Defer loading the cache for constructing fixed time zones

src/types/fixedtimezone.jl

@@ -72,7 +72,7 @@ UTC+15:45:21
 function FixedTimeZone(s::AbstractString)
     s == "Z" && return UTC_ZERO
 
-    m = match(FIXED_TIME_ZONE_REGEX, s)
+    m = match(FIXED_TIME_ZONE_REGEX, String(s))
     m === nothing && throw(ArgumentError("Unrecognized time zone: $s"))
 
     coefficient = m[:sign] == "-" ? -1 : 1

src/types/timezone.jl

@@ -100,10 +100,15 @@ US/Pacific (UTC-8/UTC-7)
 TimeZone(::AbstractString, ::Class)
 
 function TimeZone(str::AbstractString, mask::Class=Class(:DEFAULT))
-    tz, class = get(_get_tz_cache(), str) do
-        if occursin(FIXED_TIME_ZONE_REGEX, str)
-            FixedTimeZone(str), Class(:FIXED)
-        else
+    # Avoid performing the initial load of the tz cache when only loading a fixed time zone.
+    # Doing this avoids having dependents of TimeZones.jl incurring the initial cache load
+    # cost when using `@tz_str` or `TimeZone` (at the top-level). Specifically, for
+    # packages using `tz"UTC"` we can still support construction at parse time without
+    # adding to the load time of the package when monitoring `@time_imports`.
+    tz, class = if mask & Class(:FIXED) == Class(:FIXED) && occursin(FIXED_TIME_ZONE_REGEX, str)
+        FixedTimeZone(str), Class(:FIXED)
+    else
+        get(_get_tz_cache(), str) do
             throw(ArgumentError("Unknown time zone \"$str\""))
         end
     end
@@ -130,7 +135,7 @@ Africa/Nairobi (UTC+3)
 ```
 """
 macro tz_str(str)
-    TimeZone(str)
+    return TimeZone(str)
 end
 
 """

test/types/fixedtimezone.jl

@@ -25,6 +25,8 @@
     @test FixedTimeZone("+00:30") == FixedTimeZone("UTC+00:30", 1800)
     @test FixedTimeZone("-00:30") == FixedTimeZone("UTC-00:30", -1800)
 
+    @test FixedTimeZone(Test.GenericString("UTC")) == FixedTimeZone("UTC", 0)
+
     @test_throws ArgumentError FixedTimeZone("1")
     @test_throws ArgumentError FixedTimeZone("01")
     @test_throws ArgumentError FixedTimeZone("123")

test/types/timezone.jl

@@ -25,3 +25,20 @@ end
     @test TimeZone("Etc/GMT+12", Class(:LEGACY)) == FixedTimeZone("Etc/GMT+12", -12 * 3600)
     @test TimeZone("Etc/GMT-14", Class(:LEGACY)) == FixedTimeZone("Etc/GMT-14", 14 * 3600)
 end
+
+@testset "fixed time zone cache skip" begin
+    # Reset the tz cache as if we had just loaded the package
+    lock(TimeZones._TZ_CACHE_LOCK) do
+        TimeZones._TZ_CACHE_INITIALIZED[] = false
+        empty!(TimeZones._TZ_CACHE)
+    end
+
+    try
+        @test isempty(TimeZones._TZ_CACHE)
+
+        TimeZone("UTC")  # Construct a `FixedTimeZone` without loading the tz cache
+        @test isempty(TimeZones._TZ_CACHE)
+    finally
+        TimeZones._reload_tz_cache(TimeZones._COMPILED_DIR[])
+    end
+end