document that asserts might not be running at certain optimization levels (#25610)

Author: KristofferC

NEWS.md

@@ -971,6 +971,8 @@ Deprecated or removed
   * `rand(t::Tuple{Vararg{Int}})` is deprecated in favor of `rand(Float64, t)` or `rand(t...)`;
     `rand(::Tuple)` will have another meaning in the future ([#25429], [#25278]).
 
+  * The `assert` function (and `@assert` macro) have been documented that they are not guaranteed to run under various optimization levels and should therefore not be used to e.g. verify passwords.
+
   * `ObjectIdDict` has been deprecated in favor of `IdDict{Any,Any}` ([#25210]).
 
   * `gc` and `gc_enable` have been deprecated in favor of `GC.gc` and `GC.enable` ([#25616]).

base/error.jl

@@ -113,6 +113,13 @@ systemerror(p, b::Bool; extrainfo=nothing) = b ? throw(Main.Base.SystemError(str
 
 Throw an [`AssertionError`](@ref) if `cond` is `false`.
 Also available as the macro [`@assert`](@ref).
+
+!!! warning
+    An assert might be disabled at various optimization levels.
+    Assert should therefore only be used as a debugging tool
+    and not used for authentication verification (e.g. verifying passwords),
+    nor should side effects needed for the function to work correctly
+    be used inside of asserts.
 """
 assert(x) = x ? nothing : throw(AssertionError())
 
@@ -122,6 +129,13 @@ assert(x) = x ? nothing : throw(AssertionError())
 Throw an [`AssertionError`](@ref) if `cond` is `false`. Preferred syntax for writing assertions.
 Message `text` is optionally displayed upon assertion failure.
 
+!!! warning
+    An assert might be disabled at various optimization levels.
+    Assert should therefore only be used as a debugging tool
+    and not used for authentication verification (e.g. verifying passwords),
+    nor should side effects needed for the function to work correctly
+    be used inside of asserts.
+
 # Examples
 ```jldoctest
 julia> @assert iseven(3) "3 is an odd number!"