From 41856b0a0f0a612c1e64088baed5389d82f93157 Mon Sep 17 00:00:00 2001
From: Ezra Shaw <ezrasure@outlook.com>
Date: Sat, 14 Jan 2023 23:00:17 +1300
Subject: [PATCH] allow negative numeric literals in `concat!`

---
 compiler/rustc_builtin_macros/src/concat.rs | 15 ++++++++++++++-
 tests/ui/macros/bad-concat.stderr           |  2 +-
 tests/ui/macros/concat.stderr               |  4 ++--
 tests/ui/macros/issue-106837.rs             | 10 ++++++++++
 tests/ui/macros/issue-106837.stderr         | 18 ++++++++++++++++++
 5 files changed, 45 insertions(+), 4 deletions(-)
 create mode 100644 tests/ui/macros/issue-106837.rs
 create mode 100644 tests/ui/macros/issue-106837.stderr

diff --git a/compiler/rustc_builtin_macros/src/concat.rs b/compiler/rustc_builtin_macros/src/concat.rs
index 7da9bdc38a2a8..36682bbe0708f 100644
--- a/compiler/rustc_builtin_macros/src/concat.rs
+++ b/compiler/rustc_builtin_macros/src/concat.rs
@@ -42,6 +42,18 @@ pub fn expand_concat(
                     has_errors = true;
                 }
             },
+            // We also want to allow negative numeric literals.
+            ast::ExprKind::Unary(ast::UnOp::Neg, ref expr) if let ast::ExprKind::Lit(token_lit) = expr.kind => {
+                match ast::LitKind::from_token_lit(token_lit) {
+                    Ok(ast::LitKind::Int(i, _)) => accumulator.push_str(&format!("-{i}")),
+                    Ok(ast::LitKind::Float(f, _)) => accumulator.push_str(&format!("-{f}")),
+                    Err(err) => {
+                        report_lit_error(&cx.sess.parse_sess, err, token_lit, e.span);
+                        has_errors = true;
+                    }
+                    _ => missing_literal.push(e.span),
+                }
+            }
             ast::ExprKind::IncludedBytes(..) => {
                 cx.span_err(e.span, "cannot concatenate a byte string literal")
             }
@@ -53,9 +65,10 @@ pub fn expand_concat(
             }
         }
     }
+
     if !missing_literal.is_empty() {
         let mut err = cx.struct_span_err(missing_literal, "expected a literal");
-        err.note("only literals (like `\"foo\"`, `42` and `3.14`) can be passed to `concat!()`");
+        err.note("only literals (like `\"foo\"`, `-42` and `3.14`) can be passed to `concat!()`");
         err.emit();
         return DummyResult::any(sp);
     } else if has_errors {
diff --git a/tests/ui/macros/bad-concat.stderr b/tests/ui/macros/bad-concat.stderr
index 4316fd312c739..d67f3c33d36e3 100644
--- a/tests/ui/macros/bad-concat.stderr
+++ b/tests/ui/macros/bad-concat.stderr
@@ -4,7 +4,7 @@ error: expected a literal
 LL |     let _ = concat!(x, y, z, "bar");
    |                     ^  ^  ^
    |
-   = note: only literals (like `"foo"`, `42` and `3.14`) can be passed to `concat!()`
+   = note: only literals (like `"foo"`, `-42` and `3.14`) can be passed to `concat!()`
 
 error: aborting due to previous error
 
diff --git a/tests/ui/macros/concat.stderr b/tests/ui/macros/concat.stderr
index 61fb9de1ef96c..d65d9354454c3 100644
--- a/tests/ui/macros/concat.stderr
+++ b/tests/ui/macros/concat.stderr
@@ -16,7 +16,7 @@ error: expected a literal
 LL |     concat!(foo);
    |             ^^^
    |
-   = note: only literals (like `"foo"`, `42` and `3.14`) can be passed to `concat!()`
+   = note: only literals (like `"foo"`, `-42` and `3.14`) can be passed to `concat!()`
 
 error: expected a literal
   --> $DIR/concat.rs:5:13
@@ -24,7 +24,7 @@ error: expected a literal
 LL |     concat!(foo());
    |             ^^^^^
    |
-   = note: only literals (like `"foo"`, `42` and `3.14`) can be passed to `concat!()`
+   = note: only literals (like `"foo"`, `-42` and `3.14`) can be passed to `concat!()`
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/macros/issue-106837.rs b/tests/ui/macros/issue-106837.rs
new file mode 100644
index 0000000000000..7bbd3d68a900e
--- /dev/null
+++ b/tests/ui/macros/issue-106837.rs
@@ -0,0 +1,10 @@
+fn main() {
+    concat!(-42);
+    concat!(-3.14);
+
+    concat!(-"hello");
+    //~^ ERROR expected a literal
+
+    concat!(--1);
+    //~^ ERROR expected a literal
+}
diff --git a/tests/ui/macros/issue-106837.stderr b/tests/ui/macros/issue-106837.stderr
new file mode 100644
index 0000000000000..998d6c5eb6f2b
--- /dev/null
+++ b/tests/ui/macros/issue-106837.stderr
@@ -0,0 +1,18 @@
+error: expected a literal
+  --> $DIR/issue-106837.rs:5:13
+   |
+LL |     concat!(-"hello");
+   |             ^^^^^^^^
+   |
+   = note: only literals (like `"foo"`, `-42` and `3.14`) can be passed to `concat!()`
+
+error: expected a literal
+  --> $DIR/issue-106837.rs:8:13
+   |
+LL |     concat!(--1);
+   |             ^^^
+   |
+   = note: only literals (like `"foo"`, `-42` and `3.14`) can be passed to `concat!()`
+
+error: aborting due to 2 previous errors
+