Assume effects (#783)

* Compat for `@assume_effects`

Author: Tokazama

Project.toml

@@ -1,6 +1,6 @@
 name = "Compat"
 uuid = "34da2185-b29b-5c13-b0c7-acf172513d20"
-version = "4.3.0"
+version = "4.4.0"
 
 [deps]
 Dates = "ade2ca70-3891-5945-98fb-dc099432e06a"

README.md

@@ -70,6 +70,8 @@ changes in `julia`.
 
 ## Supported features
 
+* `Compat.@assume_effects setting... ex` overrides the compiler's effect modeling for the method definition `ex` on Julia versions that support this feature. Julia version without support just pass back `ex`. ([#43852]) (since Compat 4.4.0)
+
 * `div`, `lcm`, `gcd`, `/`, `rem`, and `mod` will `promote` heterogenous `Dates.Period`s ([`@bdf9ead9`]). (since Compat 4.3.0)
 
 * `stack` combines a collection of slices into one array ([#43334]). (since Compat 4.2.0)

src/Compat.jl

@@ -51,6 +51,15 @@ end
     end
 end
 
+# https://github.com/JuliaLang/julia/pull/43852
+@static if VERSION < v"1.8.0-DEV.1484"
+    macro assume_effects(args...)
+        esc(last(args))
+    end
+else
+    using Base: @assume_effects
+end
+
 if VERSION < v"1.7.0-DEV.119"
     # Part of:
     # https://github.com/JuliaLang/julia/pull/35316

test/runtests.jl

@@ -236,6 +236,15 @@ end
     @test sprint(show, Returns(1.0)) == "Returns{Float64}(1.0)"
 end
 
+# https://github.com/JuliaLang/julia/pull/43852
+@testset "@assume_effects" begin
+    # ensure proper macro hygiene across versions 
+    Compat.@assume_effects :total foo() = true
+    Compat.@assume_effects bar() = true
+    @test foo()
+    @test bar()
+end
+
 # https://github.com/JuliaLang/julia/pull/42125
 @testset "@constprop" begin
     Compat.@constprop :aggressive aggf(x) = Symbol(x)