JuliaLang · IanButterworth · Dec 14, 2023 · Jan 17, 2022 · Dec 14, 2023 · Dec 14, 2023
diff --git a/NEWS.md b/NEWS.md
@@ -16,6 +16,11 @@ New language features
   particularly useful for holding styling information, and is used extensively
   in the new `StyledStrings` standard library. There is also a new `AnnotatedChar`
   type, that is the equivalent new `AbstractChar` type.
+* `Manifest.toml` files can now be renamed in the format `Manifest-v{major}.{minor}.toml`
+  to be preferentially picked up by the given julia version. i.e. in the same folder,
+  a `Manifest-v1.11.toml` would be used by v1.11 and `Manifest.toml` by every other julia
+  version. This makes managing environments for multiple julia versions at the same time
+  easier ([#43845]).
 
 Language changes
 ----------------

diff --git a/base/loading.jl b/base/loading.jl
@@ -566,7 +566,12 @@ end
 ## generic project & manifest API ##
 
 const project_names = ("JuliaProject.toml", "Project.toml")
-const manifest_names = ("JuliaManifest.toml", "Manifest.toml")
+const manifest_names = (
+    "JuliaManifest-v$(VERSION.major).$(VERSION.minor).toml",
+    "Manifest-v$(VERSION.major).$(VERSION.minor).toml",
+    "JuliaManifest.toml",
+    "Manifest.toml",
+)
 const preferences_names = ("JuliaLocalPreferences.toml", "LocalPreferences.toml")
 
 function locate_project_file(env::String)

diff --git a/doc/src/manual/code-loading.md b/doc/src/manual/code-loading.md
@@ -14,7 +14,7 @@ Code inclusion is quite straightforward and simple: it evaluates the given sourc
 
 A *package* is a source tree with a standard layout providing functionality that can be reused by other Julia projects. A package is loaded by `import X` or  `using X` statements. These statements also make the module named `X`—which results from loading the package code—available within the module where the import statement occurs. The meaning of `X` in `import X` is context-dependent: which `X` package is loaded depends on what code the statement occurs in. Thus, handling of `import X` happens in two stages: first, it determines **what** package is defined to be `X` in this context; second, it determines **where** that particular `X` package is found.
 
-These questions are answered by searching through the project environments listed in [`LOAD_PATH`](@ref) for project files (`Project.toml` or `JuliaProject.toml`), manifest files (`Manifest.toml` or `JuliaManifest.toml`), or folders of source files.
+These questions are answered by searching through the project environments listed in [`LOAD_PATH`](@ref) for project files (`Project.toml` or `JuliaProject.toml`), manifest files (`Manifest.toml` or `JuliaManifest.toml`, or the same names suffixed by `-v{major}.{minor}.toml` for specific versions), or folders of source files.
 
 
 ## Federation of packages
@@ -63,7 +63,7 @@ Each kind of environment defines these three maps differently, as detailed in th
 
 ### Project environments
 
-A project environment is determined by a directory containing a project file called `Project.toml`, and optionally a manifest file called `Manifest.toml`. These files may also be called `JuliaProject.toml` and `JuliaManifest.toml`, in which case `Project.toml` and `Manifest.toml` are ignored. This allows for coexistence with other tools that might consider files called `Project.toml` and `Manifest.toml` significant. For pure Julia projects, however, the names `Project.toml` and `Manifest.toml` are preferred.
+A project environment is determined by a directory containing a project file called `Project.toml`, and optionally a manifest file called `Manifest.toml`. These files may also be called `JuliaProject.toml` and `JuliaManifest.toml`, in which case `Project.toml` and `Manifest.toml` are ignored. This allows for coexistence with other tools that might consider files called `Project.toml` and `Manifest.toml` significant. For pure Julia projects, however, the names `Project.toml` and `Manifest.toml` are preferred. However, from Julia v1.11 onwards, `(Julia)Manifest-v{major}.{minor}.toml` is recognized as a format to make a given julia version use a specific manifest file i.e. in the same folder, a `Manifest-v1.11.toml` would be used by v1.11 and `Manifest.toml` by any other julia version.
 
 The roots, graph and paths maps of a project environment are defined as follows:
 

diff --git a/stdlib/Artifacts/src/Artifacts.jl b/stdlib/Artifacts/src/Artifacts.jl
@@ -18,7 +18,7 @@ function parse_toml(path::String)
     Base.parsed_toml(path)
 end
 
-# keep in sync with Base.project_names and Base.manifest_names
+# keep in sync with Base.project_names
 const artifact_names = ("JuliaArtifacts.toml", "Artifacts.toml")
 
 const ARTIFACTS_DIR_OVERRIDE = Ref{Union{String,Nothing}}(nothing)

diff --git a/stdlib/Artifacts/test/runtests.jl b/stdlib/Artifacts/test/runtests.jl
@@ -258,6 +258,6 @@ end
 @testset "`Artifacts.artifact_names` and friends" begin
     n = length(Artifacts.artifact_names)
     @test length(Base.project_names) == n
-    @test length(Base.manifest_names) == n
+    @test length(Base.manifest_names) == 2n # there are two manifest names per project name
     @test length(Base.preferences_names) == n
 end
diff --git a/test/loading.jl b/test/loading.jl
@@ -795,8 +795,10 @@ end
 @testset "`Base.project_names` and friends" begin
     # Some functions in Pkg assumes that these tuples have the same length
     n = length(Base.project_names)
-    @test length(Base.manifest_names) == n
     @test length(Base.preferences_names) == n
+
+    # there are two manifest names per project name
+    @test length(Base.manifest_names) == 2n
 end
 
 @testset "Manifest formats" begin
@@ -825,6 +827,33 @@ end
     end
 end
 
+@testset "Manifest name preferential loading" begin
+    mktempdir() do tmp
+        proj = joinpath(tmp, "Project.toml")
+        touch(proj)
+        for man_name in (
+            "Manifest.toml",
+            "JuliaManifest.toml",
+            "Manifest-v$(VERSION.major).$(VERSION.minor).toml",
+            "JuliaManifest-v$(VERSION.major).$(VERSION.minor).toml"
+            )
+            touch(joinpath(tmp, man_name))
+            man = basename(Base.project_file_manifest_path(proj))
+            @test man == man_name
+        end
+    end
+    mktempdir() do tmp
+        # check that another version isn't preferred
+        proj = joinpath(tmp, "Project.toml")
+        touch(proj)
+        touch(joinpath(tmp, "Manifest-v1.5.toml"))
+        @test Base.project_file_manifest_path(proj) == nothing
+        touch(joinpath(tmp, "Manifest.toml"))
+        man = basename(Base.project_file_manifest_path(proj))
+        @test man == "Manifest.toml"
+    end
+end
+
 @testset "error message loading pkg bad module name" begin
     mktempdir() do tmp
         old_loadpath = copy(LOAD_PATH)