linting: add shelcheck for shell script lint

Add linting for shell scripts in the scipts directory as well as any
*.sh file accross the project using shellcheck.

Signed-off-by: Andreas Hatziiliou <andreas.hatziiliou@savoirfairelinux.com>

Author: L-series

scripts/lint

@@ -106,6 +106,57 @@ gh_error_simple()
   fi
 }
 
+# Identify shell scripts that should be linted with shellcheck.
+shellcheck-targets()
+{
+  git ls-files -z -- "*.sh" "scripts/*" "scripts/**/*"
+}
+
+run-shellcheck()
+{
+  if ! command -v shellcheck >/dev/null; then
+    gh_error_simple "Shellcheck missing" "shellcheck is not installed"
+    error "Lint shellcheck"
+    SUCCESS=false
+    gh_summary_failure "Lint shellcheck"
+    return 0
+  fi
+
+  local file
+  local -a files=()
+  while IFS= read -r -d '' file; do
+    if [[ -L $file || ! -f $file ]]; then
+      continue
+    fi
+    case "$file" in
+      *.sh)
+        files+=("$file")
+        continue
+        ;;
+    esac
+    if head -n1 "$file" | grep -qE '^#!.*/(env )?(ba|da|k|mk|z|)sh'; then
+      files+=("$file")
+    fi
+  done < <(shellcheck-targets)
+
+  if [[ ${#files[@]} == 0 ]]; then
+    info "Lint shellcheck (no scripts)"
+    gh_summary_success "Lint shellcheck"
+    return 0
+  fi
+
+  local shellcheck_out
+  if ! shellcheck_out=$(shellcheck --format=gcc "${files[@]}" 2>&1); then
+    gh_error_simple "Shellcheck error" "$shellcheck_out"
+    error "Lint shellcheck"
+    SUCCESS=false
+    gh_summary_failure "Lint shellcheck"
+  else
+    info "Lint shellcheck"
+    gh_summary_success "Lint shellcheck"
+  fi
+}
+
 # Formatting
 SUCCESS=true
 
@@ -117,6 +168,10 @@ gh_group_start "Linting shell scripts with shfmt"
 checkerr "Lint shell" "$(shfmt -s -l -i 2 -ci -fn $(shfmt -f $(git grep -l '' :/)))"
 gh_group_end
 
+gh_group_start "Linting shell scripts with shellcheck"
+run-shellcheck
+gh_group_end
+
 gh_group_start "Linting python scripts with black"
 if ! diff=$(black --check --diff -q --include "(scripts/tests|scripts/simpasm|scripts/cfify|scripts/autogen|scripts/check-namespace|\.py$)" "$ROOT"); then
   gh_error_simple "Format error" "$diff"