fix(linker): don't symlink on Windows (#1253)

1) FAT (FAT32, exFAT, etc.) file systems doesn't support symlinks.
2) You need administrator access in order to create symlinks.

This was working for me locally because I'm running a NTFS fs with
"Developer Mode" enabled in Windows 10, which bypasses administrator
requirement for mklink.

Instead we uv_fs_rename() links. This should effectively be the same,
but will require special handling down the road if/when for example
multiple package versions can be installed at the same time. When
unlinking a package the renamed files should me moved back into the
package installation directory, instead of simply being unlinked (i.e.
removed).

Closes #1251.

2 files changed, 79 insertions, 17 deletions

diff --git a/lua/mason-core/installer/linker.lua b/lua/mason-core/installer/linker.lua
index 98d1d30f..c9a87027 100644
--- a/lua/mason-core/installer/linker.lua
+++ b/lua/mason-core/installer/linker.lua
@@ -50,7 +50,7 @@ end
 ---@async
 ---@param context InstallContext
 ---@param link_context LinkContext
----@param link_fn async fun(dest: string, target: string): Result
+---@param link_fn async fun(new_abs_path: string, target_abs_path: string): Result
 local function link(context, link_context, link_fn)
     log.trace("Linking", context.package, link_context.type, context.links[link_context.type])
     return Result.try(function(try)
@@ -58,13 +58,13 @@ local function link(context, link_context, link_fn)
             if platform.is.win and link_context == LinkContext.BIN then
                 name = ("%s.cmd"):format(name)
             end
-            local dest_abs_path = link_context.prefix(name)
+            local new_abs_path = link_context.prefix(name)
             local target_abs_path = path.concat { context.package:get_install_path(), rel_path }
 
             do
                 -- 1. Ensure destination directory exists
                 a.scheduler()
-                local dir = vim.fn.fnamemodify(dest_abs_path, ":h")
+                local dir = vim.fn.fnamemodify(new_abs_path, ":h")
                 if not fs.async.dir_exists(dir) then
                     try(Result.pcall(fs.async.mkdirp, dir))
                 end
@@ -74,11 +74,11 @@ local function link(context, link_context, link_fn)
                 -- 2. Ensure source file exists and target doesn't yet exist OR if --force unlink target if it already
                 -- exists.
                 if context.opts.force then
-                    if fs.async.file_exists(dest_abs_path) then
-                        try(Result.pcall(fs.async.unlink, dest_abs_path))
+                    if fs.async.file_exists(new_abs_path) then
+                        try(Result.pcall(fs.async.unlink, new_abs_path))
                     end
-                elseif fs.async.file_exists(dest_abs_path) then
-                    return Result.failure(("%q is already linked."):format(dest_abs_path, name))
+                elseif fs.async.file_exists(new_abs_path) then
+                    return Result.failure(("%q is already linked."):format(new_abs_path, name))
                 end
                 if not fs.async.file_exists(target_abs_path) then
                     return Result.failure(("Link target %q does not exist."):format(target_abs_path))
@@ -86,7 +86,7 @@ local function link(context, link_context, link_fn)
             end
 
             -- 3. Execute link.
-            try(link_fn(dest_abs_path, target_abs_path))
+            try(link_fn(new_abs_path, target_abs_path))
             context.receipt:with_link(link_context.type, name, rel_path)
         end
     end)
@@ -95,17 +95,25 @@ end
 ---@param context InstallContext
 ---@param link_context LinkContext
 local function symlink(context, link_context)
-    return link(context, link_context, function(target, dest)
-        return Result.pcall(fs.async.symlink, dest, target)
+    return link(context, link_context, function(new_abs_path, target_abs_path)
+        return Result.pcall(fs.async.symlink, target_abs_path, new_abs_path)
+    end)
+end
+
+---@param context InstallContext
+---@param link_context LinkContext
+local function rename(context, link_context)
+    return link(context, link_context, function(new_abs_path, target_abs_path)
+        return Result.pcall(fs.async.rename, target_abs_path, new_abs_path)
     end)
 end
 
 ---@param context InstallContext
 local function win_bin_wrapper(context)
-    return link(context, LinkContext.BIN, function(dest, target)
+    return link(context, LinkContext.BIN, function(new_abs_path, target_abs_path)
         return Result.pcall(
             fs.async.write_file,
-            dest,
+            new_abs_path,
             _.dedent(([[
                 @ECHO off
                 GOTO start
@@ -117,7 +125,7 @@ local function win_bin_wrapper(context)
                 CALL :find_dp0
 
                 endLocal & goto #_undefined_# 2>NUL || title %%COMSPEC%% & "%s" %%*
-            ]]):format(target))
+            ]]):format(target_abs_path))
         )
     end)
 end
@@ -130,11 +138,13 @@ function M.link(context)
     return Result.try(function(try)
         if platform.is.win then
             try(win_bin_wrapper(context))
+            try(rename(context, LinkContext.SHARE))
+            try(rename(context, LinkContext.OPT))
         else
             try(symlink(context, LinkContext.BIN))
+            try(symlink(context, LinkContext.SHARE))
+            try(symlink(context, LinkContext.OPT))
         end
-        try(symlink(context, LinkContext.SHARE))
-        try(symlink(context, LinkContext.OPT))
     end)
 end
 
diff --git a/tests/mason-core/installer/linker_spec.lua b/tests/mason-core/installer/linker_spec.lua
index ac66b212..0a2b62ab 100644
--- a/tests/mason-core/installer/linker_spec.lua
+++ b/tests/mason-core/installer/linker_spec.lua
@@ -21,7 +21,7 @@ describe("linker", function()
     local platform
 
     before_each(function()
-        package.loaded["mason-core.installer.platform"] = nil
+        package.loaded["mason-core.platform"] = nil
         package.loaded["mason-core.installer.linker"] = nil
         platform = require "mason-core.platform"
         linker = require "mason-core.installer.linker"
@@ -131,7 +131,10 @@ describe("linker", function()
             local ctx = InstallContextGenerator(handle)
             ctx.links.share["nested/path/share-file"] = path.concat { "nested", "path", "to", "share-file" }
             ctx.links.share["share-file"] = "share-file"
-            assert.is_true(linker.link(ctx):is_success())
+
+            local result = linker.link(ctx)
+
+            assert.is_true(result:is_success())
 
             assert.spy(fs.async.write_file).was_called(0)
             assert.spy(fs.async.symlink).was_called(2)
@@ -148,4 +151,53 @@ describe("linker", function()
             assert.spy(fs.async.mkdirp).was_called_with(path.share_prefix "nested/path")
         end)
     )
+
+    it("should rename share files on Windows", function()
+        platform.is.darwin = false
+        platform.is.mac = false
+        platform.is.linux = false
+        platform.is.unix = false
+        platform.is.win = true
+
+        local dummy = registry.get_package "dummy"
+        stub(fs.async, "mkdirp")
+        stub(fs.async, "dir_exists")
+        stub(fs.async, "file_exists")
+        stub(fs.async, "rename")
+
+        -- mock non-existent dest files
+        fs.async.file_exists.on_call_with(path.share_prefix "share-file").returns(false)
+        fs.async.file_exists.on_call_with(path.share_prefix(path.concat { "nested", "share-file" })).returns(false)
+
+        fs.async.dir_exists.on_call_with(path.share_prefix()).returns(false)
+        fs.async.dir_exists.on_call_with(path.share_prefix "nested/path").returns(false)
+
+        -- mock existent source files
+        fs.async.file_exists.on_call_with(path.concat { dummy:get_install_path(), "share-file" }).returns(true)
+        fs.async.file_exists
+            .on_call_with(path.concat { dummy:get_install_path(), "nested", "path", "to", "share-file" })
+            .returns(true)
+
+        local handle = InstallHandleGenerator "dummy"
+        local ctx = InstallContextGenerator(handle)
+        ctx.links.share["nested/path/share-file"] = path.concat { "nested", "path", "to", "share-file" }
+        ctx.links.share["share-file"] = "share-file"
+
+        local result = linker.link(ctx)
+
+        assert.is_true(result:is_success())
+
+        assert.spy(fs.async.rename).was_called(2)
+        assert
+            .spy(fs.async.rename)
+            .was_called_with(path.concat { dummy:get_install_path(), "share-file" }, path.share_prefix "share-file")
+        assert.spy(fs.async.rename).was_called_with(
+            path.concat { dummy:get_install_path(), "nested", "path", "to", "share-file" },
+            path.share_prefix "nested/path/share-file"
+        )
+
+        assert.spy(fs.async.mkdirp).was_called(2)
+        assert.spy(fs.async.mkdirp).was_called_with(path.share_prefix())
+        assert.spy(fs.async.mkdirp).was_called_with(path.share_prefix "nested/path")
+    end)
 end)