refactor(tvix/eval): store spans instead of nodes in Warning/Error r/4737

Another step towards being able to report accurate errors. The codemap
spans contain strictly more accessible information, as they now retain
information about which input file something came from.

This required some shuffling around in the compiler to thread all the
right information to the right places.

Change-Id: I18ccfb20f07b0c33e1c4f51ca00cd09f7b2d19c6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6404
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

2 files changed, 82 insertions, 81 deletions

diff --git a/tvix/eval/src/compiler/mod.rs b/tvix/eval/src/compiler/mod.rs
index aaa8f5c9726f..d2b08a6b105c 100644
--- a/tvix/eval/src/compiler/mod.rs
+++ b/tvix/eval/src/compiler/mod.rs
@@ -103,17 +103,18 @@ impl Compiler<'_> {
         &mut self.context_mut().scope
     }
 
+    fn span_for<N: AstNode>(&self, node: &N) -> codemap::Span {
+        let rowan_span = node.syntax().text_range();
+        self.file.span.subspan(
+            u32::from(rowan_span.start()) as u64,
+            u32::from(rowan_span.end()) as u64,
+        )
+    }
+
     /// Push a single instruction to the current bytecode chunk and
     /// track the source span from which it was compiled.
     fn push_op<T: AstNode>(&mut self, data: OpCode, node: &T) -> CodeIdx {
-        let span: codemap::Span = {
-            let rowan_span = node.syntax().text_range();
-            self.file.span.subspan(
-                u32::from(rowan_span.start()) as u64,
-                u32::from(rowan_span.end()) as u64,
-            )
-        };
-
+        let span = self.span_for(node);
         self.chunk().push_op(data, span)
     }
 
@@ -168,8 +169,9 @@ impl Compiler<'_> {
             ast::LiteralKind::Integer(i) => {
                 self.emit_constant(Value::Integer(i.value().unwrap()), &node);
             }
+
             ast::LiteralKind::Uri(u) => {
-                self.emit_warning(node.syntax().clone(), WarningKind::DeprecatedLiteralURL);
+                self.emit_warning(self.span_for(&node), WarningKind::DeprecatedLiteralURL);
                 self.emit_constant(Value::String(u.syntax().text().into()), &node);
             }
         }
@@ -187,7 +189,7 @@ impl Compiler<'_> {
                 Some(buf) => buf,
                 None => {
                     self.emit_error(
-                        node.syntax().clone(),
+                        self.span_for(&node),
                         ErrorKind::PathResolution("failed to determine home directory".into()),
                     );
                     return;
@@ -645,7 +647,7 @@ impl Compiler<'_> {
                 // scope is a no-op *if* the identifier can be
                 // statically resolved.
                 None if !self.scope().has_with() => {
-                    self.emit_warning(inherit.syntax().clone(), WarningKind::UselessInherit);
+                    self.emit_warning(self.span_for(&inherit), WarningKind::UselessInherit);
                     continue;
                 }
 
@@ -659,15 +661,12 @@ impl Compiler<'_> {
                                 .resolve_local(ident.ident_token().unwrap().text()),
                             LocalPosition::Known(_)
                         ) {
-                            self.emit_warning(ident.syntax().clone(), WarningKind::UselessInherit);
+                            self.emit_warning(self.span_for(&ident), WarningKind::UselessInherit);
                             continue;
                         }
 
                         self.compile_ident(slot, ident.clone());
-                        let idx = self.declare_local(
-                            ident.syntax().clone(),
-                            ident.ident_token().unwrap().text(),
-                        );
+                        let idx = self.declare_local(&ident, ident.ident_token().unwrap().text());
                         self.scope_mut().mark_initialised(idx);
                     }
                 }
@@ -679,10 +678,7 @@ impl Compiler<'_> {
 
                         self.emit_literal_ident(&ident);
                         self.push_op(OpCode::OpAttrsSelect, &ident);
-                        let idx = self.declare_local(
-                            ident.syntax().clone(),
-                            ident.ident_token().unwrap().text(),
-                        );
+                        let idx = self.declare_local(&ident, ident.ident_token().unwrap().text());
                         self.scope_mut().mark_initialised(idx);
                     }
                 }
@@ -704,7 +700,7 @@ impl Compiler<'_> {
         // required for resolving recursion.
         let mut entries: Vec<(LocalIdx, ast::Expr)> = vec![];
         for entry in node.attrpath_values() {
-            let mut path = match normalise_ident_path(entry.attrpath().unwrap().attrs()) {
+            let mut path = match self.normalise_ident_path(entry.attrpath().unwrap().attrs()) {
                 Ok(p) => p,
                 Err(err) => {
                     self.errors.push(err);
@@ -716,10 +712,7 @@ impl Compiler<'_> {
                 todo!("nested bindings in let expressions :(")
             }
 
-            let idx = self.declare_local(
-                entry.attrpath().unwrap().syntax().clone(),
-                path.pop().unwrap(),
-            );
+            let idx = self.declare_local(&entry.attrpath().unwrap(), path.pop().unwrap());
 
             entries.push((idx, entry.value().unwrap()));
         }
@@ -787,7 +780,7 @@ impl Compiler<'_> {
                 }
 
                 if !self.scope().has_with() {
-                    self.emit_error(node.syntax().clone(), ErrorKind::UnknownStaticVariable);
+                    self.emit_error(self.span_for(&node), ErrorKind::UnknownStaticVariable);
                     return;
                 }
 
@@ -827,7 +820,8 @@ impl Compiler<'_> {
         self.compile(slot, node.namespace().unwrap());
         self.emit_force(&node.namespace().unwrap());
 
-        let local_idx = self.scope_mut().declare_phantom();
+        let span = self.span_for(&node.namespace().unwrap());
+        let local_idx = self.scope_mut().declare_phantom(span);
         let with_idx = self.scope().stack_index(local_idx);
 
         self.scope_mut().push_with();
@@ -859,7 +853,7 @@ impl Compiler<'_> {
                     .text()
                     .to_string();
 
-                let idx = self.declare_local(param.syntax().clone(), &name);
+                let idx = self.declare_local(&param, &name);
                 self.scope_mut().mark_initialised(idx);
             }
         }
@@ -1047,14 +1041,11 @@ impl Compiler<'_> {
             // accessed while it existed and emit a warning to the
             // user otherwise.
             if let Some(Local {
-                node: Some(node),
-                used,
-                name,
-                ..
+                span, used, name, ..
             }) = self.scope_mut().locals.pop()
             {
                 if !used && !name.starts_with('_') {
-                    self.emit_warning(node, WarningKind::UnusedBinding);
+                    self.emit_warning(span, WarningKind::UnusedBinding);
                 }
             }
         }
@@ -1067,7 +1058,7 @@ impl Compiler<'_> {
     /// Declare a local variable known in the scope that is being
     /// compiled by pushing it to the locals. This is used to
     /// determine the stack offset of variables.
-    fn declare_local<S: Into<String>>(&mut self, node: rnix::SyntaxNode, name: S) -> LocalIdx {
+    fn declare_local<S: Into<String>, N: AstNode>(&mut self, node: &N, name: S) -> LocalIdx {
         let name = name.into();
         let depth = self.scope().scope_depth;
 
@@ -1079,7 +1070,10 @@ impl Compiler<'_> {
         };
 
         if let Some(global_ident) = key {
-            self.emit_warning(node.clone(), WarningKind::ShadowedGlobal(global_ident));
+            self.emit_warning(
+                self.span_for(node),
+                WarningKind::ShadowedGlobal(global_ident),
+            );
             self.scope_mut().poison(global_ident, depth);
         }
 
@@ -1093,12 +1087,13 @@ impl Compiler<'_> {
 
         if shadowed {
             self.emit_error(
-                node.clone(),
+                self.span_for(node),
                 ErrorKind::VariableAlreadyDefined(name.clone()),
             );
         }
 
-        self.scope_mut().declare_local(name, node)
+        let span = self.span_for(node);
+        self.scope_mut().declare_local(name, span)
     }
 
     fn resolve_upvalue(
@@ -1217,56 +1212,62 @@ impl Compiler<'_> {
         self.push_op(OpCode::OpForce, node);
     }
 
-    fn emit_warning(&mut self, node: rnix::SyntaxNode, kind: WarningKind) {
-        self.warnings.push(EvalWarning { node, kind })
+    fn emit_warning(&mut self, span: codemap::Span, kind: WarningKind) {
+        self.warnings.push(EvalWarning { kind, span })
     }
 
-    fn emit_error(&mut self, node: rnix::SyntaxNode, kind: ErrorKind) {
+    fn emit_error(&mut self, span: codemap::Span, kind: ErrorKind) {
         self.errors.push(Error {
-            node: Some(node),
             kind,
+            span: Some(span),
         })
     }
-}
 
-/// Convert a non-dynamic string expression to a string if possible,
-/// or raise an error.
-fn expr_str_to_string(expr: ast::Str) -> EvalResult<String> {
-    if expr.normalized_parts().len() == 1 {
-        if let ast::InterpolPart::Literal(s) = expr.normalized_parts().pop().unwrap() {
-            return Ok(s);
+    /// Convert a non-dynamic string expression to a string if possible,
+    /// or raise an error.
+    fn expr_str_to_string(&self, expr: ast::Str) -> EvalResult<String> {
+        if expr.normalized_parts().len() == 1 {
+            if let ast::InterpolPart::Literal(s) = expr.normalized_parts().pop().unwrap() {
+                return Ok(s);
+            }
         }
-    }
 
-    return Err(Error {
-        node: Some(expr.syntax().clone()),
-        kind: ErrorKind::DynamicKeyInLet(expr.syntax().clone()),
-    });
-}
+        return Err(Error {
+            kind: ErrorKind::DynamicKeyInLet(expr.syntax().clone()),
+            span: Some(self.span_for(&expr)),
+        });
+    }
 
-/// Convert a single identifier path fragment to a string if possible,
-/// or raise an error about the node being dynamic.
-fn attr_to_string(node: ast::Attr) -> EvalResult<String> {
-    match node {
-        ast::Attr::Ident(ident) => Ok(ident.ident_token().unwrap().text().into()),
-        ast::Attr::Str(s) => expr_str_to_string(s),
-
-        // The dynamic node type is just a wrapper. C++ Nix does not
-        // care about the dynamic wrapper when determining whether the
-        // node itself is dynamic, it depends solely on the expression
-        // inside (i.e. `let ${"a"} = 1; in a` is valid).
-        ast::Attr::Dynamic(ref dynamic) => match dynamic.expr().unwrap() {
-            ast::Expr::Str(s) => expr_str_to_string(s),
-            _ => Err(ErrorKind::DynamicKeyInLet(node.syntax().clone()).into()),
-        },
+    /// Convert a single identifier path fragment to a string if possible,
+    /// or raise an error about the node being dynamic.
+    fn attr_to_string(&self, node: ast::Attr) -> EvalResult<String> {
+        match node {
+            ast::Attr::Ident(ident) => Ok(ident.ident_token().unwrap().text().into()),
+            ast::Attr::Str(s) => self.expr_str_to_string(s),
+
+            // The dynamic node type is just a wrapper. C++ Nix does not
+            // care about the dynamic wrapper when determining whether the
+            // node itself is dynamic, it depends solely on the expression
+            // inside (i.e. `let ${"a"} = 1; in a` is valid).
+            ast::Attr::Dynamic(ref dynamic) => match dynamic.expr().unwrap() {
+                ast::Expr::Str(s) => self.expr_str_to_string(s),
+                _ => Err(Error {
+                    kind: ErrorKind::DynamicKeyInLet(node.syntax().clone()),
+                    span: Some(self.span_for(&node)),
+                }),
+            },
+        }
     }
-}
 
-// Normalises identifier fragments into a single string vector for
-// `let`-expressions; fails if fragments requiring dynamic computation
-// are encountered.
-fn normalise_ident_path<I: Iterator<Item = ast::Attr>>(path: I) -> EvalResult<Vec<String>> {
-    path.map(attr_to_string).collect()
+    // Normalises identifier fragments into a single string vector for
+    // `let`-expressions; fails if fragments requiring dynamic computation
+    // are encountered.
+    fn normalise_ident_path<I: Iterator<Item = ast::Attr>>(
+        &self,
+        path: I,
+    ) -> EvalResult<Vec<String>> {
+        path.map(|node| self.attr_to_string(node)).collect()
+    }
 }
 
 /// Prepare the full set of globals from additional globals supplied
diff --git a/tvix/eval/src/compiler/scope.rs b/tvix/eval/src/compiler/scope.rs
index 7614fc2b2b11..b1ad4bfcd2b7 100644
--- a/tvix/eval/src/compiler/scope.rs
+++ b/tvix/eval/src/compiler/scope.rs
@@ -27,8 +27,8 @@ pub struct Local {
     // of `let`-expressions.
     pub name: String,
 
-    // Syntax node at which this local was declared.
-    pub node: Option<rnix::SyntaxNode>,
+    // Source span at which this local was declared.
+    pub span: codemap::Span,
 
     // Scope depth of this local.
     pub depth: usize,
@@ -203,14 +203,14 @@ impl Scope {
     /// Declare a local variable that occupies a stack slot and should
     /// be accounted for, but is not directly accessible by users
     /// (e.g. attribute sets used for `with`).
-    pub fn declare_phantom(&mut self) -> LocalIdx {
+    pub fn declare_phantom(&mut self, span: codemap::Span) -> LocalIdx {
         let idx = self.locals.len();
         self.locals.push(Local {
+            span,
             depth: self.scope_depth,
             initialised: true,
             needs_finaliser: false,
             name: "".into(),
-            node: None,
             phantom: true,
             used: true,
         });
@@ -219,14 +219,14 @@ impl Scope {
     }
 
     /// Declare an uninitialised local variable.
-    pub fn declare_local(&mut self, name: String, node: rnix::SyntaxNode) -> LocalIdx {
+    pub fn declare_local(&mut self, name: String, span: codemap::Span) -> LocalIdx {
         let idx = self.locals.len();
         self.locals.push(Local {
             name,
+            span,
             depth: self.scope_depth,
             initialised: false,
             needs_finaliser: false,
-            node: Some(node),
             phantom: false,
             used: false,
         });