feat: apply #[cfg] to proc macro inputs

crates/cfg/Cargo.toml

@@ -16,6 +16,7 @@ rustc-hash.workspace = true
 
 # locals deps
 tt.workspace = true
+syntax.workspace = true
 
 [dev-dependencies]
 expect-test = "1.4.1"
@@ -28,7 +29,6 @@ derive_arbitrary = "1.3.2"
 
 # local deps
 mbe.workspace = true
-syntax.workspace = true
 
 [lints]
-workspace = true
+workspace = true

crates/cfg/src/cfg_expr.rs

@@ -2,8 +2,12 @@
 //!
 //! See: <https://doc.rust-lang.org/reference/conditional-compilation.html#conditional-compilation>
 
-use std::{fmt, slice::Iter as SliceIter};
+use std::{fmt, iter::Peekable, slice::Iter as SliceIter};
 
+use syntax::{
+    ast::{self, Meta},
+    NodeOrToken,
+};
 use tt::SmolStr;
 
 /// A simple configuration value passed in from the outside.
@@ -47,6 +51,12 @@ impl CfgExpr {
     pub fn parse<S>(tt: &tt::Subtree<S>) -> CfgExpr {
         next_cfg_expr(&mut tt.token_trees.iter()).unwrap_or(CfgExpr::Invalid)
     }
+    /// Parses a `cfg` attribute from the meta
+    pub fn parse_from_attr_meta(meta: Meta) -> Option<CfgExpr> {
+        let tt = meta.token_tree()?;
+        let mut iter = tt.token_trees_and_tokens().skip(1).peekable();
+        next_cfg_expr_from_syntax(&mut iter)
+    }
     /// Fold the cfg by querying all basic `Atom` and `KeyValue` predicates.
     pub fn fold(&self, query: &dyn Fn(&CfgAtom) -> bool) -> Option<bool> {
         match self {
@@ -62,6 +72,69 @@ impl CfgExpr {
         }
     }
 }
+fn next_cfg_expr_from_syntax<I>(iter: &mut Peekable<I>) -> Option<CfgExpr>
+where
+    I: Iterator<Item = NodeOrToken<ast::TokenTree, syntax::SyntaxToken>>,
+{
+    let name = match iter.next() {
+        None => return None,
+        Some(NodeOrToken::Token(element)) => match element.kind() {
+            syntax::T![ident] => SmolStr::new(element.text()),
+            _ => return Some(CfgExpr::Invalid),
+        },
+        Some(_) => return Some(CfgExpr::Invalid),
+    };
+    let result = match name.as_str() {
+        "all" | "any" | "not" => {
+            let mut preds = Vec::new();
+            let Some(NodeOrToken::Node(tree)) = iter.next() else {
+                return Some(CfgExpr::Invalid);
+            };
+            let mut tree_iter = tree.token_trees_and_tokens().skip(1).peekable();
+            while tree_iter
+                .peek()
+                .filter(
+                    |element| matches!(element, NodeOrToken::Token(token) if (token.kind() != syntax::T![')'])),
+                )
+                .is_some()
+            {
+                let pred = next_cfg_expr_from_syntax(&mut tree_iter);
+                if let Some(pred) = pred {
+                    preds.push(pred);
+                }
+            }
+            let group = match name.as_str() {
+                "all" => CfgExpr::All(preds),
+                "any" => CfgExpr::Any(preds),
+                "not" => CfgExpr::Not(Box::new(preds.pop().unwrap_or(CfgExpr::Invalid))),
+                _ => unreachable!(),
+            };
+            Some(group)
+        }
+        _ => match iter.peek() {
+            Some(NodeOrToken::Token(element)) if (element.kind() == syntax::T![=]) => {
+                iter.next();
+                match iter.next() {
+                    Some(NodeOrToken::Token(value_token))
+                        if (value_token.kind() == syntax::SyntaxKind::STRING) =>
+                    {
+                        let value = value_token.text();
+                        let value = SmolStr::new(value.trim_matches('"'));
+                        Some(CfgExpr::Atom(CfgAtom::KeyValue { key: name, value }))
+                    }
+                    _ => None,
+                }
+            }
+            _ => Some(CfgExpr::Atom(CfgAtom::Flag(name))),
+        },
+    };
+    if let Some(NodeOrToken::Token(element)) = iter.peek() {
+        if element.kind() == syntax::T![,] {
+            iter.next();
+        }
+    }
+    result
+}
 
 fn next_cfg_expr<S>(it: &mut SliceIter<'_, tt::TokenTree<S>>) -> Option<CfgExpr> {
     let name = match it.next() {

crates/cfg/src/tests.rs

@@ -1,7 +1,10 @@
 use arbitrary::{Arbitrary, Unstructured};
 use expect_test::{expect, Expect};
 use mbe::{syntax_node_to_token_tree, DummyTestSpanMap, DUMMY};
-use syntax::{ast, AstNode};
+use syntax::{
+    ast::{self, Attr},
+    AstNode, SourceFile,
+};
 
 use crate::{CfgAtom, CfgExpr, CfgOptions, DnfExpr};
 
@@ -12,6 +15,22 @@ fn assert_parse_result(input: &str, expected: CfgExpr) {
     let cfg = CfgExpr::parse(&tt);
     assert_eq!(cfg, expected);
 }
+fn check_dnf_from_syntax(input: &str, expect: Expect) {
+    let parse = SourceFile::parse(input);
+    let node = match parse.tree().syntax().descendants().find_map(Attr::cast) {
+        Some(it) => it,
+        None => {
+            let node = std::any::type_name::<Attr>();
+            panic!("Failed to make ast node `{node}` from text {input}")
+        }
+    };
+    let node = node.clone_subtree();
+    assert_eq!(node.syntax().text_range().start(), 0.into());
+
+    let cfg = CfgExpr::parse_from_attr_meta(node.meta().unwrap()).unwrap();
+    let actual = format!("#![cfg({})]", DnfExpr::new(cfg));
+    expect.assert_eq(&actual);
+}
 
 fn check_dnf(input: &str, expect: Expect) {
     let source_file = ast::SourceFile::parse(input).ok().unwrap();
@@ -86,6 +105,11 @@ fn smoke() {
 
     check_dnf("#![cfg(not(a))]", expect![[r#"#![cfg(not(a))]"#]]);
 }
+#[test]
+fn cfg_from_attr() {
+    check_dnf_from_syntax(r#"#[cfg(test)]"#, expect![[r#"#![cfg(test)]"#]]);
+    check_dnf_from_syntax(r#"#[cfg(not(never))]"#, expect![[r#"#![cfg(not(never))]"#]]);
+}
 
 #[test]
 fn distribute() {

crates/hir-expand/src/cfg_process.rs

@@ -0,0 +1,204 @@
+//! Processes out #[cfg] and #[cfg_attr] attributes from the input for the derive macro
+use rustc_hash::FxHashSet;
+use syntax::{
+    ast::{self, Attr, HasAttrs, Meta, VariantList},
+    AstNode, SyntaxElement, SyntaxNode, T,
+};
+use tracing::{debug, warn};
+
+use crate::{db::ExpandDatabase, MacroCallKind, MacroCallLoc};
+
+fn check_cfg_attr(attr: &Attr, loc: &MacroCallLoc, db: &dyn ExpandDatabase) -> Option<bool> {
+    if !attr.simple_name().as_deref().map(|v| v == "cfg")? {
+        return None;
+    }
+    debug!("Evaluating cfg {}", attr);
+    let cfg = cfg::CfgExpr::parse_from_attr_meta(attr.meta()?)?;
+    debug!("Checking cfg {:?}", cfg);
+    let enabled = db.crate_graph()[loc.krate].cfg_options.check(&cfg) != Some(false);
+    Some(enabled)
+}
+
+fn check_cfg_attr_attr(attr: &Attr, loc: &MacroCallLoc, db: &dyn ExpandDatabase) -> Option<bool> {
+    if !attr.simple_name().as_deref().map(|v| v == "cfg_attr")? {
+        return None;
+    }
+    debug!("Evaluating cfg_attr {}", attr);
+    let cfg_expr = cfg::CfgExpr::parse_from_attr_meta(attr.meta()?)?;
+    debug!("Checking cfg_attr {:?}", cfg_expr);
+    let enabled = db.crate_graph()[loc.krate].cfg_options.check(&cfg_expr) != Some(false);
+    Some(enabled)
+}
+
+fn process_has_attrs_with_possible_comma<I: HasAttrs>(
+    items: impl Iterator<Item = I>,
+    loc: &MacroCallLoc,
+    db: &dyn ExpandDatabase,
+    remove: &mut FxHashSet<SyntaxElement>,
+) -> Option<()> {
+    for item in items {
+        let field_attrs = item.attrs();
+        'attrs: for attr in field_attrs {
+            if check_cfg_attr(&attr, loc, db).map(|enabled| !enabled).unwrap_or_default() {
+                debug!("censoring type {:?}", item.syntax());
+                remove.insert(item.syntax().clone().into());
+                // We need to remove the , as well
+                add_comma(&item, remove);
+                break 'attrs;
+            }
+
+            if let Some(enabled) = check_cfg_attr_attr(&attr, loc, db) {
+                if enabled {
+                    debug!("Removing cfg_attr tokens {:?}", attr);
+                    let meta = attr.meta()?;
+                    let removes_from_cfg_attr = remove_tokens_within_cfg_attr(meta)?;
+                    remove.extend(removes_from_cfg_attr);
+                } else {
+                    debug!("censoring type cfg_attr {:?}", item.syntax());
+                    remove.insert(attr.syntax().clone().into());
+                    continue;
+                }
+            }
+        }
+    }
+    Some(())
+}
+
+fn remove_tokens_within_cfg_attr(meta: Meta) -> Option<FxHashSet<SyntaxElement>> {
+    let mut remove: FxHashSet<SyntaxElement> = FxHashSet::default();
+    debug!("Enabling attribute {}", meta);
+    let meta_path = meta.path()?;
+    debug!("Removing {:?}", meta_path.syntax());
+    remove.insert(meta_path.syntax().clone().into());
+
+    let meta_tt = meta.token_tree()?;
+    debug!("meta_tt {}", meta_tt);
+    // Remove the left paren
+    remove.insert(meta_tt.l_paren_token()?.into());
+    let mut found_comma = false;
+    for tt in meta_tt.token_trees_and_tokens().skip(1) {
+        debug!("Checking {:?}", tt);
+        // Check if it is a subtree or a token. If it is a token check if it is a comma. If so, remove it and break.
+        match tt {
+            syntax::NodeOrToken::Node(node) => {
+                // Remove the entire subtree
+                remove.insert(node.syntax().clone().into());
+            }
+            syntax::NodeOrToken::Token(token) => {
+                if token.kind() == T![,] {
+                    found_comma = true;
+                    remove.insert(token.into());
+                    break;
+                }
+                remove.insert(token.into());
+            }
+        }
+    }
+    if !found_comma {
+        warn!("No comma found in {}", meta_tt);
+        return None;
+    }
+    // Remove the right paren
+    remove.insert(meta_tt.r_paren_token()?.into());
+    Some(remove)
+}
+fn add_comma(item: &impl AstNode, res: &mut FxHashSet<SyntaxElement>) {
+    if let Some(comma) = item.syntax().next_sibling_or_token().filter(|it| it.kind() == T![,]) {
+        res.insert(comma);
+    }
+}
+fn process_enum(
+    variants: VariantList,
+    loc: &MacroCallLoc,
+    db: &dyn ExpandDatabase,
+    remove: &mut FxHashSet<SyntaxElement>,
+) -> Option<()> {
+    'variant: for variant in variants.variants() {
+        for attr in variant.attrs() {
+            if check_cfg_attr(&attr, loc, db).map(|enabled| !enabled).unwrap_or_default() {
+                // Rustc does not strip the attribute if it is enabled. So we will will leave it
+                debug!("censoring type {:?}", variant.syntax());
+                remove.insert(variant.syntax().clone().into());
+                // We need to remove the , as well
+                add_comma(&variant, remove);
+                continue 'variant;
+            };
+
+            if let Some(enabled) = check_cfg_attr_attr(&attr, loc, db) {
+                if enabled {
+                    debug!("Removing cfg_attr tokens {:?}", attr);
+                    let meta = attr.meta()?;
+                    let removes_from_cfg_attr = remove_tokens_within_cfg_attr(meta)?;
+                    remove.extend(removes_from_cfg_attr);
+                } else {
+                    debug!("censoring type cfg_attr {:?}", variant.syntax());
+                    remove.insert(attr.syntax().clone().into());
+                    continue;
+                }
+            }
+        }
+        if let Some(fields) = variant.field_list() {
+            match fields {
+                ast::FieldList::RecordFieldList(fields) => {
+                    process_has_attrs_with_possible_comma(fields.fields(), loc, db, remove)?;
+                }
+                ast::FieldList::TupleFieldList(fields) => {
+                    process_has_attrs_with_possible_comma(fields.fields(), loc, db, remove)?;
+                }
+            }
+        }
+    }
+    Some(())
+}
+
+pub(crate) fn process_cfg_attrs(
+    node: &SyntaxNode,
+    loc: &MacroCallLoc,
+    db: &dyn ExpandDatabase,
+) -> Option<FxHashSet<SyntaxElement>> {
+    // FIXME: #[cfg_eval] is not implemented. But it is not stable yet
+    if !matches!(loc.kind, MacroCallKind::Derive { .. }) {
+        return None;
+    }
+    let mut remove = FxHashSet::default();
+
+    let item = ast::Item::cast(node.clone())?;
+    for attr in item.attrs() {
+        if let Some(enabled) = check_cfg_attr_attr(&attr, loc, db) {
+            if enabled {
+                debug!("Removing cfg_attr tokens {:?}", attr);
+                let meta = attr.meta()?;
+                let removes_from_cfg_attr = remove_tokens_within_cfg_attr(meta)?;
+                remove.extend(removes_from_cfg_attr);
+            } else {
+                debug!("censoring type cfg_attr {:?}", item.syntax());
+                remove.insert(attr.syntax().clone().into());
+                continue;
+            }
+        }
+    }
+    match item {
+        ast::Item::Struct(it) => match it.field_list()? {
+            ast::FieldList::RecordFieldList(fields) => {
+                process_has_attrs_with_possible_comma(fields.fields(), loc, db, &mut remove)?;
+            }
+            ast::FieldList::TupleFieldList(fields) => {
+                process_has_attrs_with_possible_comma(fields.fields(), loc, db, &mut remove)?;
+            }
+        },
+        ast::Item::Enum(it) => {
+            process_enum(it.variant_list()?, loc, db, &mut remove)?;
+        }
+        ast::Item::Union(it) => {
+            process_has_attrs_with_possible_comma(
+                it.record_field_list()?.fields(),
+                loc,
+                db,
+                &mut remove,
+            )?;
+        }
+        // FIXME: Implement for other items if necessary. As we do not support #[cfg_eval] yet, we do not need to implement it for now
+        _ => {}
+    }
+    Some(remove)
+}