Support import renaming through at-compat macro.

Project.toml

@@ -1,6 +1,6 @@
 name = "Compat"
 uuid = "34da2185-b29b-5c13-b0c7-acf172513d20"
-version = "3.20.0"
+version = "3.21.0"
 
 [deps]
 Base64 = "2a0f44e3-6c83-55bd-87e4-b1978d98bd5f"

README.md

@@ -55,6 +55,10 @@ changes in `julia`.
 
 ## Supported features
 
+* Import renaming is available through the `@compat` macro, e.g. `@compat import LinearAlgebra as LA` and
+  `@compat import LinearAlgebra: cholesky as c, lu as l`. *Note:* Import renaming of macros is not
+  supported due to differences in parsing behavior ([#37396]). (since Compat 3.21).
+
 * `Compat.parseatom(text::AbstractString, pos::Integer; filename="none")` parses a single
   atom from `text` starting at index `pos`. Returns a `Tuple` consisting of the
   parsed expression and the index to resume parsing from. ([#35243]) (since Compat 3.20)
@@ -219,3 +223,4 @@ Note that you should specify the correct minimum version for `Compat` in the
 [#37559]: https://github.com/JuliaLang/julia/pull/37559
 [#29634]: https://github.com/JuliaLang/julia/pull/29634
 [#35243]: https://github.com/JuliaLang/julia/pull/35243
+[#37396]: https://github.com/JuliaLang/julia/pull/37396

src/compatmacro.jl

@@ -16,3 +16,53 @@ _compat(ex) = ex
 macro compat(ex)
     esc(_compat(ex))
 end
+
+# Only the import-renaming usage results in multiple arguments.
+# On versions where renaming is supported natively it parses as a
+# single expression and thus takes the single-argument @compat
+# code-path above
+macro compat(ex, exprs...)
+    @assert VERSION < v"1.6.0-DEV.1157"
+    if length(exprs) == 2 && Meta.isexpr(ex, :import, 1) && Meta.isexpr(ex.args[1], :.) &&
+        exprs[1] === :as && exprs[2] isa Symbol
+        # Matches "import Module(.Submodule) as a"
+        lhs = Symbol[ex.args[1].args...]
+        alias = exprs[2]
+        return _create_import_expression([lhs => alias])
+    elseif Meta.isexpr(ex, [:import, :using], 1) &&
+           Meta.isexpr(ex.args[1], :(:)) && length(exprs) % 2 == 0 &&
+           all(x -> x === :as, exprs[1:2:end-1]) &&
+           all(x -> Meta.isexpr(x, :tuple, 2), exprs[2:2:end-2]) &&
+           exprs[end] isa Symbol
+        # Matches "(import|using) Module(.Submodule): a as b(, c as d)
+        syms = Symbol[ ex.args[1].args[2].args[1] ]
+        foreach(x -> x isa Symbol ? push!(syms, x) : append!(syms, x.args), exprs[2:2:end])
+
+        path_aliases = Pair{Vector{Symbol},Symbol}[]
+        init = ex.args[1].args[1].args
+        for i in 1:2:length(syms)
+            push!(path_aliases, Symbol[init; syms[i]] => syms[i+1])
+        end
+        return _create_import_expression(path_aliases)
+    else
+        throw(ArgumentError("invalid use of @compat"))
+    end
+end
+
+function _create_import_expression(path_aliases::Vector{Pair{Vector{Symbol}, Symbol}})
+    # Create an gensymd baremodule to hide names in
+    s = gensym()
+    # Create all import/const exprs
+    import_exprs = Expr[]
+    const_exprs = Expr[]
+    for (path, alias) in path_aliases
+        import_expr = Expr(:import, Expr(:., path...))
+        push!(import_exprs, import_expr)
+        rhs_expr = Expr(:escape, Expr(:., s, QuoteNode(last(path))))
+        const_expr = Expr(:const, Expr(:global, Expr(:(=), alias, rhs_expr)))
+        push!(const_exprs, const_expr)
+    end
+    module_expr = Expr(:module, false, Expr(:escape, s), Expr(:block, import_exprs...))
+    return_expr = Expr(:toplevel, module_expr, const_exprs..., nothing)
+    return return_expr
+end

test/runtests.jl

@@ -753,4 +753,29 @@ end
 
 include("iterators.jl")
 
-nothing
+# Import renaming, https://github.com/JuliaLang/julia/pull/37396,
+# and https://github.com/JuliaLang/julia/pull/37965
+module ImportRename
+    using Compat
+    @compat import LinearAlgebra as LA
+    @compat import LinearAlgebra.BLAS as BL
+    @compat import LinearAlgebra.BLAS: dotc as dc
+    @compat import LinearAlgebra: cholesky as chol, lu as lufact
+    @compat using LinearAlgebra.BLAS: hemm as hm
+end
+
+import .ImportRename
+import LinearAlgebra
+
+@testset "import renaming" begin
+    @test ImportRename.LA === LinearAlgebra
+    @test !isdefined(ImportRename, :LinearAlgebra)
+    @test ImportRename.BL === LinearAlgebra.BLAS
+    @test !isdefined(ImportRename, :BLAS)
+    @test ImportRename.dc === LinearAlgebra.BLAS.dotc
+    @test !isdefined(ImportRename, :dotc)
+    @test ImportRename.chol === LinearAlgebra.cholesky
+    @test ImportRename.lufact === LinearAlgebra.lu
+    @test ImportRename.hm === LinearAlgebra.BLAS.hemm
+    @test !isdefined(ImportRename, :hemm)
+end