Makefile Tab Indentation Rule

This rule applies to files matching the patterns above.

# Makefile Tab Indentation Rule

## Rule
All Makefile recipe lines (commands under targets) MUST use tab characters for indentation. Spaces cause a syntax error. Configure editors to use tabs in Makefiles.

## Why
GNU Make requires literal tab characters before recipe lines. This is a syntactic requirement from 1976 that cannot be changed. Spaces produce the cryptic error: `*** missing separator. Stop.`

## Format
```makefile
# CORRECT: tab-indented recipe
.PHONY: build
build:
	go build -o bin/app ./cmd/app
↑ This MUST be a tab character

# WRONG: space-indented recipe
.PHONY: build
build:
    go build -o bin/app ./cmd/app
↑ These spaces cause: *** missing separator. Stop.
```

## Editor Configuration

### VS Code
```json
// .vscode/settings.json
{
  "[makefile]": {
    "editor.insertSpaces": false,
    "editor.tabSize": 4
  }
}
```

### .editorconfig
```ini
[Makefile]
indent_style = tab
indent_size = 4

[*.mk]
indent_style = tab
indent_size = 4
```

### Neovim
```lua
vim.api.nvim_create_autocmd("FileType", {
  pattern = "make",
  callback = function()
    vim.opt_local.expandtab = false
    vim.opt_local.tabstop = 4
  end,
})
```

## Debugging
```bash
# Check for spaces in Makefile
cat -A Makefile | grep "^    "
# ^I = tab (correct), spaces = wrong

# Show invisible characters
cat -et Makefile
```

## Good
```
build:
^Igo build -o bin/app    (^I = tab character)
```

## Bad
```
build:
    go build -o bin/app    (4 spaces = syntax error)
```