9 files changed, 286 insertions, 34 deletions

diff --git a/crates/hir_def/src/body.rs b/crates/hir_def/src/body.rs
index d10b1af01..33eb5e78c 100644
--- a/crates/hir_def/src/body.rs
+++ b/crates/hir_def/src/body.rs
@@ -14,8 +14,8 @@ use cfg::CfgOptions;
 use drop_bomb::DropBomb;
 use either::Either;
 use hir_expand::{
-    ast_id_map::AstIdMap, diagnostics::DiagnosticSink, hygiene::Hygiene, AstId, HirFileId, InFile,
-    MacroDefId,
+    ast_id_map::AstIdMap, diagnostics::DiagnosticSink, hygiene::Hygiene, AstId, ExpandResult,
+    HirFileId, InFile, MacroDefId,
 };
 use rustc_hash::FxHashMap;
 use syntax::{ast, AstNode, AstPtr};
@@ -102,11 +102,11 @@ impl Expander {
         db: &dyn DefDatabase,
         local_scope: Option<&ItemScope>,
         macro_call: ast::MacroCall,
-    ) -> Option<(Mark, T)> {
+    ) -> ExpandResult<Option<(Mark, T)>> {
         self.recursion_limit += 1;
         if self.recursion_limit > EXPANSION_RECURSION_LIMIT {
             mark::hit!(your_stack_belongs_to_me);
-            return None;
+            return ExpandResult::str_err("reached recursion limit during macro expansion".into());
         }
 
         let macro_call = InFile::new(self.current_file_id, &macro_call);
@@ -120,28 +120,55 @@ impl Expander {
             self.resolve_path_as_macro(db, &path)
         };
 
-        if let Some(call_id) = macro_call.as_call_id(db, self.crate_def_map.krate, resolver) {
-            let file_id = call_id.as_file();
-            if let Some(node) = db.parse_or_expand(file_id) {
-                if let Some(expr) = T::cast(node) {
-                    log::debug!("macro expansion {:#?}", expr.syntax());
-
-                    let mark = Mark {
-                        file_id: self.current_file_id,
-                        ast_id_map: mem::take(&mut self.ast_id_map),
-                        bomb: DropBomb::new("expansion mark dropped"),
-                    };
-                    self.cfg_expander.hygiene = Hygiene::new(db.upcast(), file_id);
-                    self.current_file_id = file_id;
-                    self.ast_id_map = db.ast_id_map(file_id);
-                    return Some((mark, expr));
+        let call_id = match macro_call.as_call_id(db, self.crate_def_map.krate, resolver) {
+            Some(it) => it,
+            None => {
+                // FIXME: this can mean other things too, but `as_call_id` doesn't provide enough
+                // info.
+                return ExpandResult::only_err(mbe::ExpandError::Other(
+                    "failed to parse or resolve macro invocation".into(),
+                ));
+            }
+        };
+
+        let err = db.macro_expand_error(call_id);
+
+        let file_id = call_id.as_file();
+
+        let raw_node = match db.parse_or_expand(file_id) {
+            Some(it) => it,
+            None => {
+                // Only `None` if the macro expansion produced no usable AST.
+                if err.is_none() {
+                    log::warn!("no error despite `parse_or_expand` failing");
                 }
+
+                return ExpandResult::only_err(err.unwrap_or_else(|| {
+                    mbe::ExpandError::Other("failed to parse macro invocation".into())
+                }));
             }
-        }
+        };
+
+        let node = match T::cast(raw_node) {
+            Some(it) => it,
+            None => {
+                // This can happen without being an error, so only forward previous errors.
+                return ExpandResult { value: None, err };
+            }
+        };
+
+        log::debug!("macro expansion {:#?}", node.syntax());
+
+        let mark = Mark {
+            file_id: self.current_file_id,
+            ast_id_map: mem::take(&mut self.ast_id_map),
+            bomb: DropBomb::new("expansion mark dropped"),
+        };
+        self.cfg_expander.hygiene = Hygiene::new(db.upcast(), file_id);
+        self.current_file_id = file_id;
+        self.ast_id_map = db.ast_id_map(file_id);
 
-        // FIXME: Instead of just dropping the error from expansion
-        // report it
-        None
+        ExpandResult { value: Some((mark, node)), err }
     }
 
     pub(crate) fn exit(&mut self, db: &dyn DefDatabase, mut mark: Mark) {
diff --git a/crates/hir_def/src/body/diagnostics.rs b/crates/hir_def/src/body/diagnostics.rs
index e57bdc133..1de7d30e2 100644
--- a/crates/hir_def/src/body/diagnostics.rs
+++ b/crates/hir_def/src/body/diagnostics.rs
@@ -2,11 +2,13 @@
 
 use hir_expand::diagnostics::DiagnosticSink;
 
-use crate::diagnostics::InactiveCode;
+use crate::diagnostics::{InactiveCode, MacroError, UnresolvedProcMacro};
 
 #[derive(Debug, Eq, PartialEq)]
 pub(crate) enum BodyDiagnostic {
     InactiveCode(InactiveCode),
+    MacroError(MacroError),
+    UnresolvedProcMacro(UnresolvedProcMacro),
 }
 
 impl BodyDiagnostic {
@@ -15,6 +17,12 @@ impl BodyDiagnostic {
             BodyDiagnostic::InactiveCode(diag) => {
                 sink.push(diag.clone());
             }
+            BodyDiagnostic::MacroError(diag) => {
+                sink.push(diag.clone());
+            }
+            BodyDiagnostic::UnresolvedProcMacro(diag) => {
+                sink.push(diag.clone());
+            }
         }
     }
 }
diff --git a/crates/hir_def/src/body/lower.rs b/crates/hir_def/src/body/lower.rs
index cd7958746..2c41c0005 100644
--- a/crates/hir_def/src/body/lower.rs
+++ b/crates/hir_def/src/body/lower.rs
@@ -8,7 +8,7 @@ use either::Either;
 use hir_expand::{
     hygiene::Hygiene,
     name::{name, AsName, Name},
-    HirFileId, MacroDefId, MacroDefKind,
+    ExpandError, HirFileId, MacroDefId, MacroDefKind,
 };
 use rustc_hash::FxHashMap;
 use syntax::{
@@ -25,7 +25,7 @@ use crate::{
     body::{Body, BodySourceMap, Expander, PatPtr, SyntheticSyntax},
     builtin_type::{BuiltinFloat, BuiltinInt},
     db::DefDatabase,
-    diagnostics::InactiveCode,
+    diagnostics::{InactiveCode, MacroError, UnresolvedProcMacro},
     expr::{
         dummy_expr_id, ArithOp, Array, BinaryOp, BindingAnnotation, CmpOp, Expr, ExprId, Literal,
         LogicOp, MatchArm, Ordering, Pat, PatId, RecordFieldPat, RecordLitField, Statement,
@@ -561,7 +561,32 @@ impl ExprCollector<'_> {
                     self.alloc_expr(Expr::Missing, syntax_ptr)
                 } else {
                     let macro_call = self.expander.to_source(AstPtr::new(&e));
-                    match self.expander.enter_expand(self.db, Some(&self.body.item_scope), e) {
+                    let res = self.expander.enter_expand(self.db, Some(&self.body.item_scope), e);
+
+                    match res.err {
+                        Some(ExpandError::UnresolvedProcMacro) => {
+                            self.source_map.diagnostics.push(BodyDiagnostic::UnresolvedProcMacro(
+                                UnresolvedProcMacro {
+                                    file: self.expander.current_file_id,
+                                    node: syntax_ptr.clone().into(),
+                                    precise_location: None,
+                                    macro_name: None,
+                                },
+                            ));
+                        }
+                        Some(err) => {
+                            self.source_map.diagnostics.push(BodyDiagnostic::MacroError(
+                                MacroError {
+                                    file: self.expander.current_file_id,
+                                    node: syntax_ptr.clone().into(),
+                                    message: err.to_string(),
+                                },
+                            ));
+                        }
+                        None => {}
+                    }
+
+                    match res.value {
                         Some((mark, expansion)) => {
                             self.source_map
                                 .expansions
diff --git a/crates/hir_def/src/data.rs b/crates/hir_def/src/data.rs
index ff1ef0df6..146045938 100644
--- a/crates/hir_def/src/data.rs
+++ b/crates/hir_def/src/data.rs
@@ -257,7 +257,7 @@ fn collect_items(
                 let root = db.parse_or_expand(file_id).unwrap();
                 let call = ast_id_map.get(call.ast_id).to_node(&root);
 
-                if let Some((mark, mac)) = expander.enter_expand(db, None, call) {
+                if let Some((mark, mac)) = expander.enter_expand(db, None, call).value {
                     let src: InFile<ast::MacroItems> = expander.to_source(mac);
                     let item_tree = db.item_tree(src.file_id);
                     let iter =
diff --git a/crates/hir_def/src/diagnostics.rs b/crates/hir_def/src/diagnostics.rs
index b221b290c..c71266dc0 100644
--- a/crates/hir_def/src/diagnostics.rs
+++ b/crates/hir_def/src/diagnostics.rs
@@ -6,7 +6,7 @@ use stdx::format_to;
 use cfg::{CfgExpr, CfgOptions, DnfExpr};
 use hir_expand::diagnostics::{Diagnostic, DiagnosticCode, DiagnosticSink};
 use hir_expand::{HirFileId, InFile};
-use syntax::{ast, AstPtr, SyntaxNodePtr};
+use syntax::{ast, AstPtr, SyntaxNodePtr, TextRange};
 
 use crate::{db::DefDatabase, DefWithBodyId};
 
@@ -127,3 +127,68 @@ impl Diagnostic for InactiveCode {
         self
     }
 }
+
+// Diagnostic: unresolved-proc-macro
+//
+// This diagnostic is shown when a procedural macro can not be found. This usually means that
+// procedural macro support is simply disabled (and hence is only a weak hint instead of an error),
+// but can also indicate project setup problems.
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub struct UnresolvedProcMacro {
+    pub file: HirFileId,
+    pub node: SyntaxNodePtr,
+    /// If the diagnostic can be pinpointed more accurately than via `node`, this is the `TextRange`
+    /// to use instead.
+    pub precise_location: Option<TextRange>,
+    pub macro_name: Option<String>,
+}
+
+impl Diagnostic for UnresolvedProcMacro {
+    fn code(&self) -> DiagnosticCode {
+        DiagnosticCode("unresolved-proc-macro")
+    }
+
+    fn message(&self) -> String {
+        match &self.macro_name {
+            Some(name) => format!("proc macro `{}` not expanded", name),
+            None => "proc macro not expanded".to_string(),
+        }
+    }
+
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile::new(self.file, self.node.clone())
+    }
+
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+}
+
+// Diagnostic: macro-error
+//
+// This diagnostic is shown for macro expansion errors.
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub struct MacroError {
+    pub file: HirFileId,
+    pub node: SyntaxNodePtr,
+    pub message: String,
+}
+
+impl Diagnostic for MacroError {
+    fn code(&self) -> DiagnosticCode {
+        DiagnosticCode("macro-error")
+    }
+    fn message(&self) -> String {
+        self.message.clone()
+    }
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile::new(self.file, self.node.clone())
+    }
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+    fn is_experimental(&self) -> bool {
+        // Newly added and not very well-tested, might contain false positives.
+        true
+    }
+}
diff --git a/crates/hir_def/src/nameres.rs b/crates/hir_def/src/nameres.rs
index 202a7dcb6..ffd0381d4 100644
--- a/crates/hir_def/src/nameres.rs
+++ b/crates/hir_def/src/nameres.rs
@@ -286,8 +286,9 @@ mod diagnostics {
     use cfg::{CfgExpr, CfgOptions};
     use hir_expand::diagnostics::DiagnosticSink;
     use hir_expand::hygiene::Hygiene;
-    use hir_expand::InFile;
-    use syntax::{ast, AstPtr};
+    use hir_expand::{InFile, MacroCallKind};
+    use syntax::ast::AttrsOwner;
+    use syntax::{ast, AstNode, AstPtr, SyntaxKind, SyntaxNodePtr};
 
     use crate::path::ModPath;
     use crate::{db::DefDatabase, diagnostics::*, nameres::LocalModuleId, AstId};
@@ -301,6 +302,10 @@ mod diagnostics {
         UnresolvedImport { ast: AstId<ast::Use>, index: usize },
 
         UnconfiguredCode { ast: AstId<ast::Item>, cfg: CfgExpr, opts: CfgOptions },
+
+        UnresolvedProcMacro { ast: MacroCallKind },
+
+        MacroError { ast: MacroCallKind, message: String },
     }
 
     #[derive(Debug, PartialEq, Eq)]
@@ -348,6 +353,18 @@ mod diagnostics {
             Self { in_module: container, kind: DiagnosticKind::UnconfiguredCode { ast, cfg, opts } }
         }
 
+        pub(super) fn unresolved_proc_macro(container: LocalModuleId, ast: MacroCallKind) -> Self {
+            Self { in_module: container, kind: DiagnosticKind::UnresolvedProcMacro { ast } }
+        }
+
+        pub(super) fn macro_error(
+            container: LocalModuleId,
+            ast: MacroCallKind,
+            message: String,
+        ) -> Self {
+            Self { in_module: container, kind: DiagnosticKind::MacroError { ast, message } }
+        }
+
         pub(super) fn add_to(
             &self,
             db: &dyn DefDatabase,
@@ -407,6 +424,72 @@ mod diagnostics {
                         opts: opts.clone(),
                     });
                 }
+
+                DiagnosticKind::UnresolvedProcMacro { ast } => {
+                    let mut precise_location = None;
+                    let (file, ast, name) = match ast {
+                        MacroCallKind::FnLike(ast) => {
+                            let node = ast.to_node(db.upcast());
+                            (ast.file_id, SyntaxNodePtr::from(AstPtr::new(&node)), None)
+                        }
+                        MacroCallKind::Attr(ast, name) => {
+                            let node = ast.to_node(db.upcast());
+
+                            // Compute the precise location of the macro name's token in the derive
+                            // list.
+                            // FIXME: This does not handle paths to the macro, but neither does the
+                            // rest of r-a.
+                            let derive_attrs =
+                                node.attrs().filter_map(|attr| match attr.as_simple_call() {
+                                    Some((name, args)) if name == "derive" => Some(args),
+                                    _ => None,
+                                });
+                            'outer: for attr in derive_attrs {
+                                let tokens =
+                                    attr.syntax().children_with_tokens().filter_map(|elem| {
+                                        match elem {
+                                            syntax::NodeOrToken::Node(_) => None,
+                                            syntax::NodeOrToken::Token(tok) => Some(tok),
+                                        }
+                                    });
+                                for token in tokens {
+                                    if token.kind() == SyntaxKind::IDENT
+                                        && token.to_string() == *name
+                                    {
+                                        precise_location = Some(token.text_range());
+                                        break 'outer;
+                                    }
+                                }
+                            }
+
+                            (
+                                ast.file_id,
+                                SyntaxNodePtr::from(AstPtr::new(&node)),
+                                Some(name.clone()),
+                            )
+                        }
+                    };
+                    sink.push(UnresolvedProcMacro {
+                        file,
+                        node: ast,
+                        precise_location,
+                        macro_name: name,
+                    });
+                }
+
+                DiagnosticKind::MacroError { ast, message } => {
+                    let (file, ast) = match ast {
+                        MacroCallKind::FnLike(ast) => {
+                            let node = ast.to_node(db.upcast());
+                            (ast.file_id, SyntaxNodePtr::from(AstPtr::new(&node)))
+                        }
+                        MacroCallKind::Attr(ast, _) => {
+                            let node = ast.to_node(db.upcast());
+                            (ast.file_id, SyntaxNodePtr::from(AstPtr::new(&node)))
+                        }
+                    };
+                    sink.push(MacroError { file, node: ast, message: message.clone() });
+                }
             }
         }
     }
diff --git a/crates/hir_def/src/nameres/collector.rs b/crates/hir_def/src/nameres/collector.rs
index 5ed9073e0..19cd713ba 100644
--- a/crates/hir_def/src/nameres/collector.rs
+++ b/crates/hir_def/src/nameres/collector.rs
@@ -7,7 +7,6 @@ use std::iter;
 
 use base_db::{CrateId, FileId, ProcMacroId};
 use cfg::{CfgExpr, CfgOptions};
-use hir_expand::InFile;
 use hir_expand::{
     ast_id_map::FileAstId,
     builtin_derive::find_builtin_derive,
@@ -16,6 +15,7 @@ use hir_expand::{
     proc_macro::ProcMacroExpander,
     HirFileId, MacroCallId, MacroDefId, MacroDefKind,
 };
+use hir_expand::{InFile, MacroCallLoc};
 use rustc_hash::{FxHashMap, FxHashSet};
 use syntax::ast;
 use test_utils::mark;
@@ -812,7 +812,30 @@ impl DefCollector<'_> {
             log::warn!("macro expansion is too deep");
             return;
         }
-        let file_id: HirFileId = macro_call_id.as_file();
+        let file_id = macro_call_id.as_file();
+
+        // First, fetch the raw expansion result for purposes of error reporting. This goes through
+        // `macro_expand_error` to avoid depending on the full expansion result (to improve
+        // incrementality).
+        let err = self.db.macro_expand_error(macro_call_id);
+        if let Some(err) = err {
+            if let MacroCallId::LazyMacro(id) = macro_call_id {
+                let loc: MacroCallLoc = self.db.lookup_intern_macro(id);
+
+                let diag = match err {
+                    hir_expand::ExpandError::UnresolvedProcMacro => {
+                        // Missing proc macros are non-fatal, so they are handled specially.
+                        DefDiagnostic::unresolved_proc_macro(module_id, loc.kind)
+                    }
+                    _ => DefDiagnostic::macro_error(module_id, loc.kind, err.to_string()),
+                };
+
+                self.def_map.diagnostics.push(diag);
+            }
+            // FIXME: Handle eager macros.
+        }
+
+        // Then, fetch and process the item tree. This will reuse the expansion result from above.
         let item_tree = self.db.item_tree(file_id);
         let mod_dir = self.mod_dirs[&module_id].clone();
         ModCollector {
diff --git a/crates/hir_def/src/nameres/tests/mod_resolution.rs b/crates/hir_def/src/nameres/tests/mod_resolution.rs
index ba295fd9e..ef6f85e15 100644
--- a/crates/hir_def/src/nameres/tests/mod_resolution.rs
+++ b/crates/hir_def/src/nameres/tests/mod_resolution.rs
@@ -798,3 +798,24 @@ mod foo;
 "#,
     );
 }
+
+#[test]
+fn abs_path_ignores_local() {
+    check(
+        r#"
+//- /main.rs crate:main deps:core
+pub use ::core::hash::Hash;
+pub mod core {}
+
+//- /lib.rs crate:core
+pub mod hash { pub trait Hash {} }
+"#,
+        expect![[r#"
+            crate
+            Hash: t
+            core: t
+
+            crate::core
+        "#]],
+    );
+}
diff --git a/crates/hir_def/src/path/lower/lower_use.rs b/crates/hir_def/src/path/lower/lower_use.rs
index 53cecb05f..ba0d1f0e7 100644
--- a/crates/hir_def/src/path/lower/lower_use.rs
+++ b/crates/hir_def/src/path/lower/lower_use.rs
@@ -76,7 +76,7 @@ fn convert_path(prefix: Option<ModPath>, path: ast::Path, hygiene: &Hygiene) ->
                 Either::Left(name) => {
                     // no type args in use
                     let mut res = prefix.unwrap_or_else(|| ModPath {
-                        kind: PathKind::Plain,
+                        kind: segment.coloncolon_token().map_or(PathKind::Plain, |_| PathKind::Abs),
                         segments: Vec::with_capacity(1),
                     });
                     res.segments.push(name);