Merge #6645

6645: Publish diagnostics for macro expansion errors r=matklad a=jonas-schievink

This adds 2 new diagnostics, emitted during name resolution:

* `unresolved-proc-macro`, a weak warning that is emitted when a proc macro is supposed to be expanded, but was not provided by the build system. This usually means that proc macro support is turned off, but may also indicate setup issues when using rust-project.json. Being a weak warning, this should help set expectations when users see it, while not being too obstructive. We do not yet emit this for attribute macros though, just custom derives and `!` macros.
* `macro-error`, which is emitted when any macro (procedural or `macro_rules!`) fails to expand due to some error. This is an error-level diagnostic, but currently still marked as experimental, because there might be spurious errors and this hasn't been tested too well.

This does not yet emit diagnostics when expansion in item bodies fails, just for module-level macros.

Known bug: The "proc macro not found" diagnostic points at the whole item for custom derives, it should just point at the macro's name in the `#[derive]` list, but I haven't found an easy way to do that.

Screenshots:

![screenshot-2020-11-26-19:54:14](https://user-images.githubusercontent.com/1786438/100385782-f8bc2300-3023-11eb-9f27-e8f8ce9d6114.png)
![screenshot-2020-11-26-19:55:39](https://user-images.githubusercontent.com/1786438/100385784-f954b980-3023-11eb-9617-ac2eb0a0a9dc.png)


Co-authored-by: Jonas Schievink <[email protected]>

3 files changed, 176 insertions, 5 deletions

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 {