fix datetime issues

Author: meggart

src/DatasetAPI/Datasets.jl

@@ -249,7 +249,7 @@ function Base.getindex(x::Dataset; var = nothing, kwargs...)
         Dataset(; properties=x.properties, map(ds -> ds => subsetifdimexists(cc[ds]; kwargs...), collect(keys(cc)))...)
     end
 end
-function collectdims(g)
+function collectdims(g; force_datetime=true)
     dlist = Set{Tuple{String,Int,Int}}()
     varnames = get_varnames(g)
     foreach(varnames) do k
@@ -267,7 +267,7 @@ function collectdims(g)
             end
         end
     end
-    outd = Dict(d[1] => (ax = toaxis(d[1], g, d[2], d[3]), offs = d[2]) for d in dlist)
+    outd = Dict(d[1] => (ax=toaxis(d[1], g, d[2], d[3]; force_datetime), offs=d[2]) for d in dlist)
     length(outd) == length(dlist) ||
     throw(ArgumentError("All Arrays must have the same offset"))
     outd
@@ -279,7 +279,7 @@ function round_datetime(dt)
     return DateTime(CFTime.UTInstant{Dates.Millisecond}(ms))
 end
 
-function toaxis(dimname, g, offs, len;prefer_datetime=true)
+function toaxis(dimname, g, offs, len; force_datetime=true)
     axname = Symbol(dimname)
     if !haskey(g, dimname)
         return DD.rebuild(DD.name2dim(axname), 1:len)
@@ -288,14 +288,18 @@ function toaxis(dimname, g, offs, len;prefer_datetime=true)
     aratts = get_var_attrs(g, dimname)
     if match(r"^(days)|(hours)|(seconds)|(months) since",lowercase(get(aratts,"units",""))) !== nothing
         tsteps = try
-            dec = timedecode(ar[:], aratts["units"], lowercase(get(aratts, "calendar", "standard")), prefer_datetime=false)
-            if prefer_datetime
-                round_datetime.(dec)
+            timedecode(ar[:], aratts["units"], lowercase(get(aratts, "calendar", "standard")))
+        catch e
+            if e isa InexactError
+                dec = timedecode(ar[:], aratts["units"], lowercase(get(aratts, "calendar", "standard")), prefer_datetime=false)
+                if force_datetime
+                    round_datetime.(dec)
+                else
+                    dec
+                end
             else
-                dec
+                ar[:]
             end
-        catch
-            ar[:]
         end
         DD.rebuild(DD.name2dim(axname), tsteps[offs+1:end])
     elseif haskey(aratts, "_ARRAYVALUES")
@@ -439,19 +443,20 @@ The default driver will search for available drivers and tries to detect the use
 
 - `skip_keys` are passed as symbols, i.e., `skip_keys = (:a, :b)`
 - `driver=:all`, common options are `:netcdf` or `:zarr`.
+- `force_datetime=false` force conversion when CFTime fails with an InexactError even if milliseconds must be rounded
 
 Example:
 
 ````julia
 ds = open_dataset(f, driver=:zarr, skip_keys = (:c,))
 ````
 """
-function open_dataset(g; skip_keys=(), driver = :all)
+function open_dataset(g; skip_keys=(), driver=:all, force_datetime=false)
     str_skipkeys = string.(skip_keys)
     dsopen = YAXArrayBase.to_dataset(g, driver = driver)
     YAXArrayBase.open_dataset_handle(dsopen) do g 
         isempty(get_varnames(g)) && throw(ArgumentError("Group does not contain datasets."))
-        dimlist = collectdims(g)
+        dimlist = collectdims(g; force_datetime)
         dnames = string.(keys(dimlist))
         varlist = filter(get_varnames(g)) do vn
             upname = uppercase(vn)