make: 'Makefile:12: *** missing separator. Stop.' What causes it and how do I fix the Makefile?

Cause: in a Makefile, every command line in a rule (the recipe) must start with a literal tab character. GNU make reports 'missing separator' when it finds a line it can't parse as a rule, variable assignment or directive; by far the most common reason is a recipe line indented with spaces instead of a tab. Editors that convert tabs to spaces, copying Makefiles from web pages or chat output, and AI-generated edits are typical sources. Other causes: a stray line without ':' or '=' (for example a command accidentally placed outside a rule), Windows CRLF line endings in some cases, or using syntax from another make (BSD make) in GNU make. Fix: 1. Go to the line number in the message and check its indentation: cat -A Makefile (or cat -et) shows tabs as ^I and line ends as $. Recipe lines must start with ^I, not spaces. 2. Replace the leading spaces with a single tab on each recipe line. In editors, disable 'insert spaces' for Makefiles (EditorConfig: [Makefile] indent_style = tab). 3. If you can't use tabs (generated files), GNU make lets you choose another recipe prefix with the .RECIPEPREFIX variable, e.g. .RECIPEPREFIX = > at the top, then start recipe lines with >. Use this sparingly, since it surprises other readers. 4. If the line isn't meant to be a recipe, fix its syntax: rules need 'target: prerequisites', assignments need '=' or ':='. 5. Convert CRLF to LF if the file came from Windows (dos2unix Makefile or your editor's line-ending setting). Verify: make -n (dry run) parses the file and prints the commands it would run without errors. Sources: https://www.gnu.org/software/make/manual/html_node/Error-Messages.html https://www.gnu.org/software/make/manual/html_node/Rule-Syntax.html