Auto merge of #13375 - epage:panic, r=Muscraft

fix(diagnostic): Don't panic on empty spans

### What does this PR try to resolve?

There is another level to this bug where we better point to where the
error occurs, see toml-rs/toml#669.

Fixes #13374

### How should we test and review this PR?

### Additional information

Author: bors

src/cargo/util/toml/mod.rs

@@ -121,7 +121,7 @@ fn read_manifest_from_str(
                 .rfind('\n')
                 .map(|s| s + 1)
                 .unwrap_or(0);
-            let source_end = contents[span.end - 1..]
+            let source_end = contents[span.end.saturating_sub(1)..]
                 .find('\n')
                 .map(|s| s + span.end)
                 .unwrap_or(contents.len());

tests/testsuite/diagnostics.rs

@@ -0,0 +1,30 @@
+use cargo_test_support::project;
+
+#[cargo_test]
+fn dont_panic_on_render() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+[package]
+name = "foo"
+version = "0.1.0"
+edition = "2021"
+[[bench.foo]]
+"#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("check")
+        .with_status(101)
+        .with_stderr(
+            "\
+error: invalid type: map, expected a sequence
+--> Cargo.toml:1:1
+ |
+ |
+",
+        )
+        .run();
+}

tests/testsuite/main.rs

@@ -79,6 +79,7 @@ mod cross_publish;
 mod custom_target;
 mod death;
 mod dep_info;
+mod diagnostics;
 mod direct_minimal_versions;
 mod directory;
 mod doc;