stage_executor,getCreatedBy: expand buildArgs for sources correctly

Patch in PR #5691 added a
function to calculate and write checksum to history of `source` in
`--mount` instructions but it did not add part to expand build args if
they are present in `source` path.

Following PR Just corrects the above issue and also adds a new test to
make sure we don't break this in future again.

Closes: containers/podman#25425

Signed-off-by: flouthoc <[email protected]>

Author: flouthoc

imagebuildah/stage_executor.go

@@ -1896,6 +1896,10 @@ func (s *StageExecutor) getCreatedBy(node *parser.Node, addedContentSummary stri
 					continue
 				}
 				mountOptionSource = mountInfo.Source
+				mountOptionSource, err = imagebuilder.ProcessWord(mountOptionSource, s.stage.Builder.Arguments())
+				if err != nil {
+					return "", fmt.Errorf("getCreatedBy: while replacing arg variables with values for format %q: %w", mountOptionSource, err)
+				}
 				mountOptionFrom = mountInfo.From
 				// If source is not specified then default is '.'
 				if mountOptionSource == "" {

tests/bud.bats

@@ -6757,6 +6757,16 @@ _EOF
   expect_output --substring "hello"
 }
 
+@test "bud-with-mount-relative-path-like-buildkit-arg-in-source" {
+  skip_if_no_runtime
+  skip_if_in_container
+  _prefetch alpine
+  local contextdir=${TEST_SCRATCH_DIR}/buildkit-mount
+  cp -R $BUDFILES/buildkit-mount $contextdir
+  run_buildah build --build-arg INPUTPATH_1=subdir -t testbud $WITH_POLICY_JSON -f $contextdir/Containerfile5 $contextdir/
+  expect_output --substring "hello"
+}
+
 @test "bud-with-mount-with-rw-like-buildkit" {
   skip_if_no_runtime
   skip_if_in_container

tests/bud/buildkit-mount/Containerfile5

@@ -0,0 +1,5 @@
+FROM alpine
+ARG INPUTPATH_1=subdir
+RUN mkdir /test
+# use option z if selinux is enabled
+RUN --mount=type=bind,source=${INPUTPATH_1:?}/,target=/test,z cat /test/input_file