Add symbol kind and structured flags to diff proto output (#337)

* Add symbol kind to diff proto output

Expose SymbolKind (Function, Object, Section, Unknown) in the
DiffSymbol proto message, allowing CLI oneshot diff consumers to
distinguish symbol types without inferring from instruction/data
presence.

* Stop filtering symbols from diff output, replace flags bitmask with message

Remove the symbol filter (size == 0 / Ignored) from DiffObject so all
symbols are emitted. This fixes target_symbol indices being invalid
after filtering.

Replace the DiffSymbolFlag bitmask enum + uint32 field with a
DiffSymbolFlags message of booleans, adding ignored and size_inferred
flags so consumers can filter on their end.

objdiff-core/protos/diff.proto

@@ -39,7 +39,8 @@ message DiffSymbol {
   optional string demangled_name = 2;
   uint64 address = 3;
   uint64 size = 4;
-  uint32 flags = 5;
+  DiffSymbolFlags flags = 5;
+  DiffSymbolKind kind = 10;
   // The symbol index in the _other_ object that this symbol was diffed against
   optional uint32 target_symbol = 6;
   optional float match_percent = 7;
@@ -49,14 +50,22 @@ message DiffSymbol {
   repeated DiffDataSegment data_diff = 9;
 }
 
-// Symbol visibility flags (bitmask)
-enum DiffSymbolFlag {
-  SYMBOL_NONE = 0;
-  SYMBOL_GLOBAL = 1;
-  SYMBOL_LOCAL = 2;
-  SYMBOL_WEAK = 4;
-  SYMBOL_COMMON = 8;
-  SYMBOL_HIDDEN = 16;
+enum DiffSymbolKind {
+  SYMBOL_UNKNOWN = 0;
+  SYMBOL_FUNCTION = 1;
+  SYMBOL_OBJECT = 2;
+  SYMBOL_SECTION = 3;
+}
+
+// Symbol flags
+message DiffSymbolFlags {
+  bool global = 1;
+  bool local = 2;
+  bool weak = 3;
+  bool common = 4;
+  bool hidden = 5;
+  bool ignored = 6;
+  bool size_inferred = 7;
 }
 
 // A single instruction diff row

objdiff-core/src/bindings/diff.rs

@@ -43,9 +43,6 @@ impl DiffObject {
         let mut symbols = Vec::with_capacity(obj.symbols.len());
         for (symbol_idx, symbol) in obj.symbols.iter().enumerate() {
             let symbol_diff = &diff.symbols[symbol_idx];
-            if symbol.size == 0 || symbol.flags.contains(SymbolFlag::Ignored) {
-                continue;
-            }
             symbols.push(DiffSymbol::new(obj, symbol_idx, symbol, symbol_diff, diff_config)?);
         }
 
@@ -112,6 +109,7 @@ impl DiffSymbol {
             address: symbol.address,
             size: symbol.size,
             flags: symbol_flags(&symbol.flags),
+            kind: DiffSymbolKind::from(symbol.kind) as i32,
             // Diff information
             target_symbol: symbol_diff.target_symbol.map(|i| i as u32),
             match_percent: symbol_diff.match_percent,
@@ -121,24 +119,27 @@ impl DiffSymbol {
     }
 }
 
-fn symbol_flags(flags: &obj::SymbolFlagSet) -> u32 {
-    let mut result = 0u32;
-    if flags.contains(SymbolFlag::Global) {
-        result |= DiffSymbolFlag::SymbolGlobal as u32;
+impl From<obj::SymbolKind> for DiffSymbolKind {
+    fn from(value: obj::SymbolKind) -> Self {
+        match value {
+            obj::SymbolKind::Unknown => DiffSymbolKind::SymbolUnknown,
+            obj::SymbolKind::Function => DiffSymbolKind::SymbolFunction,
+            obj::SymbolKind::Object => DiffSymbolKind::SymbolObject,
+            obj::SymbolKind::Section => DiffSymbolKind::SymbolSection,
+        }
     }
-    if flags.contains(SymbolFlag::Local) {
-        result |= DiffSymbolFlag::SymbolLocal as u32;
-    }
-    if flags.contains(SymbolFlag::Weak) {
-        result |= DiffSymbolFlag::SymbolWeak as u32;
-    }
-    if flags.contains(SymbolFlag::Common) {
-        result |= DiffSymbolFlag::SymbolCommon as u32;
-    }
-    if flags.contains(SymbolFlag::Hidden) {
-        result |= DiffSymbolFlag::SymbolHidden as u32;
-    }
-    result
+}
+
+fn symbol_flags(flags: &obj::SymbolFlagSet) -> Option<DiffSymbolFlags> {
+    Some(DiffSymbolFlags {
+        global: flags.contains(SymbolFlag::Global),
+        local: flags.contains(SymbolFlag::Local),
+        weak: flags.contains(SymbolFlag::Weak),
+        common: flags.contains(SymbolFlag::Common),
+        hidden: flags.contains(SymbolFlag::Hidden),
+        ignored: flags.contains(SymbolFlag::Ignored),
+        size_inferred: flags.contains(SymbolFlag::SizeInferred),
+    })
 }
 
 impl DiffInstructionRow {