Fix inverted logic in quarto.utils.is_empty_node for text nodes

The text branch (`node.text`) used `~=` (not-equal) where it should
use `==` (equal), causing is_empty_node to return true for non-empty
text nodes and false for empty ones.

Text nodes like Str and Code should follow the same emptiness
semantics as container nodes like Para and Div: a Str('') is empty
just as Para({}) is empty -- a node of the right type but with
nothing in it.

Internal callers all pass container nodes (caption, preamble) so
nothing was visibly broken, but extension authors calling the public
API on text nodes get wrong results.

Author: cderv

src/resources/pandoc/datadir/_utils.lua

@@ -592,7 +592,7 @@ local function is_empty_node (node)
     return not next(node.caption)
   elseif node.text then
     -- looks like a code node or text node
-    return node.text ~= ''
+    return node.text == ''
   else
     -- Not sure what this is, but it's probably not empty.
     return false

tests/docs/smoke-all/lua/quarto-utils-is-empty-node/test.lua

@@ -0,0 +1,26 @@
+function Pandoc(doc)
+  local is_empty = quarto.utils.is_empty_node
+
+  -- nil is empty
+  assert(is_empty(nil) == true, "nil should be empty")
+
+  -- text nodes: Str
+  assert(is_empty(pandoc.Str("")) == true, "Str('') should be empty")
+  assert(is_empty(pandoc.Str("hello")) == false, "Str('hello') should not be empty")
+
+  -- text nodes: Code
+  assert(is_empty(pandoc.Code("")) == true, "Code('') should be empty")
+  assert(is_empty(pandoc.Code("x")) == false, "Code('x') should not be empty")
+
+  -- text nodes: RawInline
+  assert(is_empty(pandoc.RawInline("html", "")) == true, "RawInline('') should be empty")
+  assert(is_empty(pandoc.RawInline("html", "<br>")) == false, "RawInline('<br>') should not be empty")
+
+  -- container nodes: empty vs non-empty
+  assert(is_empty(pandoc.Para({})) == true, "Para({}) should be empty")
+  assert(is_empty(pandoc.Para({pandoc.Str("hi")})) == false, "Para with content should not be empty")
+
+  -- empty table
+  assert(is_empty({}) == true, "empty table should be empty")
+  assert(is_empty({1}) == false, "non-empty table should not be empty")
+end

tests/docs/smoke-all/lua/quarto-utils-is-empty-node/test.qmd

@@ -0,0 +1,7 @@
+---
+title: is_empty_node tests
+filters:
+  - test.lua
+---
+
+Some content.