fix #33020, check axes for broadcasted assignment from tuples (#33080)

We avoid computing axes for tuples -- which is a valuable optimization -- but when we explicitly construct a tuple broadcast with axes pre-set (for, e.g., broadcasted assignment), we need to check that those axes are compatible with the ones inside the broadcasted expression before accepting them.

base/broadcast.jl

@@ -260,8 +260,13 @@ of the `Broadcasted` object empty (populated with [`nothing`](@ref)).
     end
     return Broadcasted{Style}(bc.f, bc.args, axes)
 end
-instantiate(bc::Broadcasted{<:Union{AbstractArrayStyle{0}, Style{Tuple}}}) = bc
-
+instantiate(bc::Broadcasted{<:AbstractArrayStyle{0}}) = bc
+# Tuples don't need axes, but when they have axes (for .= assignment), we need to check them (#33020)
+instantiate(bc::Broadcasted{Style{Tuple}, Nothing}) = bc
+function instantiate(bc::Broadcasted{Style{Tuple}})
+    check_broadcast_axes(bc.axes, bc.args...)
+    return bc
+end
 ## Flattening
 
 """

test/broadcast.jl

@@ -663,6 +663,25 @@ end
     @test_throws DimensionMismatch (1, 2) .+ (1, 2, 3)
 end
 
+@testset "broadcasted assignment from tuples and tuple styles (#33020)" begin
+    a = zeros(3)
+    @test_throws DimensionMismatch a .= (1,2)
+    @test_throws DimensionMismatch a .= sqrt.((1,2))
+    a .= (1,)
+    @test all(==(1), a)
+    a .= sqrt.((2,))
+    @test all(==(√2), a)
+    a = zeros(3, 2)
+    @test_throws DimensionMismatch a .= (1,2)
+    @test_throws DimensionMismatch a .= sqrt.((1,2))
+    a .= (1,)
+    @test all(==(1), a)
+    a .= sqrt.((2,))
+    @test all(==(√2), a)
+    a .= (1,2,3)
+    @test a == [1 1; 2 2; 3 3]
+end
+
 @testset "scalar .=" begin
     A = [[1,2,3],4:5,6]
     A[1] .= 0