Dockerfile, bin(run-tests), tests: set USER (#61)

Better conform with Dockerfile best practices [1]:

    If a service can run without privileges, use `USER` to change to a
    non-root user.

See also the Docker docs on `USER` [2], and the Alpine Linux wiki page
on creating a new user [3].

The commit [4] that added a zig cache significantly speeds up a
`RUN zig test foo` command that's added at the bottom of the Dockerfile.
But it doesn't seem to be a speedup in production.

I suspect that the zig cache isn't found in production, due to
differences in how containers are run (see Exercism's terraform and
tooling-invoker repos [5][6]).

I suspect that this commit may be insufficient to fix the problem, but
it's a step in the right direction. Possible follow-up work includes:

- Setting zig cache environment variables, or passing zig cache
  location options to `zig test`

- Changing the paths of solution files.

- Updating Zig. I saw a recent commit [7] that touches Cache.zig.

Closes: #60
Closes: #62
Refs: #63

[1] https://docs.docker.com/develop/develop-images/dockerfile_best-practices/
[2] https://docs.docker.com/engine/reference/builder/#user
[3] https://wiki.alpinelinux.org/wiki/Setting_up_a_new_user
[4] 82b56af, 2023-08-23, ".dockerignore, Dockerfile: add a zig cache"
[5] https://github.com/exercism/terraform/blob/3ff7b3b5a2f6/terraform/tooling_invoker/ami.sh#L68-L88
[6] https://github.com/exercism/tooling-invoker/blob/88a9d826a746/lib/tooling_invoker/job_processor/exec_docker.rb#L150-L162
[7] ziglang/zig@020105d0dde6
    2023-08-20, "Cache: Fix findPrefix when paths are slightly out of the ordinary"

Author: ee7

Dockerfile

@@ -31,10 +31,13 @@ FROM ${REPO}:${IMAGE} AS runner
 # hadolint ignore=DL3018
 RUN apk add --no-cache jq
 
-COPY --from=builder /opt/zig/ /opt/zig/
-COPY --from=builder /root/.cache/zig/ /root/.cache/zig/
+RUN addgroup ziggroup \
+    && adduser --disabled-password --gecos ziggy --ingroup ziggroup ziggy
+COPY --from=builder --chown=ziggy:ziggroup /opt/zig/ /opt/zig/
+COPY --from=builder --chown=ziggy:ziggroup /root/.cache/zig/ /home/ziggy/.cache/zig/
 ENV PATH=$PATH:/opt/zig
 
+USER ziggy:ziggroup
 WORKDIR /opt/test-runner
-COPY bin/run.sh bin/run.sh
+COPY --chown=ziggy:ziggroup bin/run.sh bin/run.sh
 ENTRYPOINT ["/opt/test-runner/bin/run.sh"]

bin/run-tests.sh

@@ -12,9 +12,15 @@
 # ./bin/run-tests.sh
 
 exit_code=0
+# Copy the tests dir to a temp dir, because in the container the user lacks
+# permissions to write to the tests dir.
+tmp_dir='/tmp/exercism-zig-test-runner'
+rm -rf "${tmp_dir}"
+mkdir -p "${tmp_dir}"
+cp -r tests/* "${tmp_dir}"
 
 # Iterate over all test directories
-for test_dir in tests/*; do
+for test_dir in "${tmp_dir}"/*; do
     test_dir_name=$(basename "${test_dir}")
     test_dir_path=$(realpath "${test_dir}")
     results_file_path="${test_dir_path}/results.json"
@@ -33,8 +39,7 @@ for test_dir in tests/*; do
     if ! diff "${results_file_path}.tmp" "${expected_results_file_path}.tmp"; then
         exit_code=1
     fi
-
-    rm -f "${results_file_path}.tmp" "${expected_results_file_path}.tmp"
 done
 
+rm -rf "${tmp_dir}"
 exit ${exit_code}

tests/example-all-fail/expected_results.json

@@ -1,5 +1,5 @@
 {
   "version": 1,
   "status": "fail",
-  "message": "1/9 test.year not divisible by 4 in common year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/opt/test-runner/tests/example-all-fail/test_example_all_fail.zig:7:5: 0x2247d6 in test.year not divisible by 4 in common year (test)\n    try testing.expect(!leap.leap(2015));\n    ^\n2/9 test.year divisible by 2, not divisible by 4 in common year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/opt/test-runner/tests/example-all-fail/test_example_all_fail.zig:11:5: 0x224896 in test.year divisible by 2, not divisible by 4 in common year (test)\n    try testing.expect(!leap.leap(1970));\n    ^\n3/9 test.year divisible by 4, not divisible by 100 in leap year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/opt/test-runner/tests/example-all-fail/test_example_all_fail.zig:15:5: 0x2248e4 in test.year divisible by 4, not divisible by 100 in leap year (test)\n    try testing.expect(leap.leap(1996));\n    ^\n4/9 test.year divisible by 4 and 5 is still a leap year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/opt/test-runner/tests/example-all-fail/test_example_all_fail.zig:19:5: 0x224934 in test.year divisible by 4 and 5 is still a leap year (test)\n    try testing.expect(leap.leap(1960));\n    ^\n5/9 test.year divisible by 100, not divisible by 400 in common year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/opt/test-runner/tests/example-all-fail/test_example_all_fail.zig:23:5: 0x224986 in test.year divisible by 100, not divisible by 400 in common year (test)\n    try testing.expect(!leap.leap(2100));\n    ^\n6/9 test.year divisible by 100 but not by 3 is still not a leap year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/opt/test-runner/tests/example-all-fail/test_example_all_fail.zig:27:5: 0x2249d6 in test.year divisible by 100 but not by 3 is still not a leap year (test)\n    try testing.expect(!leap.leap(1900));\n    ^\n7/9 test.year divisible by 400 is leap year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/opt/test-runner/tests/example-all-fail/test_example_all_fail.zig:31:5: 0x224a24 in test.year divisible by 400 is leap year (test)\n    try testing.expect(leap.leap(2000));\n    ^\n8/9 test.year divisible by 400 but not by 125 is still a leap year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/opt/test-runner/tests/example-all-fail/test_example_all_fail.zig:35:5: 0x224a74 in test.year divisible by 400 but not by 125 is still a leap year (test)\n    try testing.expect(leap.leap(2400));\n    ^\n9/9 test.year divisible by 200, not divisible by 400 in common year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/opt/test-runner/tests/example-all-fail/test_example_all_fail.zig:39:5: 0x224ac6 in test.year divisible by 200, not divisible by 400 in common year (test)\n    try testing.expect(!leap.leap(1800));\n    ^\n0 passed; 0 skipped; 9 failed."
+  "message": "1/9 test.year not divisible by 4 in common year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/tmp/exercism-zig-test-runner/example-all-fail/test_example_all_fail.zig:7:5: 0x2247d6 in test.year not divisible by 4 in common year (test)\n    try testing.expect(!leap.leap(2015));\n    ^\n2/9 test.year divisible by 2, not divisible by 4 in common year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/tmp/exercism-zig-test-runner/example-all-fail/test_example_all_fail.zig:11:5: 0x224896 in test.year divisible by 2, not divisible by 4 in common year (test)\n    try testing.expect(!leap.leap(1970));\n    ^\n3/9 test.year divisible by 4, not divisible by 100 in leap year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/tmp/exercism-zig-test-runner/example-all-fail/test_example_all_fail.zig:15:5: 0x2248e4 in test.year divisible by 4, not divisible by 100 in leap year (test)\n    try testing.expect(leap.leap(1996));\n    ^\n4/9 test.year divisible by 4 and 5 is still a leap year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/tmp/exercism-zig-test-runner/example-all-fail/test_example_all_fail.zig:19:5: 0x224934 in test.year divisible by 4 and 5 is still a leap year (test)\n    try testing.expect(leap.leap(1960));\n    ^\n5/9 test.year divisible by 100, not divisible by 400 in common year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/tmp/exercism-zig-test-runner/example-all-fail/test_example_all_fail.zig:23:5: 0x224986 in test.year divisible by 100, not divisible by 400 in common year (test)\n    try testing.expect(!leap.leap(2100));\n    ^\n6/9 test.year divisible by 100 but not by 3 is still not a leap year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/tmp/exercism-zig-test-runner/example-all-fail/test_example_all_fail.zig:27:5: 0x2249d6 in test.year divisible by 100 but not by 3 is still not a leap year (test)\n    try testing.expect(!leap.leap(1900));\n    ^\n7/9 test.year divisible by 400 is leap year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/tmp/exercism-zig-test-runner/example-all-fail/test_example_all_fail.zig:31:5: 0x224a24 in test.year divisible by 400 is leap year (test)\n    try testing.expect(leap.leap(2000));\n    ^\n8/9 test.year divisible by 400 but not by 125 is still a leap year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/tmp/exercism-zig-test-runner/example-all-fail/test_example_all_fail.zig:35:5: 0x224a74 in test.year divisible by 400 but not by 125 is still a leap year (test)\n    try testing.expect(leap.leap(2400));\n    ^\n9/9 test.year divisible by 200, not divisible by 400 in common year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/tmp/exercism-zig-test-runner/example-all-fail/test_example_all_fail.zig:39:5: 0x224ac6 in test.year divisible by 200, not divisible by 400 in common year (test)\n    try testing.expect(!leap.leap(1800));\n    ^\n0 passed; 0 skipped; 9 failed."
 }

tests/example-partial-fail/expected_results.json

@@ -1,5 +1,5 @@
 {
   "version": 1,
   "status": "fail",
-  "message": "1/9 test.year not divisible by 4 in common year... OK\n2/9 test.year divisible by 2, not divisible by 4 in common year... OK\n3/9 test.year divisible by 4, not divisible by 100 in leap year... OK\n4/9 test.year divisible by 4 and 5 is still a leap year... OK\n5/9 test.year divisible by 100, not divisible by 400 in common year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/opt/test-runner/tests/example-partial-fail/test_example_partial_fail.zig:23:5: 0x224986 in test.year divisible by 100, not divisible by 400 in common year (test)\n    try testing.expect(!leap.leap(2100));\n    ^\n6/9 test.year divisible by 100 but not by 3 is still not a leap year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/opt/test-runner/tests/example-partial-fail/test_example_partial_fail.zig:27:5: 0x2249d6 in test.year divisible by 100 but not by 3 is still not a leap year (test)\n    try testing.expect(!leap.leap(1900));\n    ^\n7/9 test.year divisible by 400 is leap year... OK\n8/9 test.year divisible by 400 but not by 125 is still a leap year... OK\n9/9 test.year divisible by 200, not divisible by 400 in common year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/opt/test-runner/tests/example-partial-fail/test_example_partial_fail.zig:39:5: 0x224ac6 in test.year divisible by 200, not divisible by 400 in common year (test)\n    try testing.expect(!leap.leap(1800));\n    ^\n6 passed; 0 skipped; 3 failed."
+  "message": "1/9 test.year not divisible by 4 in common year... OK\n2/9 test.year divisible by 2, not divisible by 4 in common year... OK\n3/9 test.year divisible by 4, not divisible by 100 in leap year... OK\n4/9 test.year divisible by 4 and 5 is still a leap year... OK\n5/9 test.year divisible by 100, not divisible by 400 in common year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/tmp/exercism-zig-test-runner/example-partial-fail/test_example_partial_fail.zig:23:5: 0x224986 in test.year divisible by 100, not divisible by 400 in common year (test)\n    try testing.expect(!leap.leap(2100));\n    ^\n6/9 test.year divisible by 100 but not by 3 is still not a leap year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/tmp/exercism-zig-test-runner/example-partial-fail/test_example_partial_fail.zig:27:5: 0x2249d6 in test.year divisible by 100 but not by 3 is still not a leap year (test)\n    try testing.expect(!leap.leap(1900));\n    ^\n7/9 test.year divisible by 400 is leap year... OK\n8/9 test.year divisible by 400 but not by 125 is still a leap year... OK\n9/9 test.year divisible by 200, not divisible by 400 in common year... FAIL (TestUnexpectedResult)\n/opt/zig/lib/std/testing.zig:515:14: 0x2246af in expect (test)\n    if (!ok) return error.TestUnexpectedResult;\n             ^\n/tmp/exercism-zig-test-runner/example-partial-fail/test_example_partial_fail.zig:39:5: 0x224ac6 in test.year divisible by 200, not divisible by 400 in common year (test)\n    try testing.expect(!leap.leap(1800));\n    ^\n6 passed; 0 skipped; 3 failed."
 }