Always write the binary to the mode specific directory

and create a symlink if "out" is specified.

This reduces cache invalidation on mode changes.

Author: mering

go/private/rules/binary.bzl

@@ -136,24 +136,31 @@ def _go_binary_impl(ctx):
     name = ctx.attr.basename
     if not name:
         name = ctx.label.name
-    executable = None
-    if ctx.attr.out:
-        # Use declare_file instead of attr.output(). When users set output files
-        # directly, Bazel warns them not to use the same name as the rule, which is
-        # the common case with go_binary.
-        executable = ctx.actions.declare_file(ctx.attr.out)
-    archive, executable, runfiles = go.binary(
+    archive, executable_binary, runfiles = go.binary(
         go,
         name = name,
         source = go_info,
         gc_linkopts = gc_linkopts(ctx),
         version_file = ctx.version_file,
         info_file = ctx.info_file,
-        executable = executable,
+        executable = None,
     )
     validation_output = archive.data._validation_output
     nogo_diagnostics = archive.data._nogo_diagnostics
 
+    if ctx.attr.out:
+        # Use declare_file instead of attr.output(). When users set output files
+        # directly, Bazel warns them not to use the same name as the rule, which is
+        # the common case with go_binary.
+        executable = ctx.actions.declare_file(ctx.attr.out)
+        ctx.actions.symlink(
+            output = executable,
+            target_file = executable_binary,
+            is_executable = True,
+        )
+    else:
+        executable = executable_binary
+
     providers = [
         archive,
         OutputGroupInfo(
@@ -305,15 +312,11 @@ def _go_binary_kwargs(go_cc_aspects = []):
             "basename": attr.string(
                 doc = """The basename of this binary. The binary
                 basename may also be platform-dependent: on Windows, we add an .exe extension.
+                When not set, it will default to the label name.
                 """,
             ),
             "out": attr.string(
-                doc = """Sets the output filename for the generated executable. When set, `go_binary`
-                will write this file without mode-specific directory prefixes, without
-                linkmode-specific prefixes like "lib", and without platform-specific suffixes
-                like ".exe". Note that without a mode-specific directory prefix, the
-                output file (but not its dependencies) will be invalidated in Bazel's cache
-                when changing configurations.
+                doc = """Sets the output symlink filename for the generated executable.
                 """,
             ),
             "cgo": attr.bool(