docs: suggest setting fetch-depth on ref errors (#5316)

Emit a hopefully more helpful error message when the Git ref doesn't
exist. The error message is the same we use when getting changed files
only: it suggests checking that repository clone is not shallow, and
that the full history is available. Additionally, when running on
GitHub Actions, it also suggests checking the fetch-depth option of the
actions/checkout step.

Fix #5315

lib/functions/buildFileList.sh

@@ -8,6 +8,7 @@ function IssueHintForFullGitHistory() {
   info "See https://github.com/super-linter/super-linter#get-started"
   info "Is shallow repository: $(git -C "${GITHUB_WORKSPACE}" rev-parse --is-shallow-repository)"
 }
+export -f IssueHintForFullGitHistory
 
 function GenerateFileDiff() {
   local DIFF_GIT_DEFAULT_BRANCH_CMD

lib/functions/validation.sh

@@ -200,6 +200,7 @@ function ValidateGitShaReference() {
 
   debug "Validate that the GITHUB_SHA reference (${GITHUB_SHA}) exists in this Git repository."
   if ! CheckIfGitRefExists "${GITHUB_SHA}"; then
+    IssueHintForFullGitHistory
     fatal "The GITHUB_SHA reference (${GITHUB_SHA}) doesn't exist in this Git repository"
   else
     debug "The GITHUB_SHA reference (${GITHUB_SHA}) exists in this repository"