Warn if parsed and raw outputs mismatch

conda_build/metadata.py

@@ -2228,6 +2228,15 @@ def extract_single_output_text(
         if not outputs:
             outputs = [{"name": self.name()}]
 
+        if len(output_matches) != len(outputs):
+            # See https://github.com/conda/conda-build/issues/5571
+            utils.get_logger(__name__).warning(
+                "Number of parsed outputs does not match detected raw metadata blocks. "
+                "Identified output block may be wrong! "
+                "If you are using Jinja conditionals to include or exclude outputs, "
+                "consider using `skip: true  # [condition]` instead."
+            )
+
         try:
             if output_type:
                 output_tuples = [
@@ -2250,7 +2259,8 @@ def extract_single_output_text(
         except ValueError:
             if not self.path and self.meta.get("extra", {}).get("parent_recipe"):
                 utils.get_logger(__name__).warning(
-                    f"Didn't match any output in raw metadata.  Target value was: {output_name}"
+                    "Didn't match any output in raw metadata. Target value was: %s",
+                    output_name,
                 )
                 output = ""
             else:

news/5601-warn-mismatches

@@ -0,0 +1,19 @@
+### Enhancements
+
+* <news item>
+
+### Bug fixes
+
+* Warn about parsed and raw output block mismatches. This can cause issues with custom build strings, among others. The recommendation is to avoid Jinja flow control to build the output list. Use `skip: true` as necessary. (#5571 via #5601)
+
+### Deprecations
+
+* <news item>
+
+### Docs
+
+* <news item>
+
+### Other
+
+* <news item>