normalize paths when writing a project file

src/Types.jl

@@ -10,7 +10,7 @@ import Base.string
 
 using TOML
 import ..Pkg, ..Registry
-import ..Pkg: GitTools, depots, depots1, logdir, set_readonly, safe_realpath, pkg_server, stdlib_dir, stdlib_path, isurl, stderr_f, RESPECT_SYSIMAGE_VERSIONS, atomic_toml_write, create_cachedir_tag
+import ..Pkg: GitTools, depots, depots1, logdir, set_readonly, safe_realpath, pkg_server, stdlib_dir, stdlib_path, isurl, stderr_f, RESPECT_SYSIMAGE_VERSIONS, atomic_toml_write, create_cachedir_tag, normalize_path_for_toml
 import Base.BinaryPlatforms: Platform
 using ..Pkg.Versions
 import FileWatching

src/manifest.jl

@@ -329,14 +329,14 @@ function destructure(manifest::Manifest)::Dict
         entry!(new_entry, "git-tree-sha1", entry.tree_hash)
         entry!(new_entry, "pinned", entry.pinned; default = false)
         path = entry.path
-        if path !== nothing && Sys.iswindows() && !isabspath(path)
-            path = join(splitpath(path), "/")
+        if path !== nothing
+            path = normalize_path_for_toml(path)
         end
         entry!(new_entry, "path", path)
         entry!(new_entry, "entryfile", entry.entryfile)
         repo_source = entry.repo.source
-        if repo_source !== nothing && Sys.iswindows() && !isabspath(repo_source) && !isurl(repo_source)
-            repo_source = join(splitpath(repo_source), "/")
+        if repo_source !== nothing && !isurl(repo_source)
+            repo_source = normalize_path_for_toml(repo_source)
         end
         entry!(new_entry, "repo-url", repo_source)
         entry!(new_entry, "repo-rev", entry.repo.rev)

src/project.jl

@@ -289,7 +289,21 @@ function destructure(project::Project)::Dict
     entry!("entryfile", project.entryfile)
     entry!("deps", merge(project.deps, project._deps_weak))
     entry!("weakdeps", project.weakdeps)
-    entry!("sources", project.sources)
+
+    # Normalize paths in sources to use forward slashes on Windows (matching Manifest.toml behavior)
+    normalized_sources = project.sources
+    if !isempty(project.sources)
+        normalized_sources = Dict{String, Dict{String, String}}()
+        for (name, source) in project.sources
+            normalized_source = copy(source)
+            path = get(source, "path", nothing)
+            if path !== nothing
+                normalized_source["path"] = normalize_path_for_toml(path)
+            end
+            normalized_sources[name] = normalized_source
+        end
+    end
+    entry!("sources", normalized_sources)
     entry!("extras", project.extras)
     entry!("compat", Dict(name => x.str for (name, x) in project.compat))
     entry!("targets", project.targets)

src/utils.jl

@@ -38,6 +38,20 @@ function pathrepr(path::String)
     return "`" * Base.contractuser(path) * "`"
 end
 
+"""
+    normalize_path_for_toml(path::String)
+
+Normalize a path for writing to TOML files (Project.toml/Manifest.toml).
+On Windows, converts relative paths to use forward slashes for cross-platform compatibility.
+Absolute paths are left unchanged as they are platform-specific by nature.
+"""
+function normalize_path_for_toml(path::String)
+    if Sys.iswindows() && !isabspath(path)
+        return join(splitpath(path), "/")
+    end
+    return path
+end
+
 function set_readonly(path)
     for (root, dirs, files) in walkdir(path)
         for file in files

test/misc.jl

@@ -26,6 +26,25 @@ end
     end
 end
 
+@testset "normalize_path_for_toml" begin
+    # Test that relative paths with backslashes are normalized to forward slashes on Windows
+    # and left unchanged on other platforms
+    if Sys.iswindows()
+        @test Pkg.normalize_path_for_toml("foo\\bar\\baz") == "foo/bar/baz"
+        @test Pkg.normalize_path_for_toml("..\\parent\\dir") == "../parent/dir"
+        @test Pkg.normalize_path_for_toml(".\\current") == "./current"
+        # Absolute paths should not be normalized (they're platform-specific)
+        @test Pkg.normalize_path_for_toml("C:\\absolute\\path") == "C:\\absolute\\path"
+        @test Pkg.normalize_path_for_toml("\\\\network\\share") == "\\\\network\\share"
+    else
+        # On Unix-like systems, paths should be unchanged
+        @test Pkg.normalize_path_for_toml("foo/bar/baz") == "foo/bar/baz"
+        @test Pkg.normalize_path_for_toml("../parent/dir") == "../parent/dir"
+        @test Pkg.normalize_path_for_toml("./current") == "./current"
+        @test Pkg.normalize_path_for_toml("/absolute/path") == "/absolute/path"
+    end
+end
+
 @test eltype([PackageSpec(a) for a in []]) == PackageSpec
 
 @testset "PackageSpec version default" begin

test/sources.jl

@@ -51,6 +51,43 @@ temp_pkg_dir() do project_path
             end
         end
     end
+
+    @testset "path normalization in Project.toml [sources]" begin
+        mktempdir() do tmp
+            cd(tmp) do
+                # Create a minimal Project.toml with sources containing a path
+                write(
+                    "Project.toml",
+                    """
+                    name = "TestPackage"
+                    uuid = "12345678-1234-1234-1234-123456789abc"
+
+                    [deps]
+                    LocalPkg = "87654321-4321-4321-4321-cba987654321"
+
+                    [sources]
+                    LocalPkg = { path = "subdir/LocalPkg" }
+                    """
+                )
+
+                # Read the project
+                project = Pkg.Types.read_project("Project.toml")
+
+                # Verify the path is read correctly (will have native separators internally)
+                @test haskey(project.sources, "LocalPkg")
+                @test haskey(project.sources["LocalPkg"], "path")
+
+                # Write it back
+                Pkg.Types.write_project(project, "Project.toml")
+
+                # Read the written file as string and verify forward slashes are used
+                project_content = read("Project.toml", String)
+                @test occursin("path = \"subdir/LocalPkg\"", project_content)
+                # Verify backslashes are NOT in the path (would indicate Windows path wasn't normalized)
+                @test !occursin("path = \"subdir\\\\LocalPkg\"", project_content)
+            end
+        end
+    end
 end
 
 end # module