Address review comments

- Update the documentation and doc-comments
- Improve the error message for parsing Cargo.toml

src/cargo/core/profiles.rs

@@ -762,7 +762,7 @@ impl DebugInfo {
         }
     }
 
-    /// Returns true if the debuginfo level is high enough (at least 1). Helper
+    /// Returns true if any debuginfo will be generated. Helper
     /// for a common operation on the usual `Option` representation.
     pub(crate) fn is_turned_on(&self) -> bool {
         !matches!(self.to_option(), None | Some(TomlDebugInfo::None))

src/cargo/util/toml/mod.rs

@@ -478,7 +478,7 @@ impl<'de> de::Deserialize<'de> for TomlDebugInfo {
 
             fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
                 formatter
-                    .write_str("a boolean, 0-2, \"line-tables-only\", or \"line-directives-only\"")
+                    .write_str("a boolean, 0, 1, 2, \"line-tables-only\", or \"line-directives-only\"")
             }
 
             fn visit_i64<E>(self, value: i64) -> Result<TomlDebugInfo, E>

src/doc/src/reference/profiles.md

@@ -67,9 +67,11 @@ amount of debug information included in the compiled binary.
 
 The valid options are:
 
-* `0` or `false`: no debug info at all
-* `1`: line tables only
-* `2` or `true`: full debug info
+* `0`, `false`, or `"none"`: no debug info at all
+* `"line-directives-only"`: line info directives only. For the nvptx* targets this enables [profiling](https://reviews.llvm.org/D46061). For other use cases, `line-tables-only` is the better, more compatible choice.
+* `"line-tables-only"`: line tables only. Generates the minimal amount of debug info for backtraces with filename/line number info, but not anything else, i.e. no variable or function parameter info.
+* `1` or `"limited"`: debug info without type or variable-level information. Generates more detailed module-level info than `line-tables-only`.
+* `2`, `true`, or `"full"`: full debug info
 
 You may wish to also configure the [`split-debuginfo`](#split-debuginfo) option
 depending on your needs as well.