Display a descriptive error for !include directives (#1779)

src/compile_error.rs

@@ -135,6 +135,10 @@ impl Display for CompileError<'_> {
         Count("argument", *found),
         expected.display(),
       ),
+      Include => write!(
+        f,
+        "The `!include` directive has been stabilized as `import`"
+      ),
       InconsistentLeadingWhitespace { expected, found } => write!(
         f,
         "Recipe line has inconsistent leading whitespace. Recipe started with `{}` but found \

src/compile_error_kind.rs

@@ -58,6 +58,7 @@ pub(crate) enum CompileErrorKind<'src> {
     found: usize,
     expected: Range<usize>,
   },
+  Include,
   InconsistentLeadingWhitespace {
     expected: &'src str,
     found: &'src str,

src/lexer.rs

@@ -481,6 +481,7 @@ impl<'src> Lexer<'src> {
   fn lex_normal(&mut self, start: char) -> CompileResult<'src, ()> {
     match start {
       ' ' | '\t' => self.lex_whitespace(),
+      '!' if self.rest().starts_with("!include") => Err(self.error(Include)),
       '!' => self.lex_digraph('!', '=', BangEquals),
       '#' => self.lex_comment(),
       '$' => self.lex_single(Dollar),

tests/imports.rs

@@ -110,3 +110,20 @@ fn listed_recipes_in_imports_are_in_load_order() {
     )
     .run();
 }
+
+#[test]
+fn include_error() {
+  Test::new()
+    .justfile("!include foo")
+    .status(EXIT_FAILURE)
+    .stderr(
+      "
+      error: The `!include` directive has been stabilized as `import`
+       --> justfile:1:1
+        |
+      1 | !include foo
+        | ^
+      ",
+    )
+    .run();
+}