remove gotmp dir

Author: dzbarsky

go/private/rules/binary.bzl

@@ -485,10 +485,10 @@ def _go_tool_binary_impl(ctx):
         name += ".exe"
 
     out = ctx.actions.declare_file(name)
-
-    # Using pre-declared directory for temporary output to avoid needing to use shell to create it.
-    gotmp = ctx.actions.declare_directory(name + "_gotmp")
     if sdk.goos == "windows":
+        # Using pre-declared directory for temporary output as there is no safe
+        # way under Windows to create unique temporary dir.
+        gotmp = ctx.actions.declare_directory("gotmp")
         cmd = """@echo off
 set GOMAXPROCS=1
 set GOCACHE=%cd%\\{gotmp}\\gocache
@@ -525,16 +525,10 @@ exit /b %GO_EXIT_CODE%
             mnemonic = "GoToolchainBinaryBuild",
         )
     else:
-        # A dummy action to generate `gotmp`; this way the compilation below can avoid listing it in `outputs`.
-        # The net effect is to avoid copying out the GOCACHE when actions run sandboxed.
-        # Incidentally, this makes the reproducibility test pass.
-        ctx.actions.write(
-            output = gotmp,
-            content = "",
-        )
-
-        # In case actions are running unsandboxed, GOCACHE in `gotmp` may have been polluted.
-        # -a flag forces a rebuild so we are not affected by it.
+        # In case actions are running unsandboxed, GOCACHE under `./fake-home` may have been polluted by previous actions.
+        # -a flag forces a rebuild so we don't read anything from it and are unaffected.
+        # For sandboxed actions, `./fake-home` would have been cleared by Bazel after action finished
+        # because it's not a declared output.
         args = ctx.actions.args()
         args.add("build")
         args.add("-a")
@@ -555,14 +549,14 @@ exit /b %GO_EXIT_CODE%
                 # GOCACHE and GOPATH will default themselves to locations under $HOME.
                 # Otherwise we would need to set them explicitly, in which case they must be absolute paths.
                 # That would require a wrapper script/shell dependency.
-                "HOME": gotmp.path,
+                "HOME": "./fake-home",
             },
             inputs = depset(
                 ctx.files.srcs,
                 transitive = [sdk.headers, sdk.srcs, sdk.libs, sdk.tools],
             ),
-            outputs = [out],
             toolchain = None,
+            outputs = [out],
             mnemonic = "GoToolchainBinaryBuild",
         )