Ensure hash(::Platform) is stable (#37734)

This allows us to key dictionaries with `Platform` objects more reliably

base/binaryplatforms.jl

@@ -142,6 +142,20 @@ function Base.setindex!(p::AbstractPlatform, v::String, k::String)
     return p
 end
 
+# Hash definitino to ensure that it's stable
+function Base.hash(p::Platform, h::UInt)
+    h += 0x506c6174666f726d % UInt
+    h = hash(p.tags, h)
+    h = hash(p.compare_strategies, h)
+    return h
+end
+
+# Simple equality definition; for compatibility testing, use `platforms_match()`
+function Base.:(==)(a::Platform, b::Platform)
+    return a.tags == b.tags && a.compare_strategies == b.compare_strategies
+end
+
+
 # Allow us to easily serialize Platform objects
 function Base.repr(p::Platform; context=nothing)
     str = string(
@@ -166,9 +180,6 @@ function Base.show(io::IO, p::Platform)
     print(io, str)
 end
 
-# Simple equality definition; for compatibility testing, use `platforms_match()`
-Base.:(==)(a::AbstractPlatform, b::AbstractPlatform) = tags(a) == tags(b)
-
 function validate_tags(tags::Dict)
     throw_invalid_key(k) = throw(ArgumentError("Key \"$(k)\" cannot have value \"$(tags[k])\""))
     # Validate `arch`

test/binaryplatforms.jl

@@ -136,6 +136,16 @@ end
 
     # Test that trying to set illegal tags fails
     @test_throws ArgumentError p["os"] = "a+b"
+
+    # Test that our `hash()` is stable
+    @test hash(HostPlatform()) == hash(HostPlatform())
+
+    # Test that round-tripping through `triplet` for a does not
+    # maintain equality, as we end up losing the `compare_strategies`:
+    p = Platform("x86_64", "linux"; cuda = v"11")
+    Base.BinaryPlatforms.set_compare_strategy!(p, "cuda", Base.BinaryPlatforms.compare_version_cap)
+    q = parse(Platform, triplet(p))
+    @test q != p
 end
 
 @testset "Triplet parsing" begin
@@ -186,13 +196,12 @@ end
     # Round-trip our little homie through `triplet()`, with some bending
     # of the rules for MacOS and FreeBSD, who have incomplete `os_version`
     # numbers embedded within their triplets.
-    p = HostPlatform()
-    if !Sys.isbsd(p)
-        @test parse(Platform, triplet(p)) == p
-    end
+    p = Platform("x86_64", "linux")
+    @test parse(Platform, triplet(p)) == p
 
     # Also test round-tripping through `repr()`:
-    @test eval(Meta.parse(repr(HostPlatform()))) == HostPlatform()
+    p = Platform("aarch64", "macos"; os_version=v"20", march="armv8_4_crypto_sve")
+    @test eval(Meta.parse(repr(p))) == p
 end
 
 @testset "platforms_match()" begin