axis limits = :symmetric (#2600)

* allow axis-lims = :symmetric

* remove show

* add test

src/axes.jl

@@ -533,13 +533,20 @@ function axis_limits(sp, letter, should_widen = default_should_widen(sp[Symbol(l
     has_user_lims = (isa(lims, Tuple) || isa(lims, AVec)) && length(lims) == 2
     if has_user_lims
         lmin, lmax = lims
-        if lmin != :auto && isfinite(lmin)
+        if lmin == :auto
+        elseif isfinite(lmin)
             amin = lmin
         end
-        if lmax != :auto && isfinite(lmax)
+        if lmax == :auto
+        elseif isfinite(lmax)
             amax = lmax
         end
     end
+    if lims == :symmetric
+        aval = max(abs(amin), abs(amax))
+        amin = -aval
+        amax = aval
+    end
     if amax <= amin && isfinite(amin)
         amax = amin + 1.0
     end

test/test_axes.jl

@@ -31,3 +31,8 @@ end
     @test xticks(p) == yticks(p) == zticks(p) == [ticks1, ticks2]
     @test xticks(p[1]) == yticks(p[1]) == zticks(p[1]) == ticks1
 end
+
+@testset "Axis limits" begin
+    pl = plot(1:5, xlims=:symmetric, widen = false)
+    @test Plots.xlims(pl) == (-5, 5)
+end