Auto merge of #56999 - petrochenkov:macrecov2, r=estebank

AST/HIR: Introduce `ExprKind::Err` for better error recovery in the front-end

This way we can avoid aborting compilation if expansion produces errors and generate `ExprKind::Err`s instead.

3 files changed, 27 insertions, 26 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index d576397c942..1efe0b3478d 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -2,7 +2,7 @@ pub use self::SyntaxExtension::*;
 
 use ast::{self, Attribute, Name, PatKind, MetaItem};
 use attr::HasAttrs;
-use source_map::{self, SourceMap, Spanned, respan};
+use source_map::{SourceMap, Spanned, respan};
 use syntax_pos::{Span, MultiSpan, DUMMY_SP};
 use edition::Edition;
 use errors::{DiagnosticBuilder, DiagnosticId};
@@ -456,7 +456,8 @@ impl MacResult for MacEager {
 #[derive(Copy, Clone)]
 pub struct DummyResult {
     expr_only: bool,
-    span: Span
+    is_error: bool,
+    span: Span,
 }
 
 impl DummyResult {
@@ -464,8 +465,13 @@ impl DummyResult {
     ///
     /// Use this as a return value after hitting any errors and
     /// calling `span_err`.
-    pub fn any(sp: Span) -> Box<dyn MacResult+'static> {
-        Box::new(DummyResult { expr_only: false, span: sp })
+    pub fn any(span: Span) -> Box<dyn MacResult+'static> {
+        Box::new(DummyResult { expr_only: false, is_error: true, span })
+    }
+
+    /// Same as `any`, but must be a valid fragment, not error.
+    pub fn any_valid(span: Span) -> Box<dyn MacResult+'static> {
+        Box::new(DummyResult { expr_only: false, is_error: false, span })
     }
 
     /// Create a default MacResult that can only be an expression.
@@ -473,15 +479,15 @@ impl DummyResult {
     /// Use this for macros that must expand to an expression, so even
     /// if an error is encountered internally, the user will receive
     /// an error that they also used it in the wrong place.
-    pub fn expr(sp: Span) -> Box<dyn MacResult+'static> {
-        Box::new(DummyResult { expr_only: true, span: sp })
+    pub fn expr(span: Span) -> Box<dyn MacResult+'static> {
+        Box::new(DummyResult { expr_only: true, is_error: true, span })
     }
 
     /// A plain dummy expression.
-    pub fn raw_expr(sp: Span) -> P<ast::Expr> {
+    pub fn raw_expr(sp: Span, is_error: bool) -> P<ast::Expr> {
         P(ast::Expr {
             id: ast::DUMMY_NODE_ID,
-            node: ast::ExprKind::Lit(source_map::respan(sp, ast::LitKind::Bool(false))),
+            node: if is_error { ast::ExprKind::Err } else { ast::ExprKind::Tup(Vec::new()) },
             span: sp,
             attrs: ThinVec::new(),
         })
@@ -496,10 +502,11 @@ impl DummyResult {
         }
     }
 
-    pub fn raw_ty(sp: Span) -> P<ast::Ty> {
+    /// A plain dummy type.
+    pub fn raw_ty(sp: Span, is_error: bool) -> P<ast::Ty> {
         P(ast::Ty {
             id: ast::DUMMY_NODE_ID,
-            node: ast::TyKind::Infer,
+            node: if is_error { ast::TyKind::Err } else { ast::TyKind::Tup(Vec::new()) },
             span: sp
         })
     }
@@ -507,7 +514,7 @@ impl DummyResult {
 
 impl MacResult for DummyResult {
     fn make_expr(self: Box<DummyResult>) -> Option<P<ast::Expr>> {
-        Some(DummyResult::raw_expr(self.span))
+        Some(DummyResult::raw_expr(self.span, self.is_error))
     }
 
     fn make_pat(self: Box<DummyResult>) -> Option<P<ast::Pat>> {
@@ -550,13 +557,13 @@ impl MacResult for DummyResult {
     fn make_stmts(self: Box<DummyResult>) -> Option<SmallVec<[ast::Stmt; 1]>> {
         Some(smallvec![ast::Stmt {
             id: ast::DUMMY_NODE_ID,
-            node: ast::StmtKind::Expr(DummyResult::raw_expr(self.span)),
+            node: ast::StmtKind::Expr(DummyResult::raw_expr(self.span, self.is_error)),
             span: self.span,
         }])
     }
 
     fn make_ty(self: Box<DummyResult>) -> Option<P<ast::Ty>> {
-        Some(DummyResult::raw_ty(self.span))
+        Some(DummyResult::raw_ty(self.span, self.is_error))
     }
 }
 
@@ -796,7 +803,6 @@ pub struct ExtCtxt<'a> {
     pub ecfg: expand::ExpansionConfig<'a>,
     pub root_path: PathBuf,
     pub resolver: &'a mut dyn Resolver,
-    pub resolve_err_count: usize,
     pub current_expansion: ExpansionData,
     pub expansions: FxHashMap<Span, Vec<String>>,
 }
@@ -811,7 +817,6 @@ impl<'a> ExtCtxt<'a> {
             ecfg,
             root_path: PathBuf::new(),
             resolver,
-            resolve_err_count: 0,
             current_expansion: ExpansionData {
                 mark: Mark::root(),
                 depth: 0,
diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index 15faae53916..a8eec1a74dd 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -587,7 +587,6 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
            id: ast::DUMMY_NODE_ID,
            rules: BlockCheckMode::Default,
            span,
-           recovered: false,
         })
     }
 
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 55012bb7f5a..3863778fe72 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -344,8 +344,10 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             // FIXME(jseyfried): Refactor out the following logic
             let (expanded_fragment, new_invocations) = if let Some(ext) = ext {
                 if let Some(ext) = ext {
-                    let dummy = invoc.fragment_kind.dummy(invoc.span()).unwrap();
-                    let fragment = self.expand_invoc(invoc, &*ext).unwrap_or(dummy);
+                    let (invoc_fragment_kind, invoc_span) = (invoc.fragment_kind, invoc.span());
+                    let fragment = self.expand_invoc(invoc, &*ext).unwrap_or_else(|| {
+                        invoc_fragment_kind.dummy(invoc_span).unwrap()
+                    });
                     self.collect_invocations(fragment, &[])
                 } else if let InvocationKind::Attr { attr: None, traits, item, .. } = invoc.kind {
                     if !item.derive_allowed() {
@@ -431,9 +433,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
 
     fn resolve_imports(&mut self) {
         if self.monotonic {
-            let err_count = self.cx.parse_sess.span_diagnostic.err_count();
             self.cx.resolver.resolve_imports();
-            self.cx.resolve_err_count += self.cx.parse_sess.span_diagnostic.err_count() - err_count;
         }
     }
 
@@ -457,11 +457,9 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         };
 
         if self.monotonic {
-            let err_count = self.cx.parse_sess.span_diagnostic.err_count();
-            let mark = self.cx.current_expansion.mark;
-            self.cx.resolver.visit_ast_fragment_with_placeholders(mark, &fragment_with_placeholders,
-                                                                  derives);
-            self.cx.resolve_err_count += self.cx.parse_sess.span_diagnostic.err_count() - err_count;
+            self.cx.resolver.visit_ast_fragment_with_placeholders(
+                self.cx.current_expansion.mark, &fragment_with_placeholders, derives
+            );
         }
 
         (fragment_with_placeholders, invocations)
@@ -724,7 +722,6 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                     emit_feature_err(this.cx.parse_sess, &*feature.as_str(), span,
                                      GateIssue::Library(Some(issue)), &explain);
                     this.cx.trace_macros_diag();
-                    return Err(kind.dummy(span));
                 }
             }