pdb: Add AliasType support (LF_ALIAS/LF_ALIAS_ST)

Port of getsentry/pdb#134. Adds parsing for typedef/alias type records
which contain an underlying type index and a name.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kjk

pdb/src/index.ts

@@ -63,6 +63,7 @@ export type {
   PointerType,
   ModifierType,
   ArrayType,
+  AliasType,
   BitfieldType,
   FieldListType,
   ArgumentListType,

pdb/src/tpi/constants.ts

@@ -40,6 +40,7 @@ export const LF_ENUM_ST = 0x1007;
 export const LF_PROCEDURE = 0x1008;
 export const LF_MFUNCTION = 0x1009;
 export const LF_COBOL0 = 0x100a;
+export const LF_ALIAS_ST = 0x1010;
 export const LF_BARRAY = 0x100b;
 export const LF_VFTPATH = 0x100d;
 

pdb/src/tpi/parser.ts

@@ -303,6 +303,13 @@ function parseTypeRecord(buf: ParseBuffer, kind: number): TypeData {
       };
     }
 
+    case C.LF_ALIAS:
+    case C.LF_ALIAS_ST: {
+      const underlyingType: TypeIndex = buf.readU32();
+      const name = readTypeName(buf, kind);
+      return { kind: "Alias", underlyingType, name };
+    }
+
     case C.LF_BITFIELD: {
       const underlyingType: TypeIndex = buf.readU32();
       const length = buf.readU8();

pdb/src/tpi/types.ts

@@ -271,6 +271,12 @@ export interface ArrayType {
   name: string;
 }
 
+export interface AliasType {
+  kind: "Alias";
+  underlyingType: TypeIndex;
+  name: string;
+}
+
 export interface BitfieldType {
   kind: "Bitfield";
   underlyingType: TypeIndex;
@@ -387,6 +393,7 @@ export type TypeData =
   | PointerType
   | ModifierType
   | ArrayType
+  | AliasType
   | BitfieldType
   | FieldListType
   | ArgumentListType