[llvm-lib][llvm-dlltool] Fix handling of invalid ARM64EC function names (#116250)

This is a follow-up to #115567. Emit an error for invalid function
names, similar to MSVC's `lib.exe` behavior.

Returning an error from `writeImportLibrary` exposed bugs in error
handling by its callers, which have been addressed in this patch.

llvm/lib/Object/COFFImportFile.cpp

@@ -756,8 +756,15 @@ Error writeImportLibrary(StringRef ImportName, StringRef Path,
           }
           Name = std::move(*MangledName);
         } else if (!E.Noname && ExportName.empty()) {
+          std::optional<std::string> DemangledName =
+              getArm64ECDemangledFunctionName(Name);
+          if (!DemangledName)
+            return make_error<StringError>(
+                StringRef(Twine("Invalid ARM64EC function name '" + Name + "'")
+                              .str()),
+                object_error::parse_failed);
           NameType = IMPORT_NAME_EXPORTAS;
-          ExportName = std::move(*getArm64ECDemangledFunctionName(Name));
+          ExportName = std::move(*DemangledName);
         }
       }
 

llvm/lib/ToolDrivers/llvm-dlltool/DlltoolDriver.cpp

@@ -243,8 +243,14 @@ int llvm::dlltoolDriverMain(llvm::ArrayRef<const char *> ArgsArr) {
   }
 
   std::string Path = std::string(Args.getLastArgValue(OPT_l));
-  if (!Path.empty() && writeImportLibrary(OutputFile, Path, Exports, Machine,
-                                          /*MinGW=*/true, NativeExports))
-    return 1;
+  if (!Path.empty()) {
+    if (Error E = writeImportLibrary(OutputFile, Path, Exports, Machine,
+                                     /*MinGW=*/true, NativeExports)) {
+      handleAllErrors(std::move(E), [&](const ErrorInfoBase &EI) {
+        llvm::errs() << EI.message() << "\n";
+      });
+      return 1;
+    }
+  }
   return 0;
 }

llvm/lib/ToolDrivers/llvm-lib/LibDriver.cpp

@@ -419,10 +419,15 @@ int llvm::libDriverMain(ArrayRef<const char *> ArgsArr) {
       OutputFile = std::move(NativeDef->OutputFile);
     }
 
-    return writeImportLibrary(OutputFile, OutputPath, Def->Exports, LibMachine,
-                              /*MinGW=*/false, NativeExports)
-               ? 1
-               : 0;
+    if (Error E =
+            writeImportLibrary(OutputFile, OutputPath, Def->Exports, LibMachine,
+                               /*MinGW=*/false, NativeExports)) {
+      handleAllErrors(std::move(E), [&](const ErrorInfoBase &EI) {
+        llvm::errs() << OutputPath << ": " << EI.message() << "\n";
+      });
+      return 1;
+    }
+    return 0;
   }
 
   // If no input files and not told otherwise, silently do nothing to match

llvm/test/tools/llvm-dlltool/arm64ec-invalid-name.test

@@ -0,0 +1,6 @@
+; RUN: not llvm-dlltool -m arm64ec -d %s -l %t.lib 2>&1 | FileCheck %s
+; CHECK: Invalid ARM64EC function name '?func'
+
+LIBRARY test.dll
+EXPORTS
+        ?func

llvm/test/tools/llvm-lib/arm64ec-invalid-name.test

@@ -0,0 +1,6 @@
+; RUN: not llvm-lib -machine:arm64ec -def:%s -out:%t.lib 2>&1 | FileCheck %s
+; CHECK: Invalid ARM64EC function name '?func'
+
+LIBRARY test.dll
+EXPORTS
+        ?func