diff --git a/NEWS.md b/NEWS.md
index 6db22fa1f8be7..67f99d27536a4 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -78,6 +78,8 @@ Build system changes
New library functions
---------------------
+* `@check cond [msg]` can be used to check if a condition holds and to error otherwise ([#41342])
+
* `in!(x, s::AbstractSet)` will return whether `x` is in `s`, and insert `x` in `s` if not.
* The new `Libc.mkfifo` function wraps the `mkfifo` C function on Unix platforms ([#34587]).
diff --git a/base/error.jl b/base/error.jl
index 37ceb39253e38..627e453b21bb2 100644
--- a/base/error.jl
+++ b/base/error.jl
@@ -237,6 +237,71 @@ macro assert(ex, msgs...)
return :($(esc(ex)) ? $(nothing) : throw(AssertionError($msg)))
end
+# Copied from `macro assert` above for bootstrapping reasons
+function prepare_error(ex, msgs...)
+ msg = isempty(msgs) ? ex : msgs[1]
+ if isa(msg, AbstractString)
+ msg = msg # pass-through
+ elseif !isempty(msgs) && (isa(msg, Expr) || isa(msg, Symbol))
+ # message is an expression needing evaluating
+ msg = :(Main.Base.string($(esc(msg))))
+ elseif isdefined(Main, :Base) && isdefined(Main.Base, :string) && applicable(Main.Base.string, msg)
+ msg = Main.Base.string(msg)
+ else
+ # string() might not be defined during bootstrap
+ msg = quote
+ msg = $(Expr(:quote,msg))
+ isdefined(Main, :Base) ? Main.Base.string(msg) :
+ (Core.println(msg); "Error during bootstrap. See stdout.")
+ end
+ end
+ return msg
+end
+
+"""
+ CheckError([msg])
+
+The checked condition did not evaluate to `true`.
+Optional argument `msg` is a descriptive error string.
+
+# Examples
+```jldoctest
+julia> @check false "this is not true"
+ERROR: CheckError: this is not true
+```
+
+`CheckError` is usually thrown from [`@check`](@ref).
+"""
+struct CheckError <: Exception
+ msg::AbstractString
+end
+CheckError() = CheckError("")
+
+"""
+ @check cond [text]
+
+Throw an [`CheckError`](@ref) if `cond` is `false`.
+Message `text` is optionally displayed upon check failure.
+
+Similar to [`@assert`](@ref), except `@check` is never disabled.
+
+# Examples
+```jldoctest
+julia> @check iseven(3) "3 is an odd number!"
+ERROR: CheckError: 3 is an odd number!
+
+julia> @check isodd(3) "What even are numbers?"
+```
+
+!!! compat "Julia 1.8"
+ This macro was added in Julia 1.8.
+
+"""
+macro check(ex, msgs...)
+ msg = prepare_error(ex, msgs...)
+ return :($(esc(ex)) ? $(nothing) : throw(CheckError($msg)))
+end
+
struct ExponentialBackOff
n::Int
first_delay::Float64
diff --git a/base/errorshow.jl b/base/errorshow.jl
index 74afc191fcc4d..5f9d092191d67 100644
--- a/base/errorshow.jl
+++ b/base/errorshow.jl
@@ -157,6 +157,7 @@ showerror(io::IO, ex::InterruptException) = print(io, "InterruptException:")
showerror(io::IO, ex::ArgumentError) = print(io, "ArgumentError: ", ex.msg)
showerror(io::IO, ex::DimensionMismatch) = print(io, "DimensionMismatch: ", ex.msg)
showerror(io::IO, ex::AssertionError) = print(io, "AssertionError: ", ex.msg)
+showerror(io::IO, ex::CheckError) = print(io, "CheckError: ", ex.msg)
showerror(io::IO, ex::OverflowError) = print(io, "OverflowError: ", ex.msg)
showerror(io::IO, ex::UndefKeywordError) =
diff --git a/base/exports.jl b/base/exports.jl
index 6b783eff9179b..286e8e3400646 100644
--- a/base/exports.jl
+++ b/base/exports.jl
@@ -128,6 +128,7 @@ export
# Exceptions
CanonicalIndexError,
CapturedException,
+ CheckError,
CompositeException,
DimensionMismatch,
EOFError,
@@ -1063,6 +1064,7 @@ export
@polly,
@assert,
+ @check,
@atomic,
@atomicswap,
@atomicreplace,
diff --git a/doc/src/base/base.md b/doc/src/base/base.md
index 64c635ed3043b..1ee4bf0a55575 100644
--- a/doc/src/base/base.md
+++ b/doc/src/base/base.md
@@ -395,10 +395,12 @@ Base.backtrace
Base.catch_backtrace
Base.current_exceptions
Base.@assert
+Base.@check
Base.Experimental.register_error_hint
Base.Experimental.show_error_hints
Base.ArgumentError
Base.AssertionError
+Base.CheckError
Core.BoundsError
Base.CompositeException
Base.DimensionMismatch
diff --git a/test/misc.jl b/test/misc.jl
index e0961c538921a..0dd8e8f17df17 100644
--- a/test/misc.jl
+++ b/test/misc.jl
@@ -5,61 +5,77 @@ include("testhelpers/withlocales.jl")
# Tests that do not really go anywhere else
-# test @assert macro
-@test_throws AssertionError (@assert 1 == 2)
-@test_throws AssertionError (@assert false)
-@test_throws AssertionError (@assert false "this is a test")
-@test_throws AssertionError (@assert false "this is a test" "another test")
-@test_throws AssertionError (@assert false :a)
-let
- try
- @assert 1 == 2
- error("unexpected")
- catch ex
- @test isa(ex, AssertionError)
- @test occursin("1 == 2", ex.msg)
- end
-end
-# test @assert message
-let
- try
- @assert 1 == 2 "this is a test"
- error("unexpected")
- catch ex
- @test isa(ex, AssertionError)
- @test ex.msg == "this is a test"
- end
-end
-# @assert only uses the first message string
-let
- try
- @assert 1 == 2 "this is a test" "this is another test"
- error("unexpected")
- catch ex
- @test isa(ex, AssertionError)
- @test ex.msg == "this is a test"
- end
-end
-# @assert calls string() on second argument
-let
- try
- @assert 1 == 2 :random_object
- error("unexpected")
- catch ex
- @test isa(ex, AssertionError)
- @test !occursin("1 == 2", ex.msg)
- @test occursin("random_object", ex.msg)
+# test @assert and `@check` macro
+# These have the same semantics (except `@assert` is allowed
+# to be disabled in the future), so we test them with the same tests.
+ASSERT_OR_CHECK = Ref(:assert)
+macro assert_or_check(expr...)
+ if ASSERT_OR_CHECK[] == :assert
+ var"@assert"(__source__, __module__, expr...)
+ else
+ var"@check"(__source__, __module__, expr...)
end
end
-# if the second argument is an expression, c
-let deepthought(x, y) = 42
- try
- @assert 1 == 2 string("the answer to the ultimate question: ",
- deepthought(6, 9))
- error("unexpected")
- catch ex
- @test isa(ex, AssertionError)
- @test ex.msg == "the answer to the ultimate question: 42"
+@testset "@$(val)" for val in (:assert, :check)
+ ASSERT_OR_CHECK[] = val
+ @eval begin # eval to delay macro expansion until after we've assigned `val`
+ E = ASSERT_OR_CHECK[] == :assert ? AssertionError : CheckError
+ @test_throws E (@assert_or_check 1 == 2)
+ @test_throws E (@assert_or_check false)
+ @test_throws E (@assert_or_check false "this is a test")
+ @test_throws E (@assert_or_check false "this is a test" "another test")
+ @test_throws E (@assert_or_check false :a)
+ let
+ try
+ @assert_or_check 1 == 2
+ error("unexpected")
+ catch ex
+ @test isa(ex, E)
+ @test occursin("1 == 2", ex.msg)
+ end
+ end
+ # test the macro's message
+ let
+ try
+ @assert_or_check 1 == 2 "this is a test"
+ error("unexpected")
+ catch ex
+ @test isa(ex, E)
+ @test ex.msg == "this is a test"
+ end
+ end
+ # the macro only uses the first message string
+ let
+ try
+ @assert_or_check 1 == 2 "this is a test" "this is another test"
+ error("unexpected")
+ catch ex
+ @test isa(ex, E)
+ @test ex.msg == "this is a test"
+ end
+ end
+ # the macro calls string() on second argument
+ let
+ try
+ @assert_or_check 1 == 2 :random_object
+ error("unexpected")
+ catch ex
+ @test isa(ex, E)
+ @test !occursin("1 == 2", ex.msg)
+ @test occursin("random_object", ex.msg)
+ end
+ end
+ # if the second argument is an expression, c
+ let deepthought(x, y) = 42
+ try
+ @assert_or_check 1 == 2 string("the answer to the ultimate question: ",
+ deepthought(6, 9))
+ error("unexpected")
+ catch ex
+ @test isa(ex, E)
+ @test ex.msg == "the answer to the ultimate question: 42"
+ end
+ end
end
end