Default values may reference earlier parameters

src/recipe_resolver.rs

@@ -23,10 +23,10 @@ impl<'src: 'run, 'run> RecipeResolver<'src, 'run> {
     }
 
     for recipe in resolver.resolved_recipes.values() {
-      for parameter in &recipe.parameters {
+      for (i, parameter) in recipe.parameters.iter().enumerate() {
         if let Some(expression) = &parameter.default {
           for variable in expression.variables() {
-            resolver.resolve_variable(&variable, &[])?;
+            resolver.resolve_variable(&variable, &recipe.parameters[..i])?;
           }
         }
       }
@@ -63,11 +63,12 @@ impl<'src: 'run, 'run> RecipeResolver<'src, 'run> {
     parameters: &[Parameter],
   ) -> CompileResult<'src> {
     let name = variable.lexeme();
-    let undefined = !self.assignments.contains_key(name)
-      && !parameters.iter().any(|p| p.name.lexeme() == name)
-      && !constants().contains_key(name);
 
-    if undefined {
+    let defined = self.assignments.contains_key(name)
+      || parameters.iter().any(|p| p.name.lexeme() == name)
+      || constants().contains_key(name);
+
+    if !defined {
       return Err(variable.error(UndefinedVariable { variable: name }));
     }
 

tests/lib.rs

@@ -82,6 +82,7 @@ mod no_cd;
 mod no_dependencies;
 mod no_exit_message;
 mod os_attributes;
+mod parameters;
 mod parser;
 mod positional_arguments;
 mod private;

tests/misc.rs

@@ -1941,26 +1941,6 @@ test! {
   shell: false,
 }
 
-test! {
-  name: parameter_cross_reference_error,
-  justfile: "
-    foo:
-
-    bar a b=a:
-  ",
-  args: (),
-  stdout: "",
-  stderr: "
-    error: Variable `a` not defined
-     ——▶ justfile:3:9
-      │
-    3 │ bar a b=a:
-      │         ^
-  ",
-  status: EXIT_FAILURE,
-  shell: false,
-}
-
 #[cfg(windows)]
 test! {
   name: pwsh_invocation_directory,

tests/parameters.rs

@@ -0,0 +1,38 @@
+use super::*;
+
+#[test]
+fn parameter_default_values_may_use_earlier_parameters() {
+  Test::new()
+    .justfile(
+      "
+        @foo a b=a:
+          echo {{ b }}
+      ",
+    )
+    .args(["foo", "bar"])
+    .stdout("bar\n")
+    .run();
+}
+
+#[test]
+fn parameter_default_values_may_not_use_later_parameters() {
+  Test::new()
+    .justfile(
+      "
+        @foo a b=c c='':
+          echo {{ b }}
+      ",
+    )
+    .args(["foo", "bar"])
+    .stderr(
+      "
+        error: Variable `c` not defined
+         ——▶ justfile:1:10
+          │
+        1 │ @foo a b=c c='':
+          │          ^
+      ",
+    )
+    .status(EXIT_FAILURE)
+    .run();
+}