Array data source in the path of another can result in golang Panic

[vassudanagunta]

When two source data files at the same level in the Site.Data tree contain array data at the top level, such as the following:

themes/mytheme/data/a/b1.json:

["x", "y", "z"]

data/a/b1.json:

["1", "2", "3"]

...the following error occurs:

PANIC: interface conversion: interface {} is []interface {}, not map[string]interface {}

The expected behavior is that Site.Data.a.b1 = ["1", "2", "3"]

The culprit is the Site.handleDataFile(...) in site.go, in which the following section of code checks for pre-existing data at a node in the tree and incorrectly assumes it is a map node:

hugo/hugolib/site.go

Lines 815 to 817 in 19e26cb

	// Copy content from current to data when needed
	if _, ok := current[r.BaseFileName()]; ok {
	data := data.(map[string]interface{})

This is a pre-existing bug that goes back to at least 2015.

Add the following test to datafiles_test.go to uncover (and cover) this case:

func TestDataDirMultipleSourcesArrayFile(t *testing.T) {
	t.Parallel()

	sources := [][2]string{
		{filepath.FromSlash("themes/mytheme/data/a/b1.json"), `["x", "y", "z"]`},
		{filepath.FromSlash("data/a/b1.json"), `["1", "2", "3"]`},
	}

	// Per handleDataFile() comment:
	// 1. A theme uses the same key; the main data folder wins
	// 2. A sub folder uses the same key: the sub folder wins
	expected, err := parser.HandleJSONMetaData([]byte(`
{ "a" : {
        "b1": ["1", "2", "3"]
        }
}`))

	if err != nil {
		t.Errorf("Error %s", err)
		return
	}

	doTestDataDir(t, expected, sources,
		"theme", "mytheme")
}

(bug uncovered while investigating #4361.

[github-actions]

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