fuzz: Fix upstream build

The upstream build is failing with:
/usr/local/bin/compile_native_go_fuzzer: line 35: addimport: command
not found

The changes uses the upstream approach to install the missing commands.
Note that one of the reasons of the unilateral failure upstream is due
to the base image changed in:
google/oss-fuzz@e71e320

Signed-off-by: Paulo Gomes <paulo.gomes@weave.works>

tests/fuzz/Dockerfile.builder

@@ -3,9 +3,4 @@ FROM gcr.io/oss-fuzz-base/base-builder-go
 COPY ./ $GOPATH/src/github.com/fluxcd/helm-controller/
 COPY ./tests/fuzz/oss_fuzz_build.sh $SRC/build.sh
 
-# Temporarily overrides compile_native_go_fuzzer.
-# Pending upstream merge: https://github.com/google/oss-fuzz/pull/8285
-COPY tests/fuzz/compile_native_go_fuzzer.sh /usr/local/bin/compile_native_go_fuzzer
-RUN go install golang.org/x/tools/cmd/goimports@latest
-
 WORKDIR $SRC

tests/fuzz/oss_fuzz_build.sh

@@ -19,23 +19,61 @@ set -euxo pipefail
 GOPATH="${GOPATH:-/root/go}"
 GO_SRC="${GOPATH}/src"
 PROJECT_PATH="github.com/fluxcd/helm-controller"
+TMP_DIR=$(mktemp -d /tmp/oss_fuzz-XXXXXX)
+
+cleanup(){
+	rm -rf "${TMP_DIR}"
+}
+trap cleanup EXIT
+
+install_deps(){
+	if ! command -v go-118-fuzz-build &> /dev/null || ! command -v addimport &> /dev/null; then
+		mkdir -p "${TMP_DIR}/go-118-fuzz-build"
+
+		git clone https://github.com/AdamKorcz/go-118-fuzz-build "${TMP_DIR}/go-118-fuzz-build"
+		cd "${TMP_DIR}/go-118-fuzz-build"
+		go build -o "${GOPATH}/bin/go-118-fuzz-build"
+
+		cd addimport
+		go build -o "${GOPATH}/bin/addimport"
+	fi
+
+	if ! command -v goimports &> /dev/null; then
+		go install golang.org/x/tools/cmd/goimports@latest
+	fi
+}
+
+# Removes the content of test funcs which could cause the Fuzz
+# tests to break.
+remove_test_funcs(){
+	filename=$1
+
+	echo "removing co-located *testing.T"
+	sed -i -e '/func Test.*testing.T) {$/ {:r;/\n}/!{N;br}; s/\n.*\n/\n/}' "${filename}"
+
+	# After removing the body of the go testing funcs, consolidate the imports.
+	goimports -w "${filename}"
+}
+
+install_deps
 
 cd "${GO_SRC}/${PROJECT_PATH}"
 
-go install github.com/AdamKorcz/go-118-fuzz-build@latest
 go get github.com/AdamKorcz/go-118-fuzz-build/utils
 
 # Iterate through all Go Fuzz targets, compiling each into a fuzzer.
 test_files=$(grep -r --include='**_test.go' --files-with-matches 'func Fuzz' .)
 for file in ${test_files}
 do
+	remove_test_funcs "${file}"
+
 	targets=$(grep -oP 'func \K(Fuzz\w*)' "${file}")
 	for target_name in ${targets}
 	do
-        fuzzer_name=$(echo "${target_name}" | tr '[:upper:]' '[:lower:]')
-        target_dir=$(dirname "${file}")
+		fuzzer_name=$(echo "${target_name}" | tr '[:upper:]' '[:lower:]')
+		target_dir=$(dirname "${file}")
 
 		echo "Building ${file}.${target_name} into ${fuzzer_name}"
-        compile_native_go_fuzzer "${target_dir}" "${target_name}" "${fuzzer_name}" fuzz
+		compile_native_go_fuzzer "${target_dir}" "${target_name}" "${fuzzer_name}"
 	done
 done