Merge pull request JuliaLang#40386 from JuliaLang/fe/date-parse

Add type asserts to (try)parse(::TimeType, ...) to help inference.

stdlib/Dates/src/parse.jl

@@ -282,7 +282,7 @@ function Base.parse(::Type{T}, str::AbstractString, df::DateFormat=default_forma
  val = tryparsenext_internal(T, str, pos, len, df, true)
  @assert val !== nothing
  values, endpos = val
- return T(values...)
+ return T(values...)::T
 end
 
 function Base.tryparse(::Type{T}, str::AbstractString, df::DateFormat=default_format(T)) where T<:TimeType
@@ -292,7 +292,7 @@ function Base.tryparse(::Type{T}, str::AbstractString, df::DateFormat=default_fo
  values, endpos = res
  if validargs(T, values...) === nothing
  # TODO: validargs gets called twice, since it's called again in the T constructor
- return T(values...)
+ return T(values...)::T
  end
  return nothing
 end

stdlib/Dates/test/io.jl

@@ -572,4 +572,14 @@ end
  end
 end
 
+@testset "inference with dynamic dateformat string" begin
+ datetime = DateTime(2020, 4, 7)
+ f1() = DateTime("2020-04-07", "yyyy-mm-dd")
+ f2() = DateTime("2020-04-07", DateFormat("yyyy-mm-dd"))
+ f3() = parse(DateTime, "2020-04-07", DateFormat("yyyy-mm-dd"))
+ @test (@inferred f1()) == (@inferred f2()) == (@inferred f3()) == datetime
+ g() = tryparse(DateTime, "2020-04-07", DateFormat("yyyy-mm-dd"))
+ @test (@inferred Nothing g()) == datetime
+end
+
 end