compiler: Support nightly -Cforce-frame-pointers=non-leaf

Requires -Zunstable-options as this is a -C flag already.

compiler/rustc_session/src/config.rs

@@ -19,7 +19,7 @@ use rustc_macros::{Decodable, Encodable, HashStable_Generic};
 use rustc_span::edition::{Edition, DEFAULT_EDITION, EDITION_NAME_LIST, LATEST_STABLE_EDITION};
 use rustc_span::source_map::FilePathMapping;
 use rustc_span::{FileName, FileNameDisplayPreference, RealFileName, SourceFileHashAlgorithm};
-use rustc_target::spec::{LinkSelfContainedComponents, LinkerFeatures};
+use rustc_target::spec::{FramePointer, LinkSelfContainedComponents, LinkerFeatures};
 use rustc_target::spec::{SplitDebuginfo, Target, TargetTriple};
 use std::collections::btree_map::{
     Iter as BTreeMapIter, Keys as BTreeMapKeysIter, Values as BTreeMapValuesIter,
@@ -2468,6 +2468,15 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
         }
     }
 
+    if !nightly_options::is_unstable_enabled(matches)
+        && cg.force_frame_pointers == FramePointer::NonLeaf
+    {
+        early_dcx.early_fatal(
+            "`-Cforce-frame-pointers=non-leaf` also requires `-Zunstable-options` \
+                and a nightly compiler",
+        )
+    }
+
     // For testing purposes, until we have more feedback about these options: ensure `-Z
     // unstable-options` is required when using the unstable `-C link-self-contained` and `-C
     // linker-flavor` options.

compiler/rustc_session/src/options.rs

@@ -373,7 +373,8 @@ mod desc {
     pub const parse_opt_comma_list: &str = parse_comma_list;
     pub const parse_number: &str = "a number";
     pub const parse_opt_number: &str = parse_number;
-    pub const parse_frame_pointer: &str = parse_bool;
+    pub const parse_frame_pointer: &str =
+        "one of `true`/`yes`/`on`, `false`/`no`/`off`, or (with -Zunstable-options) `non-leaf`";
     pub const parse_threads: &str = parse_number;
     pub const parse_time_passes_format: &str = "`text` (default) or `json`";
     pub const parse_passes: &str = "a space-separated list of passes, or `all`";
@@ -675,9 +676,9 @@ mod parse {
         let mut is_parsed = parse_bool(&mut boolish, v);
         if boolish & is_parsed {
             *slot = FramePointer::Always;
-        } else if false {
-            /* TODO: add NonLeaf as an unstable opt */
+        } else if v == Some("non-leaf") {
             is_parsed = true;
+            *slot = FramePointer::NonLeaf;
         };
         is_parsed
     }