.forbids pragma: defining forbidden tags (#20050)

* .forbids pragma: defining illegal effects for proc types

This patch intends to define the opposite of the .tags pragma: a way to define effects which are not allowed in a proc.

* updated documentation and changelogs for the forbids pragma

* renamed notTagEffects to forbiddenEffects

* corrected issues of forbids pragma

the forbids pragma didn't handle simple restrictions properly and it also had issues with subtyping

* removed incorrect character from changelog

* added test to cover the interaction of methods and the forbids pragma

* covering the interaction of the tags and forbids pragmas

* updated manual about the forbids pragma

* removed useless statement

* corrected the subtyping of proc types using the forbids pragma

* updated manual for the forbids pragma

* updated documentations for forbids pragma

* updated nim docs

* updated docs with rsttester.nim

* regenerated documentation

* updated rst docs

* Update changelog.md

Co-authored-by: ringabout <43030857+ringabout@users.noreply.github.com>

* updated changelog

* corrected typo

Co-authored-by: ringabout <43030857+ringabout@users.noreply.github.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/tests/effects/teffects14.nim b/tests/effects/teffects14.nim
new file mode 100644
index 000000000..6291d9569
--- /dev/null
+++ b/tests/effects/teffects14.nim
@@ -0,0 +1,15 @@
+discard """
+action: compile
+errormsg: "func1() has an illegal effect: IO"
+line: 15
+"""
+
+type IO = object ## input/output effect
+proc func1(): string {.tags: [IO].} = discard
+proc func2(): string = discard
+
+proc no_IO_please() {.forbids: [IO].} =
+  # this is OK because it didn't define any tag:
+  discard func2()
+  # the compiler prevents this:
+  let y = func1()