Make File.readable? and .writable? follow symlinks on Windows (#1…

…4514)

spec/std/file_spec.cr

@@ -200,9 +200,24 @@ describe "File" do
     it "gives false when a component of the path is a file" do
       File.exists?(datapath("dir", "test_file.txt", "")).should be_false
     end
+
+    it "follows symlinks" do
+      with_tempfile("good_symlink.txt", "bad_symlink.txt") do |good_path, bad_path|
+        File.symlink(File.expand_path(datapath("test_file.txt")), good_path)
+        File.symlink(File.expand_path(datapath("non_existing_file.txt")), bad_path)
+
+        File.exists?(good_path).should be_true
+        File.exists?(bad_path).should be_false
+      end
+    end
   end
 
   describe "executable?" do
+    it "gives true" do
+      crystal = Process.executable_path || pending! "Unable to locate compiler executable"
+      File.executable?(crystal).should be_true
+    end
+
     it "gives false" do
       File.executable?(datapath("test_file.txt")).should be_false
     end
@@ -214,6 +229,17 @@ describe "File" do
     it "gives false when a component of the path is a file" do
       File.executable?(datapath("dir", "test_file.txt", "")).should be_false
     end
+
+    it "follows symlinks" do
+      with_tempfile("good_symlink_x.txt", "bad_symlink_x.txt") do |good_path, bad_path|
+        crystal = Process.executable_path || pending! "Unable to locate compiler executable"
+        File.symlink(File.expand_path(crystal), good_path)
+        File.symlink(File.expand_path(datapath("non_existing_file.txt")), bad_path)
+
+        File.executable?(good_path).should be_true
+        File.executable?(bad_path).should be_false
+      end
+    end
   end
 
   describe "readable?" do
@@ -248,7 +274,28 @@ describe "File" do
           File.readable?(path).should be_false
         end
       end
+
+      it "follows symlinks" do
+        with_tempfile("good_symlink_r.txt", "bad_symlink_r.txt", "unreadable.txt") do |good_path, bad_path, unreadable|
+          File.write(unreadable, "")
+          File.chmod(unreadable, 0o222)
+          pending_if_superuser!
+
+          File.symlink(File.expand_path(datapath("test_file.txt")), good_path)
+          File.symlink(File.expand_path(unreadable), bad_path)
+
+          File.readable?(good_path).should be_true
+          File.readable?(bad_path).should be_false
+        end
+      end
     {% end %}
+
+    it "gives false when the symbolic link destination doesn't exist" do
+      with_tempfile("missing_symlink_r.txt") do |missing_path|
+        File.symlink(File.expand_path(datapath("non_existing_file.txt")), missing_path)
+        File.readable?(missing_path).should be_false
+      end
+    end
   end
 
   describe "writable?" do
@@ -272,6 +319,27 @@ describe "File" do
         File.writable?(path).should be_false
       end
     end
+
+    it "follows symlinks" do
+      with_tempfile("good_symlink_w.txt", "bad_symlink_w.txt", "readonly.txt") do |good_path, bad_path, readonly|
+        File.write(readonly, "")
+        File.chmod(readonly, 0o444)
+        pending_if_superuser!
+
+        File.symlink(File.expand_path(datapath("test_file.txt")), good_path)
+        File.symlink(File.expand_path(readonly), bad_path)
+
+        File.writable?(good_path).should be_true
+        File.writable?(bad_path).should be_false
+      end
+    end
+
+    it "gives false when the symbolic link destination doesn't exist" do
+      with_tempfile("missing_symlink_w.txt") do |missing_path|
+        File.symlink(File.expand_path(datapath("non_existing_file.txt")), missing_path)
+        File.writable?(missing_path).should be_false
+      end
+    end
   end
 
   describe "file?" do

src/crystal/system/win32/file.cr

@@ -164,25 +164,28 @@ module Crystal::System::File
   end
 
   def self.exists?(path, *, follow_symlinks = true)
-    if follow_symlinks
-      path = realpath?(path) || return false
-    end
-    accessible?(path, check_writable: false)
+    accessible?(path, check_writable: false, follow_symlinks: follow_symlinks)
   end
 
   def self.readable?(path) : Bool
-    accessible?(path, check_writable: false)
+    accessible?(path, check_writable: false, follow_symlinks: true)
   end
 
   def self.writable?(path) : Bool
-    accessible?(path, check_writable: true)
+    accessible?(path, check_writable: true, follow_symlinks: true)
   end
 
   def self.executable?(path) : Bool
+    # NOTE: this always follows symlinks:
+    # https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-getbinarytypew#remarks
     LibC.GetBinaryTypeW(System.to_wstr(path), out result) != 0
   end
 
-  private def self.accessible?(path, *, check_writable)
+  private def self.accessible?(path, *, check_writable, follow_symlinks)
+    if follow_symlinks
+      path = realpath?(path) || return false
+    end
+
     attributes = LibC.GetFileAttributesW(System.to_wstr(path))
     return false if attributes == LibC::INVALID_FILE_ATTRIBUTES
     return true if attributes.bits_set?(LibC::FILE_ATTRIBUTE_DIRECTORY)