fine/build.rs

@@ -17,7 +17,7 @@ fn generate_test_for_file(path: PathBuf) -> String {
         };
 
         let line = line.trim();
-        if line == "@concrete:" {
+        if line == "concrete:" {
             let mut concrete = String::new();
             while let Some(line) = lines.next() {
                 let line = match line.strip_prefix("// | ") {
@@ -32,7 +32,7 @@ fn generate_test_for_file(path: PathBuf) -> String {
             assertions.push(quote! {
                 crate::assert_concrete(&_tree, #concrete, #display_path);
             });
-        } else if let Some(line) = line.strip_prefix("@type:") {
+        } else if let Some(line) = line.strip_prefix("type:") {
             let (pos, expected) = line
                 .trim()
                 .split_once(' ')
@@ -45,7 +45,7 @@ fn generate_test_for_file(path: PathBuf) -> String {
             assertions.push(quote! {
                 crate::assert_type_at(&_tree, &_lines, #pos, #expected, #display_path);
             });
-        } else if let Some(line) = line.strip_prefix("@type-error:") {
+        } else if let Some(line) = line.strip_prefix("type-error:") {
             let (pos, expected) = line
                 .trim()
                 .split_once(' ')

fine/src/main.rs

@@ -18,7 +18,7 @@ pub fn process_file(file: &str) {
 
     // This is... probably wrong, I don't know, what am I doing?
     for t in tree.trees() {
-        let _ = semantics.type_of(t);
+        let _ = semantics.type_of(t, false);
     }
 
     // OK now there might be errors.

fine/src/semantics.rs

@@ -90,7 +90,6 @@ impl Type {
             (Type::String, Type::String) => true,
             (Type::Bool, Type::Bool) => true,
             (Type::Unreachable, Type::Unreachable) => true,
-            (Type::Nothing, Type::Nothing) => true,
 
             // Avoid introducing more errors
             (Type::Error, _) => true,
@@ -127,7 +126,7 @@ pub struct Semantics<'a> {
     syntax_tree: &'a SyntaxTree<'a>,
     lines: &'a Lines,
     errors: RefCell<Vec<Error>>,
-    types: RefCell<HashMap<TreeRef, Type>>,
+    types: RefCell<HashMap<(TreeRef, bool), Type>>,
 }
 
 impl<'a> Semantics<'a> {
@@ -210,27 +209,29 @@ impl<'a> Semantics<'a> {
         }
     }
 
-    pub fn type_of(&self, t: TreeRef) -> Option<Type> {
-        if let Some(existing) = self.types.borrow().get(&t) {
+    pub fn type_of(&self, t: TreeRef, value_required: bool) -> Option<Type> {
+        if let Some(existing) = self.types.borrow().get(&(t, value_required)) {
             return Some(existing.clone());
         }
 
         let tree = &self.syntax_tree[t];
         let result = match tree.kind {
             TreeKind::Error => Some(Type::Error),
-            TreeKind::UnaryExpression => self.type_of_unary(tree),
-            TreeKind::BinaryExpression => self.type_of_binary(tree),
-            TreeKind::TypeExpression => self.type_of_type_expr(tree),
-            TreeKind::Block => self.type_of_block(tree),
+            TreeKind::UnaryExpression => self.type_of_unary(tree, value_required),
+            TreeKind::BinaryExpression => self.type_of_binary(tree, value_required),
+            TreeKind::TypeExpression => self.type_of_type_expr(tree, value_required),
+            TreeKind::Block => self.type_of_block(tree, value_required),
             TreeKind::LiteralExpression => self.type_of_literal(tree),
-            TreeKind::GroupingExpression => self.type_of_grouping(tree),
-            TreeKind::ConditionalExpression => self.type_of_conditional(tree),
+            TreeKind::GroupingExpression => self.type_of_grouping(tree, value_required),
+            TreeKind::ConditionalExpression => self.type_of_conditional(tree, value_required),
             TreeKind::CallExpression => self.type_of_call(tree),
             TreeKind::Argument => self.type_of_argument(tree),
 
             TreeKind::LetStatement => Some(Type::Nothing),
             TreeKind::ReturnStatement => Some(Type::Unreachable),
-            TreeKind::ExpressionStatement => self.type_of_expression_statement(tree),
+            TreeKind::ExpressionStatement => {
+                self.type_of_expression_statement(tree, value_required)
+            }
             TreeKind::Identifier => self.type_of_identifier(tree),
             _ => return None,
         };
@@ -238,18 +239,20 @@ impl<'a> Semantics<'a> {
         // NOTE: These return `None` if they encounter some problem.
         let result = result.unwrap_or(Type::Error);
 
-        self.types.borrow_mut().insert(t, result.clone());
+        self.types
+            .borrow_mut()
+            .insert((t, value_required), result.clone());
         Some(result)
     }
 
-    fn type_of_unary(&self, tree: &Tree) -> Option<Type> {
+    fn type_of_unary(&self, tree: &Tree, value_required: bool) -> Option<Type> {
         assert_eq!(tree.kind, TreeKind::UnaryExpression);
 
         let op = tree.nth_token(0)?;
         let expr = tree.nth_tree(1)?;
 
         let argument_type = self
-            .type_of(expr)
+            .type_of(expr, value_required)
             .expect("Our argument should be an expression");
 
         match (op.kind, argument_type) {
@@ -283,14 +286,14 @@ impl<'a> Semantics<'a> {
         }
     }
 
-    fn type_of_binary(&self, tree: &Tree) -> Option<Type> {
+    fn type_of_binary(&self, tree: &Tree, value_required: bool) -> Option<Type> {
         assert_eq!(tree.kind, TreeKind::BinaryExpression);
         let lhs = self
-            .type_of(tree.nth_tree(0)?)
+            .type_of(tree.nth_tree(0)?, value_required)
             .expect("must be an expression");
         let op = tree.nth_token(1)?;
         let rhs = self
-            .type_of(tree.nth_tree(2)?)
+            .type_of(tree.nth_tree(2)?, value_required)
             .expect("must be an expression");
 
         match (op.kind, lhs, rhs) {
@@ -335,12 +338,12 @@ impl<'a> Semantics<'a> {
         }
     }
 
-    fn type_of_type_expr(&self, tree: &Tree) -> Option<Type> {
+    fn type_of_type_expr(&self, tree: &Tree, _value_required: bool) -> Option<Type> {
         assert_eq!(tree.kind, TreeKind::TypeExpression);
         Some(Type::Error)
     }
 
-    fn type_of_block(&self, tree: &Tree) -> Option<Type> {
+    fn type_of_block(&self, tree: &Tree, value_required: bool) -> Option<Type> {
         assert_eq!(tree.kind, TreeKind::Block);
 
         if tree.children.len() < 2 {
@@ -360,7 +363,7 @@ impl<'a> Semantics<'a> {
         let mut is_unreachable = false;
         for i in 1..last_index {
             is_unreachable = self
-                .type_of(tree.nth_tree(i)?)
+                .type_of(tree.nth_tree(i)?, false)
                 .map(|t| matches!(t, Type::Unreachable))
                 .unwrap_or(false)
                 || is_unreachable;
@@ -371,7 +374,7 @@ impl<'a> Semantics<'a> {
         //       (And explicitly not Error, which is what returning None
         //       would yield.)
         let last_type = self
-            .type_of(tree.nth_tree(last_index)?)
+            .type_of(tree.nth_tree(last_index)?, value_required)
             .unwrap_or(Type::Nothing);
 
         // If anything in this block generated an "Unreachable" then the
@@ -396,29 +399,34 @@ impl<'a> Semantics<'a> {
         Some(pig)
     }
 
-    fn type_of_grouping(&self, tree: &Tree) -> Option<Type> {
+    fn type_of_grouping(&self, tree: &Tree, value_required: bool) -> Option<Type> {
         assert_eq!(tree.kind, TreeKind::GroupingExpression);
 
         let expr = tree.nth_tree(1)?;
         Some(
-            self.type_of(expr)
+            self.type_of(expr, value_required)
                 .expect("the thing in the parenthesis must have some type"),
         )
     }
 
-    fn type_of_conditional(&self, tree: &Tree) -> Option<Type> {
+    fn type_of_conditional(&self, tree: &Tree, value_required: bool) -> Option<Type> {
         assert_eq!(tree.kind, TreeKind::ConditionalExpression);
 
         let cond_tree = tree.nth_tree(1)?;
-        let cond_type = self.type_of(cond_tree).expect("must be expression");
-        let then_type = self.type_of(tree.nth_tree(2)?).expect("must be expression");
+        let cond_type = self.type_of(cond_tree, true).expect("must be expression");
+        let then_type = self
+            .type_of(tree.nth_tree(2)?, value_required)
+            .expect("must be expression");
 
         let has_else = tree
             .nth_token(3)
             .map(|t| t.kind == TokenKind::Else)
             .unwrap_or(false);
         let else_type = if has_else {
-            Some(self.type_of(tree.nth_tree(4)?).expect("must be expression"))
+            Some(
+                self.type_of(tree.nth_tree(4)?, value_required)
+                    .expect("must be expression"),
+            )
         } else {
             None
         };
@@ -432,14 +440,23 @@ impl<'a> Semantics<'a> {
             match (then_type, else_type) {
                 (Type::Error, _) => Some(Type::Error),
                 (_, Some(Type::Error)) => Some(Type::Error),
-
-                (Type::Unreachable, None) => Some(Type::Unreachable),
-                (Type::Unreachable, Some(t)) => Some(t),
-                (t, Some(Type::Unreachable)) => Some(t),
-
-                (then_type, else_type) => {
-                    let else_type = else_type.unwrap_or(Type::Nothing);
-                    if !then_type.compatible_with(&else_type) {
+                (_, None) if value_required => {
+                    self.report_error_tree(
+                        tree,
+                        "this conditional expression needs an else arm to produce a value",
+                    );
+                    Some(Type::Error)
+                }
+                (then_type, Some(else_type)) if value_required => {
+                    if else_type.compatible_with(&Type::Unreachable) {
+                        // Doesn't matter if the value is required; the else branch
+                        // will never generate a value for us so let's ignore it.
+                        Some(then_type)
+                    } else if then_type.compatible_with(&Type::Unreachable) {
+                        // Or the then branch is unreachable, same thing with else
+                        // then.
+                        Some(else_type)
+                    } else if !then_type.compatible_with(&else_type) {
                         self.report_error_tree(
                             tree,
                             format!("the type of the `then` branch ({then_type}) must match the type of the `else` branch ({else_type})"),
@@ -449,6 +466,10 @@ impl<'a> Semantics<'a> {
                         Some(then_type)
                     }
                 }
+                (_, _) => {
+                    assert!(!value_required);
+                    Some(Type::Unreachable)
+                }
             }
         }
     }
@@ -463,20 +484,22 @@ impl<'a> Semantics<'a> {
         Some(Type::Error)
     }
 
-    fn type_of_expression_statement(&self, tree: &Tree) -> Option<Type> {
+    fn type_of_expression_statement(&self, tree: &Tree, value_required: bool) -> Option<Type> {
         assert_eq!(tree.kind, TreeKind::ExpressionStatement);
         let last_is_semicolon = tree
             .nth_token(tree.children.len() - 1)
             .map(|t| t.kind == TokenKind::Semicolon)
             .unwrap_or(false);
 
-        let expression_type = self.type_of(tree.nth_tree(0)?).expect("must be expression");
+        let expression_type = self
+            .type_of(tree.nth_tree(0)?, value_required && !last_is_semicolon)
+            .expect("must be expression");
         Some(match expression_type {
+            Type::Error => Type::Error,
             Type::Unreachable => Type::Unreachable,
             _ => {
                 // A semicolon at the end of an expression statement discards
-                // the value, leaving us with nothing. (Even if the
-                // expression otherwise generated a type error!)
+                // the value, leaving us with nothing.
                 if last_is_semicolon {
                     Type::Nothing
                 } else {

fine/tests/README.md

@@ -1,79 +0,0 @@
-# Snapshot Tests
-
-The `.fine` files in this directory and its descendants are processed
-by `build.rs` into a series of snapshot-tests. The various test
-assertions are specified by `@` directives in comments in the file.
-
-e.g., a test might look like this:
-
-```fine
-// @concrete:
-// | File
-// |   ExpressionStatement
-// |     BinaryExpression
-// |       BinaryExpression
-// |         LiteralExpression
-// |           Number:'"1"'
-// |         Star:'"*"'
-// |         LiteralExpression
-// |           Number:'"2"'
-// |       Plus:'"+"'
-// |       BinaryExpression
-// |         UnaryExpression
-// |           Minus:'"-"'
-// |           LiteralExpression
-// |             Number:'"3"'
-// |         Star:'"*"'
-// |         LiteralExpression
-// |           Number:'"4"'
-// |     Semicolon:'";"'
-//
-1 * 2 + -3 * 4;
-
-// @type: 532 f64
-```
-
-## Assertions
-
-The various assertions are as follows:
-
-- The `// @concrete:` assertion says that the following lines
-  (prefixed with `// | `, as above) describe the concrete syntax tree
-  of the file after parsing.
-
-  e.g.:
-
-  ```fine
-  // @concrete:
-  // | File
-  // |   ExpressionStatement
-  // |     LiteralExpression
-  // |       String:'"\"Hello world\""'
-  // |     Semicolon:'";"'
-  //
-  "Hello world";
-  ```
-
-- The `// @type:` assertion says that the type of the tree at the
-  given point will match the given type. `@type` assertions usually go
-  after the contents of the file to make the probe points more stable
-  in the face of new assertions and whatnot.
-
-  e.g.:
-
-  ```fine
-  "Hello world!"
-  // @type: 2 string
-  ```
-
-- The `// @type-error:` assertion says that the type of the tree at
-  the given point should be an error, and that the error message
-  provided should be among the generated errors. (Like `@type`, these
-  usually go after the code, for stability.)
-
-  e.g.:
-
-  ```fine
-  - "twenty five";
-  // @type-error: 0 cannot apply unary operator '-' to value of type string
-  ```

fine/tests/example_tests.rs

@@ -150,7 +150,7 @@ fn assert_type_at(
         None => semantic_panic!(&semantics, "Unable to find the subtee at position {pos}"),
     };
 
-    let tree_type = semantics.type_of(tree_ref);
+    let tree_type = semantics.type_of(tree_ref, true);
     let actual = format!("{}", tree_type.unwrap_or(Type::Error));
     semantic_assert_eq!(
         &semantics,
@@ -173,7 +173,7 @@ fn assert_type_error_at(
         None => semantic_panic!(&semantics, "Unable to find the subtee at position {pos}"),
     };
 
-    let tree_type = semantics.type_of(tree_ref);
+    let tree_type = semantics.type_of(tree_ref, true);
     semantic_assert!(
         &semantics,
         matches!(tree_type, Some(Type::Error)),

fine/tests/expression/arithmetic.fine

@@ -1,4 +1,4 @@
-// @concrete:
+// concrete:
 // | File
 // |   ExpressionStatement
 // |     BinaryExpression
@@ -21,4 +21,4 @@
 //
 1 * 2 + -3 * 4;
 
-// @type: 532 f64
+// type: 532 f64

fine/tests/expression/boolean.fine

@@ -1,4 +1,4 @@
-// @concrete:
+// concrete:
 // | File
 // |   ExpressionStatement
 // |     BinaryExpression
@@ -21,4 +21,4 @@
 //
 true and false or false and !true;
 
-// @type: 549 bool
+// type: 549 bool

fine/tests/expression/conditional.fine

@@ -1,4 +1,4 @@
-// @concrete:
+// concrete:
 // | File
 // |   IfStatement
 // |     ConditionalExpression
@@ -27,18 +27,18 @@ if true { "discarded"; 23 } else { 45 }
 
 // Here come some type probes!
 // (type of the condition)
-// @type: 667 bool
+// type: 667 bool
 //
 // (the discarded expression)
-// @type: 674 string
+// type: 674 string
 //
 // (the "then" clause)
-// @type: 686 f64
-// @type: 689 f64
+// type: 686 f64
+// type: 689 f64
 //
 // (the "else" clause)
-// @type: 696 f64
-// @type: 699 f64
+// type: 696 f64
+// type: 699 f64
 //
 // (the overall expression)
-// @type: 664 f64
+// type: 664 f64

fine/tests/expression/errors/binary_mismatch.fine

@@ -1,4 +1,4 @@
 112 - "twenty five";
 "twenty five" - 112;
-// @type-error: 4 cannot apply binary operator '-' to expressions of type 'f64' (on the left) and 'string' (on the right)
-// @type-error: 35 cannot apply binary operator '-' to expressions of type 'string' (on the left) and 'f64' (on the right)
+// type-error: 4 cannot apply binary operator '-' to expressions of type 'f64' (on the left) and 'string' (on the right)
+// type-error: 35 cannot apply binary operator '-' to expressions of type 'string' (on the left) and 'f64' (on the right)

fine/tests/expression/errors/if_mismatched_arms.fine

@@ -1,2 +1,2 @@
 if true { "blarg" } else { 23 }
-// @type-error: 0 the type of the `then` branch (string) must match the type of the `else` branch (f64)
+// type-error: 0 the type of the `then` branch (string) must match the type of the `else` branch (f64)

fine/tests/expression/errors/if_not_bool.fine

@@ -1,2 +1,2 @@
 if 23 { "what" } else { "the" }
-// @type-error: 0 conditions must yield a boolean
+// type-error: 0 conditions must yield a boolean

fine/tests/expression/errors/if_requires_else.fine

@@ -1,2 +1,2 @@
 if (if false { true }) { 32 } else { 23 }
-// @type-error: 4 the type of the `then` branch (bool) must match the type of the `else` branch (())
+// type-error: 4 this conditional expression needs an else arm to produce a value

fine/tests/expression/errors/unary_mismatch.fine

@@ -1,2 +1,2 @@
 - "twenty five";
-// @type-error: 0 cannot apply unary operator '-' to value of type string
+// type-error: 0 cannot apply unary operator '-' to value of type string

fine/tests/expression/number.fine

@@ -1,4 +1,4 @@
-// @concrete:
+// concrete:
 // | File
 // |   ExpressionStatement
 // |     LiteralExpression
@@ -7,4 +7,4 @@
 
 42;
 
-// @type: 129 f64
+// type: 129 f64

fine/tests/expression/strings.fine

@@ -1,4 +1,4 @@
-// @concrete:
+// concrete:
 // | File
 // |   ExpressionStatement
 // |     BinaryExpression
@@ -11,4 +11,4 @@
 //
 "Hello " + 'world!';
 
-// @type: 261 string
+// type: 261 string