Warn if include macro fails to include entire file

src/librustc/lint/builtin.rs

@@ -368,6 +368,12 @@ pub mod parser {
         Allow,
         "possible meta-variable misuse at macro definition"
     }
+
+    declare_lint! {
+        pub INCOMPLETE_INCLUDE,
+        Deny,
+        "trailing content in included file"
+    }
 }
 
 declare_lint! {

src/librustc/lint/mod.rs

@@ -28,6 +28,7 @@ use crate::hir::intravisit;
 use crate::hir;
 use crate::lint::builtin::BuiltinLintDiagnostics;
 use crate::lint::builtin::parser::{ILL_FORMED_ATTRIBUTE_INPUT, META_VARIABLE_MISUSE};
+use crate::lint::builtin::parser::INCOMPLETE_INCLUDE;
 use crate::session::{Session, DiagnosticMessageId};
 use crate::ty::TyCtxt;
 use crate::ty::query::Providers;
@@ -83,6 +84,7 @@ impl Lint {
         match lint_id {
             BufferedEarlyLintId::IllFormedAttributeInput => ILL_FORMED_ATTRIBUTE_INPUT,
             BufferedEarlyLintId::MetaVariableMisuse => META_VARIABLE_MISUSE,
+            BufferedEarlyLintId::IncompleteInclude => INCOMPLETE_INCLUDE,
         }
     }
 

src/libsyntax/early_buffered_lints.rs

@@ -11,6 +11,7 @@ use syntax_pos::MultiSpan;
 pub enum BufferedEarlyLintId {
     IllFormedAttributeInput,
     MetaVariableMisuse,
+    IncompleteInclude,
 }
 
 /// Stores buffered lint info which can later be passed to `librustc`.

src/libsyntax_ext/source_util.rs

@@ -5,6 +5,7 @@ use syntax::print::pprust;
 use syntax::ptr::P;
 use syntax::symbol::Symbol;
 use syntax::tokenstream::TokenStream;
+use syntax::early_buffered_lints::BufferedEarlyLintId;
 
 use smallvec::SmallVec;
 use syntax_pos::{self, Pos, Span};
@@ -83,7 +84,16 @@ pub fn expand_include<'cx>(cx: &'cx mut ExtCtxt<'_>, sp: Span, tts: TokenStream)
     }
     impl<'a> base::MacResult for ExpandResult<'a> {
         fn make_expr(mut self: Box<ExpandResult<'a>>) -> Option<P<ast::Expr>> {
-            Some(panictry!(self.p.parse_expr()))
+            let r = panictry!(self.p.parse_expr());
+            if self.p.token != token::Eof {
+                self.p.sess.buffer_lint(
+                    BufferedEarlyLintId::IncompleteInclude,
+                    self.p.token.span,
+                    ast::CRATE_NODE_ID,
+                    "include macro expected single expression in source",
+                );
+            }
+            Some(r)
         }
 
         fn make_items(mut self: Box<ExpandResult<'a>>) -> Option<SmallVec<[P<ast::Item>; 1]>> {

src/test/ui/include-single-expr-helper-1.rs

@@ -0,0 +1,5 @@
+// ignore-test auxiliary file for include-single-expr.rs
+
+0
+
+// trailing comment permitted

src/test/ui/include-single-expr-helper.rs

@@ -0,0 +1,5 @@
+// ignore-test auxiliary file for include-single-expr.rs
+
+0
+10
+100

src/test/ui/include-single-expr.rs

@@ -0,0 +1,6 @@
+// error-pattern include macro expected single expression
+
+fn main() {
+    include!("include-single-expr-helper.rs");
+    include!("include-single-expr-helper-1.rs");
+}

src/test/ui/include-single-expr.stderr

@@ -0,0 +1,10 @@
+error: include macro expected single expression in source
+  --> $DIR/include-single-expr-helper.rs:4:1
+   |
+LL | 10
+   | ^^
+   |
+   = note: `#[deny(incomplete_include)]` on by default
+
+error: aborting due to previous error
+

src/tools/error_index_generator/build.rs

@@ -15,7 +15,7 @@ fn main() {
             println!("cargo:rerun-if-changed={}", entry.path().to_str().unwrap());
             let file = fs::read_to_string(entry.path()).unwrap()
                 .replace("syntax::register_diagnostics!", "register_diagnostics!");
-            let contents = format!("(|| {{\n{}\n}})();", file);
+            let contents = format!("(|| {{\n{}\n}})()", file);
 
             fs::write(&out_dir.join(&format!("error_{}.rs", idx)), &contents).unwrap();