revert: re-enable sccache in ci (#3369)

After the change in #3366, the docker container now has a working
`sccache` with rust 1.48. This patch reverts the patch that disabled
`sccache` so that we were unblocked.

Fixes #3357

.circleci/config.yml

@@ -10,9 +10,6 @@ jobs:
       GOPATH: /tmp/go
       GO111MODULE: 'on' # must be quoted to force string type instead of boolean type
       SCCACHE_CACHE_SIZE: 1G
-      # XXX: rockstar (23 Nov 2020) - rust 1.48 has issues with sccache. It can be re-enabled
-      # when this bug is addressed: https://github.com/mozilla/sccache/issues/887
-      RUSTC_WRAPPER: ""
     steps:
       - checkout
       # Populate GOPATH/pkg.
@@ -21,13 +18,12 @@ jobs:
           keys:
             - flux-gomod-{{checksum "go.sum"}}
       # Populate Rust cache
-      # Disable use of sccache for now
-      #- restore_cache:
-      #    name: Restoring Rust Cache
-      #    keys:
-      #      - flux-rust-{{ .Branch }}-{{ .Revision }} # Matches when retrying a single run.
-      #      - flux-rust-{{ .Branch }}-                # Matches a new commit on an existing branch.
-      #      - flux-rust-                              # Matches a new branch.
+      - restore_cache:
+          name: Restoring Rust Cache
+          keys:
+            - flux-rust-{{ .Branch }}-{{ .Revision }} # Matches when retrying a single run.
+            - flux-rust-{{ .Branch }}-                # Matches a new commit on an existing branch.
+            - flux-rust-                              # Matches a new branch.
       # Run tests
       - run: make checkfmt
       - run: make checktidy
@@ -45,13 +41,12 @@ jobs:
           key: flux-gomod-{{checksum "go.sum"}}
           paths:
             - /tmp/go/pkg/mod
-      # Disable use of sccache for now
-      #- save_cache:
-      #    name: Saving Rust Cache
-      #    key: flux-rust-{{ .Branch }}-{{ .Revision }}
-      #    paths:
-      #      - "~/.cache/sccache"
-      #    when: always
+      - save_cache:
+          name: Saving Rust Cache
+          key: flux-rust-{{ .Branch }}-{{ .Revision }}
+          paths:
+            - "~/.cache/sccache"
+          when: always
   test-race:
     docker:
       - image: quay.io/influxdb/flux-build:latest
@@ -60,7 +55,6 @@ jobs:
       GOPATH: /tmp/go
       GOFLAGS: -p=8
       GO111MODULE: 'on' # must be quoted to force string type instead of boolean type
-      RUSTC_WRAPPER: ""
     steps:
       - checkout
       # Building go with -race does not use the cache
@@ -79,7 +73,6 @@ jobs:
       GOPATH: /tmp/go
       GOFLAGS: -p=1
       GO111MODULE: 'on' # must be quoted to force string type instead of boolean type
-      RUSTC_WRAPPER: ""
     steps:
       - checkout
       - restore_cache:
@@ -92,8 +85,6 @@ jobs:
   test-valgrind:
     docker:
       - image: quay.io/influxdb/flux-build:latest
-    environment:
-      RUSTC_WRAPPER: ""
     steps:
       - checkout
       - run: make test-valgrind