Add modules

README.md

@@ -2329,7 +2329,7 @@ And will both invoke recipes `a` and `b` in `foo/justfile`.
 
 ### Imports
 
-One `justfile` can include the contents of another using an `import` statement.
+One `justfile` can include the contents of another using `import` statements.
 
 If you have the following `justfile`:
 
@@ -2366,6 +2366,51 @@ and recipes defined after the `import` statement.
 Imported files can themselves contain `import`s, which are processed
 recursively.
 
+### Modules<sup>master</sup>
+
+A `justfile` can declare modules using `mod` statements. `mod` statements are
+currently unstable, so you'll need to use the `--unstable` flag, or set the
+`JUST_UNSTABLE` environment variable to use them.
+
+If you have the following `justfile`:
+
+```mf
+mod bar
+
+a:
+  @echo A
+```
+
+And the following text in `bar.just`:
+
+```just
+b:
+  @echo B
+```
+
+`bar.just` will be included in `justfile` as a submodule. Recipes, aliases, and
+variables defined in one submodule cannot be used in another, and each module
+uses its own settings.
+
+Recipes in submodules can be invoked as subcommands:
+
+```sh
+$ just --unstable bar b
+B
+```
+
+If a module is named `foo`, just will search for the module file in `foo.just`,
+`foo/mod.just`, `foo/justfile`, and `foo/.justfile`. In the latter two cases,
+the module file may have any capitalization.
+
+Environment files are loaded for the root justfile.
+
+Currently, recipes in submodules run with the same working directory as the
+root `justfile`, and the `justfile()` and `justfile_directory()` functions
+return the path to the root `justfile` and its parent directory.
+
+See the [module stabilization tracking issue](https://github.com/casey/just/issues/929) for more information.
+
 ### Hiding `justfile`s
 
 `just` looks for `justfile`s named `justfile` and `.justfile`, which can be used to keep a `justfile` hidden.

src/alias.rs

@@ -13,10 +13,6 @@ pub(crate) struct Alias<'src, T = Rc<Recipe<'src>>> {
 }
 
 impl<'src> Alias<'src, Name<'src>> {
-  pub(crate) fn line_number(&self) -> usize {
-    self.name.line
-  }
-
   pub(crate) fn resolve(self, target: Rc<Recipe<'src>>) -> Alias<'src> {
     assert_eq!(self.target.lexeme(), target.name.lexeme());
 

src/analyzer.rs

@@ -9,7 +9,7 @@ pub(crate) struct Analyzer<'src> {
 
 impl<'src> Analyzer<'src> {
   pub(crate) fn analyze(
-    loaded: Vec<PathBuf>,
+    loaded: &[PathBuf],
     paths: &HashMap<PathBuf, PathBuf>,
     asts: &HashMap<PathBuf, Ast<'src>>,
     root: &Path,
@@ -19,7 +19,7 @@ impl<'src> Analyzer<'src> {
 
   fn justfile(
     mut self,
-    loaded: Vec<PathBuf>,
+    loaded: &[PathBuf],
     paths: &HashMap<PathBuf, PathBuf>,
     asts: &HashMap<PathBuf, Ast<'src>>,
     root: &Path,
@@ -31,18 +31,62 @@ impl<'src> Analyzer<'src> {
 
     let mut warnings = Vec::new();
 
+    let mut modules: BTreeMap<String, (Name, Justfile)> = BTreeMap::new();
+
+    let mut definitions: HashMap<&str, (&'static str, Name)> = HashMap::new();
+
+    let mut define = |name: Name<'src>,
+                      second_type: &'static str,
+                      duplicates_allowed: bool|
+     -> CompileResult<'src, ()> {
+      if let Some((first_type, original)) = definitions.get(name.lexeme()) {
+        if !(*first_type == second_type && duplicates_allowed) {
+          let (original, redefinition) = if name.line < original.line {
+            (name, *original)
+          } else {
+            (*original, name)
+          };
+
+          return Err(redefinition.token().error(Redefinition {
+            first_type,
+            second_type,
+            name: name.lexeme(),
+            first: original.line,
+          }));
+        }
+      }
+
+      definitions.insert(name.lexeme(), (second_type, name));
+
+      Ok(())
+    };
+
     while let Some(ast) = stack.pop() {
       for item in &ast.items {
         match item {
           Item::Alias(alias) => {
-            self.analyze_alias(alias)?;
+            define(alias.name, "alias", false)?;
+            Self::analyze_alias(alias)?;
             self.aliases.insert(alias.clone());
           }
           Item::Assignment(assignment) => {
             self.analyze_assignment(assignment)?;
             self.assignments.insert(assignment.clone());
           }
           Item::Comment(_) => (),
+          Item::Import { absolute, .. } => {
+            stack.push(asts.get(absolute.as_ref().unwrap()).unwrap());
+          }
+          Item::Mod { absolute, name } => {
+            define(*name, "module", false)?;
+            modules.insert(
+              name.to_string(),
+              (
+                *name,
+                Self::analyze(loaded, paths, asts, absolute.as_ref().unwrap())?,
+              ),
+            );
+          }
           Item::Recipe(recipe) => {
             if recipe.enabled() {
               Self::analyze_recipe(recipe)?;
@@ -53,9 +97,6 @@ impl<'src> Analyzer<'src> {
             self.analyze_set(set)?;
             self.sets.insert(set.clone());
           }
-          Item::Import { absolute, .. } => {
-            stack.push(asts.get(absolute.as_ref().unwrap()).unwrap());
-          }
         }
       }
 
@@ -69,14 +110,7 @@ impl<'src> Analyzer<'src> {
     AssignmentResolver::resolve_assignments(&self.assignments)?;
 
     for recipe in recipes {
-      if let Some(original) = recipe_table.get(recipe.name.lexeme()) {
-        if !settings.allow_duplicate_recipes {
-          return Err(recipe.name.token().error(DuplicateRecipe {
-            recipe: original.name(),
-            first: original.line_number(),
-          }));
-        }
-      }
+      define(recipe.name, "recipe", settings.allow_duplicate_recipes)?;
       recipe_table.insert(recipe.clone());
     }
 
@@ -103,10 +137,14 @@ impl<'src> Analyzer<'src> {
         }),
       aliases,
       assignments: self.assignments,
-      loaded,
+      loaded: loaded.into(),
       recipes,
       settings,
       warnings,
+      modules: modules
+        .into_iter()
+        .map(|(name, (_name, justfile))| (name, justfile))
+        .collect(),
     })
   }
 
@@ -164,16 +202,9 @@ impl<'src> Analyzer<'src> {
     Ok(())
   }
 
-  fn analyze_alias(&self, alias: &Alias<'src, Name<'src>>) -> CompileResult<'src, ()> {
+  fn analyze_alias(alias: &Alias<'src, Name<'src>>) -> CompileResult<'src, ()> {
     let name = alias.name.lexeme();
 
-    if let Some(original) = self.aliases.get(name) {
-      return Err(alias.name.token().error(DuplicateAlias {
-        alias: name,
-        first: original.line_number(),
-      }));
-    }
-
     for attr in &alias.attributes {
       if *attr != Attribute::Private {
         return Err(alias.name.token().error(AliasInvalidAttribute {
@@ -232,7 +263,7 @@ mod tests {
     line: 1,
     column: 6,
     width: 3,
-    kind: DuplicateAlias { alias: "foo", first: 0 },
+    kind: Redefinition { first_type: "alias", second_type: "alias", name: "foo", first: 0 },
   }
 
   analysis_error! {
@@ -248,11 +279,11 @@ mod tests {
   analysis_error! {
     name: alias_shadows_recipe_before,
     input: "bar: \n  echo bar\nalias foo := bar\nfoo:\n  echo foo",
-    offset: 23,
-    line: 2,
-    column: 6,
+    offset: 34,
+    line: 3,
+    column: 0,
     width: 3,
-    kind: AliasShadowsRecipe {alias: "foo", recipe_line: 3},
+    kind: Redefinition { first_type: "alias", second_type: "recipe", name: "foo", first: 2 },
   }
 
   analysis_error! {
@@ -262,7 +293,7 @@ mod tests {
     line: 2,
     column: 6,
     width: 3,
-    kind: AliasShadowsRecipe { alias: "foo", recipe_line: 0 },
+    kind: Redefinition { first_type: "alias", second_type: "recipe", name: "foo", first: 0 },
   }
 
   analysis_error! {
@@ -302,7 +333,7 @@ mod tests {
     line:   2,
     column: 0,
     width:  1,
-    kind:   DuplicateRecipe{recipe: "a", first: 0},
+    kind:   Redefinition { first_type: "recipe", second_type: "recipe", name: "a", first: 0 },
   }
 
   analysis_error! {

src/compile_error.rs

@@ -19,6 +19,14 @@ impl<'src> CompileError<'src> {
   }
 }
 
+fn capitalize(s: &str) -> String {
+  let mut chars = s.chars();
+  match chars.next() {
+    None => String::new(),
+    Some(first) => first.to_uppercase().collect::<String>() + chars.as_str(),
+  }
+}
+
 impl Display for CompileError<'_> {
   fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
     use CompileErrorKind::*;
@@ -82,12 +90,6 @@ impl Display for CompileError<'_> {
           write!(f, "at most {max} {}", Count("argument", *max))
         }
       }
-      DuplicateAlias { alias, first } => write!(
-        f,
-        "Alias `{alias}` first defined on line {} is redefined on line {}",
-        first.ordinal(),
-        self.token.line.ordinal(),
-      ),
       DuplicateAttribute { attribute, first } => write!(
         f,
         "Recipe attribute `{attribute}` first used on line {} is duplicated on line {}",
@@ -97,12 +99,6 @@ impl Display for CompileError<'_> {
       DuplicateParameter { recipe, parameter } => {
         write!(f, "Recipe `{recipe}` has duplicate parameter `{parameter}`")
       }
-      DuplicateRecipe { recipe, first } => write!(
-        f,
-        "Recipe `{recipe}` first defined on line {} is redefined on line {}",
-        first.ordinal(),
-        self.token.line.ordinal(),
-      ),
       DuplicateSet { setting, first } => write!(
         f,
         "Setting `{setting}` first set on line {} is redefined on line {}",
@@ -183,6 +179,31 @@ impl Display for CompileError<'_> {
         write!(f, "Parameter `{parameter}` follows variadic parameter")
       }
       ParsingRecursionDepthExceeded => write!(f, "Parsing recursion depth exceeded"),
+      Redefinition {
+        first,
+        first_type,
+        name,
+        second_type,
+      } => {
+        if first_type == second_type {
+          write!(
+            f,
+            "{} `{name}` first defined on line {} is redefined on line {}",
+            capitalize(first_type),
+            first.ordinal(),
+            self.token.line.ordinal(),
+          )
+        } else {
+          write!(
+            f,
+            "{} `{name}` defined on line {} is redefined as {} {second_type} on line {}",
+            capitalize(first_type),
+            first.ordinal(),
+            if *second_type == "alias" { "an" } else { "a" },
+            self.token.line.ordinal(),
+          )
+        }
+      }
       RequiredParameterFollowsDefaultParameter { parameter } => write!(
         f,
         "Non-default parameter `{parameter}` follows default parameter"

src/compile_error_kind.rs

@@ -25,9 +25,11 @@ pub(crate) enum CompileErrorKind<'src> {
     min: usize,
     max: usize,
   },
-  DuplicateAlias {
-    alias: &'src str,
+  Redefinition {
     first: usize,
+    first_type: &'static str,
+    name: &'src str,
+    second_type: &'static str,
   },
   DuplicateAttribute {
     attribute: &'src str,
@@ -37,10 +39,6 @@ pub(crate) enum CompileErrorKind<'src> {
     recipe: &'src str,
     parameter: &'src str,
   },
-  DuplicateRecipe {
-    recipe: &'src str,
-    first: usize,
-  },
   DuplicateSet {
     setting: &'src str,
     first: usize,