Actually check if the loaded backend version mets the compat entries (#4137)

* implement checking backend compat

* format

* handle backends without compat entry

* get version for julia 1.6

Project.toml

@@ -17,6 +17,7 @@ Latexify = "23fbe1c1-3f47-55db-b15f-69d7ec21a316"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 Measures = "442fdcdd-2543-5da2-b0f3-8c86c306513e"
 NaNMath = "77ba4419-2d1f-58cd-9bb1-8ffee604a2e3"
+Pkg = "44cfe95a-1eb2-52ea-b672-e2afdf69b78f"
 PlotThemes = "ccf2f8ad-2431-5c83-bf29-c5338b663b6a"
 PlotUtils = "995b91a9-d308-5afd-9ec6-746e21dbc043"
 Printf = "de0858da-6303-5e67-8744-51eddeeeb8d7"
@@ -45,11 +46,11 @@ JSON = "0.21, 1"
 Latexify = "0.14 - 0.15"
 Measures = "0.3"
 NaNMath = "0.3, 1"
+PGFPlotsX = "1"
 PlotThemes = "2"
 PlotUtils = "1"
 PlotlyBase = "0.7"
 PlotlyJS = "0.18"
-PGFPlotsX = "1"
 PyPlot = "2"
 RecipesBase = "1.2"
 RecipesPipeline = "0.5"

src/Plots.jl

@@ -1,5 +1,7 @@
 module Plots
 
+using Pkg
+
 if isdefined(Base, :Experimental) && isdefined(Base.Experimental, Symbol("@optlevel"))
     @eval Base.Experimental.@optlevel 1
 end
@@ -7,17 +9,26 @@ if isdefined(Base, :Experimental) && isdefined(Base.Experimental, Symbol("@max_m
     @eval Base.Experimental.@max_methods 1
 end
 
-const _current_plots_version = VersionNumber(
-    split(
-        first(
-            filter(
-                line -> occursin("version", line),
-                readlines(normpath(@__DIR__, "..", "Project.toml")),
-            ),
-        ),
-        "\"",
-    )[2],
-)
+const _plots_project = Pkg.Types.read_project(normpath(@__DIR__, "..", "Project.toml"))
+const _current_plots_version = _plots_project.version
+const _plots_compats = _plots_project.compat
+function _check_compat(sim::Module)
+    sim_str = string(sim)
+    if !haskey(_plots_compats, sim_str)
+        return nothing
+    end
+    be_v = Pkg.Types.read_project(joinpath(Base.pkgdir(sim), "Project.toml")).version
+    be_c = _plots_compats[sim_str]
+    if be_c isa String # julia 1.6
+        if be_v in Pkg.Types.semver_spec(be_c)
+            @warn "$sim $be_v is not compatible with this version of Plots. The declared compatibility is $(be_c)."
+        end
+    else
+        if isempty(intersect(be_v, be_c.val))
+            @warn "$sim $be_v is not compatible with this version of Plots. The declared compatibility is $(be_c.str)."
+        end
+    end
+end
 
 using Reexport
 

src/backends.jl

@@ -300,11 +300,23 @@ function _initialize_backend(pkg::AbstractBackend)
     @eval Main begin
         import $sym
         export $sym
+        Plots._check_compat($sym)
     end
 end
 
 _initialize_backend(pkg::GRBackend) = nothing
 
+function _initialize_backend(pkg::PlotlyBackend)
+    try
+        @eval Main begin
+            import PlotlyBase
+        end
+        _check_compat(PlotlyBase)
+    catch
+        @info "For saving to png with the Plotly backend PlotlyBase has to be installed."
+    end
+end
+
 # ------------------------------------------------------------------------------
 # gr
 
@@ -423,16 +435,6 @@ is_marker_supported(::GRBackend, shape::Shape) = true
 # ------------------------------------------------------------------------------
 # plotly
 
-function _initialize_backend(pkg::PlotlyBackend)
-    try
-        @eval Main begin
-            import PlotlyBase
-        end
-    catch
-        @info "For saving to png with the Plotly backend PlotlyBase has to be installed."
-    end
-end
-
 const _plotly_attr = merge_with_base_supported([
     :annotations,
     :legend_background_color,