fix(bazel): surface error message when gazelle cant process glob expression (#64214)

Closes DINF-89

Gazelle sometimes have trouble processing glob expressions, and this
isn't reported as a failure even though it ultimately results in the
`BUILD.bazel` not being correctly updated.

## Test plan

* Manual testing

In `client/web/BUILD.bazel`, add a new `src` to the `web_lib` ts_project
target that includes a glob pattern.

```
...
ts_project(
    name = "web_lib",
    srcs = glob(["!src/playwright/*.spec.ts"]) + [
        "src/Index.tsx",
        "src/LegacyLayout.tsx",
        "src/LegacyRouteContext.tsx",
        "src/LegacySourcegraphWebApp.tsx",
        "src/PageError.tsx",
        "src/SearchQueryStateObserver.tsx",
        "src/SourcegraphWebApp.tsx",
...
```

When you run `go run ./dev/sg bazel configure`, the command should fail
with an error message instead of returning exit 0.

## Changelog

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---------

Co-authored-by: Jean-Hadrien Chabran <[email protected]>

Author: BolajiOlajide

dev/ci/bazel-configure.sh

@@ -8,12 +8,27 @@ export PATH
 
 cd "${BUILD_WORKSPACE_DIRECTORY}"
 
-# This fails using rosetta binary, so we just use our normal bazelrc's
-bazel \
-  --bazelrc=.bazelrc \
-  --bazelrc=.aspect/bazelrc/ci.bazelrc \
-  --bazelrc=.aspect/bazelrc/ci.sourcegraph.bazelrc \
-  run //:gazelle
+bazelArgs=("--bazelrc=.bazelrc")
+
+if [ "${CI:-}" ]; then
+  bazelArgs+=("--bazelrc=.aspect/bazelrc/ci.bazelrc")
+  bazelArgs+=("--bazelrc=.aspect/bazelrc/ci.sourcegraph.bazelrc")
+fi
+
+# To enable us access the error message / warning returned by gazelle, we trap stderr in a variable
+# so we can check for glob warnings and report accordingly.
+stderr_output=$(bazel "${bazelArgs[@]}" run //:gazelle 2>&1 >/dev/null)
+
+# If the messages output to stderr includes `could not merge expression`, then it means gazelle
+# encountered an issue while reading a glob expression. We surface that to the user so they can
+# fix.
+if echo "${stderr_output}" | grep -q "could not merge expression"; then
+  echo "${stderr_output}"
+
+  gazelle_err_line=$(echo "${stderr_output}" | grep -m 1 -o '^gazelle:.*')
+  echo "gazelle encountered an issue processing glob expression, the BUILD file is not updated. ${gazelle_err_line}"
+  exit 1
+fi
 
 if [ "${CI:-}" ]; then
   git ls-files --exclude-standard --others | xargs git add --intent-to-add || true

dev/sg/sg_bazel.go

@@ -45,7 +45,7 @@ var bzlgenTargets = map[string]bzlgenTarget{
 	"builds": {
 		order: 1,
 		cmd:   "run",
-		args:  []string{"//:gazelle"},
+		args:  []string{"//:configure"},
 	},
 	"godeps": {
 		cmd:  "run",