar!/cider/nrepl/middleware/enlighten.clj |
|   320 |       5 |                        jar:file:/Users/borkdude/.m2/repository/cider/cider-nrepl/0.28.6/cider-nrepl-0.28.6.jar!/cider/nrepl/inlined_deps/toolsreader/v1v3v6/clojure/tools/reader/edn.clj |
|   413 |       5 |                            jar:file:/Users/borkdude/.m2/repository/cider/cider-nrepl/0.28.6/cider-nrepl-0.28.6.jar!/cider/nrepl/inlined_deps/toolsreader/v1v3v6/clojure/tools/reader.clj |
|   325 |       5 |                          jar:file:/Users/borkdude/.m2/repository/cider/cider-nrepl/0.28.6/cider-nrepl-0.28.6.jar!/cider/nrepl/inlined_deps/toolsreader/v1v3v6/cljs/tools/reader/edn.cljs |
|   434 |       5 |                              jar:file:/Users/borkdude/.m2/repository/cider/cider-nrepl/0.28.6/cider-nrepl-0.28.6.jar!/cider/nrepl/inlined_deps/toolsreader/v1v3v6/cljs/tools/reader.cljs |
|  1216 |      23 |                                                                                     jar:file:/Users/borkdude/.m2/repository/org/babashka/sci/0.3.2/sci-0.3.2.jar!/sci/impl/analyzer.cljc |
|  1284 |      31 |                                                                                     jar:file:/Users/borkdude/.m2/repository/org/babashka/sci/0.3.2/sci-0.3.2.jar!/sci/impl/analyzer.cljc |
|    46 |       6 |                                              jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/extract_definition.clj |
|    58 |       5 |                                              jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/extract_definition.clj |
|   809 |       4 |        jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsanalyzer/v1v1v0/clojure/tools/analyzer.clj |
|   320 |       5 |        jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsreader/v1v3v6/clojure/tools/reader/edn.clj |
|   413 |       5 |            jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsreader/v1v3v6/clojure/tools/reader.clj |
|   325 |       5 |          jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsreader/v1v3v6/cljs/tools/reader/edn.cljs |
|   434 |       5 |              jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsreader/v1v3v6/cljs/tools/reader.cljs |
|   427 |       4 | jar:file:/Users/borkdude/.m2/repository/refactor-nrepl/refactor-nrepl/3.5.5/refactor-nrepl-3.5.5.jar!/refactor_nrepl/inlined_deps/toolsanalyzerjvm/v1v2v2/clojure/tools/analyzer/jvm.clj |
|   327 |       5 |                                                                jar:file:/Users/borkdude/.m2/repository/org/clojure/tools.reader/1.3.4/tools.reader-1.3.4.jar!/cljs/tools/reader/edn.cljs |
|   436 |       5 |                                                                    jar:file:/Users/borkdude/.m2/repository/org/clojure/tools.reader/1.3.4/tools.reader-1.3.4.jar!/cljs/tools/reader.cljs |
|   415 |       5 |                                                                  jar:file:/Users/borkdude/.m2/repository/org/clojure/tools.reader/1.3.4/tools.reader-1.3.4.jar!/clojure/tools/reader.clj |
|   322 |       5 |                                                              jar:file:/Users/borkdude/.m2/repository/org/clojure/tools.reader/1.3.4/tools.reader-1.3.4.jar!/clojure/tools/reader/edn.clj |

It would be good to scan your entire .m2 folder and see if any non-tooling libraries have any examples :)

https://github.com/exoscale/lingo/blob/c731061ca6afa880bab67dcbe812f41f0d4b2953/src/exoscale/lingo.cljc#L381

| :line | :column |                                                                :uri |
|-------+---------+---------------------------------------------------------------------|
|    59 |      21 | file:/Users/orestis/dev/nosco/nosco-gamma/cljs/nosco/ui/inputs.cljs |
|   176 |      17 |                                                                     |
|    40 |       5 |                                                                     |
|   320 |       5 |                                                                     |
|   413 |       5 |                                                                     |
|   325 |       5 |                                                                     |
|   434 |       5 |                                                                     |
|    32 |       5 |                                                                     |
|  1087 |      22 |                                                                     |
|    58 |       6 |                                                                     |
|  1216 |      23 |                                                                     |
|  1284 |      31 |                                                                     |
|   427 |       4 |                                                                     |
|   327 |       5 |                                                                     |
|   436 |       5 |                                                                     |
|   415 |       5 |                                                                     |
|   322 |       5 |                                                                     |
|   415 |       5 |                                                                     |
|   322 |       5 |                                                                     |
|   809 |       4 |                                                                     |

https://github.com/sicmutils/sicmutils/blob/02e7a6edaab345e5c6a516f663ecaeb6507cda26/src/sicmutils/expression/render.cljc#L127

oh that's weird, hm

Do you have the newest version of carve?

I put 0.0.3 in the deps as per README and copied the example code

eh carve, I meant grasp, sorry

The newest version is 0.1.4

I went with the latest master for now

I'll update the README

https://github.com/redplanetlabs/proxy-plus/blob/master/src/com/rpl/proxy_plus.clj#L58 an interesting case

https://github.com/mikera/core.matrix/blob/develop/src/main/clojure/clojure/core/matrix/impl/ndarray_magic.clj#L102

Everything else is tools.reader, tools.analyzer, clj-kondo plus variations of those vendored in other deps.

yeah, so it seems mostly clojure-related / low level libraries that tend to use this

or math (sicmutils for examples)

Plus a bug: https://github.com/dm3/clojure.java-time/blob/master/src/java_time/format.clj#L32

you mean, a false positive in carve?

there's no first argument to the case, so the arguments shift around

A bug in the java.time library

oh yes, that's funny

I guess clj-kondo could warn on the first argument to case being a constant

no this is not a bug

there's a threading involved

overuse of threading I'd say ;)

clojure-lsp should have a refactoring to change an if to a cond - but in this case it's even a cond->

clj-kondo would have detected this since it expands -> and ->> and so on, but grasp is mostly for doing research on the feasibility of features for clj-kondo, SCI etc so it doesn't have to be 100% accurate

Ah interesting. So I guess grasp is not meant to be used as e.g. a very custom lint step or for answering definitive questions about a codebase.

it can be but it should be used with this caution in mind

if you want to have it 100% accurate wrt macros (which are always the problem when it comes to static analysis) you could double-check with tools.analyzer or so.

I think grasp could have an option to expand ->, ->> etc as well, but so far I haven't found it worth the effort yet