Merge pull request #22006 from JuliaLang/nl/hashperiods

Fix Period objects hashing to match ==

Author: omus

base/dates/periods.jl

@@ -443,10 +443,20 @@ Base.promote_rule(::Type{Year}, ::Type{Month}) = Month
 (==)(x::FixedPeriod, y::OtherPeriod) = throw(MethodError(==, (x, y)))
 (==)(x::OtherPeriod, y::FixedPeriod) = throw(MethodError(==, (x, y)))
 
+const fixedperiod_seed = UInt === UInt64 ? 0x5b7fc751bba97516 : 0xeae0fdcb
+const otherperiod_seed = UInt === UInt64 ? 0xe1837356ff2d2ac9 : 0x170d1b00
+# tons() will overflow for periods longer than ~300,000 years, implying a hash collision
+# which is relatively harmless given how infrequent such periods should appear
+Base.hash(x::FixedPeriod, h::UInt) = hash(tons(x), h + fixedperiod_seed)
+# Overflow can also happen here for really long periods (~8e17 years)
+Base.hash(x::Year, h::UInt) = hash(12 * value(x), h + otherperiod_seed)
+Base.hash(x::Month, h::UInt) = hash(value(x), h + otherperiod_seed)
+
 Base.isless(x::FixedPeriod, y::OtherPeriod) = throw(MethodError(isless, (x, y)))
 Base.isless(x::OtherPeriod, y::FixedPeriod) = throw(MethodError(isless, (x, y)))
 
-# truncating conversions to milliseconds and days:
+# truncating conversions to milliseconds, nanoseconds and days:
+# overflow can happen for periods longer than ~300,000 years
 toms(c::Nanosecond)  = div(value(c), 1000000)
 toms(c::Microsecond) = div(value(c), 1000)
 toms(c::Millisecond) = value(c)

test/dates/periods.jl

@@ -394,3 +394,24 @@ cpa = [1y + 1s 1m + 1s 1w + 1s 1d + 1s; 1h + 1s 1mi + 1s 2m + 1s 1s + 1ms]
 
 @test [1y + 1s 1m + 1s; 1w + 1s 1d + 1s] + [1y + 1h 1y + 1mi; 1y + 1s 1y + 1ms] == [2y + 1h + 1s 1y + 1m + 1mi + 1s; 1y + 1w + 2s 1y + 1d + 1s + 1ms]
 @test [1y + 1s 1m + 1s; 1w + 1s 1d + 1s] - [1y + 1h 1y + 1mi; 1y + 1s 1y + 1ms] == [1s-1h 1m + 1s-1y-1mi; 1w-1y 1d + 1s-1y-1ms]
+
+# Equality and hashing between FixedPeriod types
+let types = (Dates.Week, Dates.Day, Dates.Hour, Dates.Minute,
+             Dates.Second, Dates.Millisecond, Dates.Microsecond, Dates.Nanosecond)
+    for i in 1:length(types), j in i:length(types), x in (0, 1, 235, -4677, 15250)
+        T = types[i]
+        U = types[j]
+        y = T(x)
+        z = convert(U, y)
+        @test y == z
+        @test hash(y) == hash(z)
+    end
+end
+
+# Equality and hashing between OtherPeriod types
+for x in (0, 1, 235, -4677, 15250)
+    y = Dates.Year(x)
+    z = convert(Dates.Month, y)
+    @test y == z
+    @test hash(y) == hash(z)
+end