`json` module incompatible with checked exceptions

[arnetheduck]

json module is broken with regards to checked exceptions (as is most of the std library, this is just one example) - Exception should no longer be raised per recent changes to the Exception hierarchy, yet json and many other modules provide inaccurate exception information in their API.

import json
func f() {.raises: [CatchableError].} = discard parseJson("test")

/usercode/in.nim(3, 58) Error: can raise an unlisted exception: Exception

nim 1.2.6, 1.4.4

[timotheecour]

this PR #16724 attempts to fix this and related issues but is blocked by upgrading csources nim bootstrap version in CI, because bootstrap nim can't support this.

links

• csources2 timotheecour/Nim#251
• CIs: attempt to use csources_v1 #16282 (comment) (NIM_CSOURCES_HASH must be exposed to avoid breaking git bisect + friends)

[arnetheduck]

the root cause in this case is that there are unannotated closure functions down the call stack - generally, the standard library doesn't reason about exception safety - just changing the default eh effect to CatchableError doesn't actually solve the issue - instead the std lib must be reviewed as to where exceptions can be raise, what needs to be released as a consequence and which callbacks and forward declarations actually should be allowed to raise exceptions.

for example, if a function calls a callback that raises, that function needs to be prepared to release resources it allocates (like files) - this rarely happens in the streams modules.

[ringabout]

works on the devel branch