From a2a4adf877159c224571d906cd0c8f431c44a3b7 Mon Sep 17 00:00:00 2001
From: jackohoeg <jackohoeg@gmail.com>
Date: Wed, 17 May 2023 12:01:26 -0400
Subject: [PATCH] Correct 'usdcat --flattenLayerStack' which had been
 outputting a flattened, unloaded stage.

---
 pxr/usd/bin/usdcat/CMakeLists.txt             | 16 ++++++++++++++++
 .../baseline/output.usda                      |  9 +++++++++
 .../testenv/testFlattenLayerStack/input.usda  | 12 ++++++++++++
 .../testFlattenLayerStack/sublayer.usda       |  5 +++++
 pxr/usd/bin/usdcat/usdcat.cpp                 | 19 +++++++++++--------
 5 files changed, 53 insertions(+), 8 deletions(-)
 create mode 100644 pxr/usd/bin/usdcat/testenv/testFlattenLayerStack/baseline/output.usda
 create mode 100644 pxr/usd/bin/usdcat/testenv/testFlattenLayerStack/input.usda
 create mode 100644 pxr/usd/bin/usdcat/testenv/testFlattenLayerStack/sublayer.usda

diff --git a/pxr/usd/bin/usdcat/CMakeLists.txt b/pxr/usd/bin/usdcat/CMakeLists.txt
index 5d3d216091..73c4606377 100644
--- a/pxr/usd/bin/usdcat/CMakeLists.txt
+++ b/pxr/usd/bin/usdcat/CMakeLists.txt
@@ -50,6 +50,11 @@ pxr_register_test(testUsdCatMissingOrInvalidFiles2
     EXPECTED_RETURN_CODE 1 
 )
 
+pxr_register_test(testUsdCatMissingOrInvalidFiles3
+    COMMAND "${CMAKE_INSTALL_PREFIX}/bin/usdcat --flattenLayerStack foo.usda"
+    EXPECTED_RETURN_CODE 1
+)
+
 pxr_install_test_dir(
     SRC testenv/testUsdCatMask
     DEST testUsdCatMask
@@ -86,3 +91,14 @@ pxr_register_test(testUsdCatLayerMetadata
     DIFF_COMPARE output.usda
     EXPECTED_RETURN_CODE 0
 )
+
+pxr_install_test_dir(
+    SRC testenv/testFlattenLayerStack
+    DEST testUsdCatFlattenLayerStack
+)
+
+pxr_register_test(testUsdCatFlattenLayerStack
+    COMMAND "${CMAKE_INSTALL_PREFIX}/bin/usdcat --flattenLayerStack input.usda --out output.usda"
+    DIFF_COMPARE output.usda
+    EXPECTED_RETURN_CODE 0
+)
diff --git a/pxr/usd/bin/usdcat/testenv/testFlattenLayerStack/baseline/output.usda b/pxr/usd/bin/usdcat/testenv/testFlattenLayerStack/baseline/output.usda
new file mode 100644
index 0000000000..ddd11a6c88
--- /dev/null
+++ b/pxr/usd/bin/usdcat/testenv/testFlattenLayerStack/baseline/output.usda
@@ -0,0 +1,9 @@
+#usda 1.0
+
+def Xform "Prim" (
+    references = @reference.usda@</Prim>
+)
+{
+    int primvars:should_be_here = 0
+}
+
diff --git a/pxr/usd/bin/usdcat/testenv/testFlattenLayerStack/input.usda b/pxr/usd/bin/usdcat/testenv/testFlattenLayerStack/input.usda
new file mode 100644
index 0000000000..d0d7560526
--- /dev/null
+++ b/pxr/usd/bin/usdcat/testenv/testFlattenLayerStack/input.usda
@@ -0,0 +1,12 @@
+#usda 1.0
+(
+    subLayers = [
+        @./sublayer.usda@
+    ]
+)
+
+over "Prim" (
+    references = @reference.usda@</Prim>
+)
+{
+}
diff --git a/pxr/usd/bin/usdcat/testenv/testFlattenLayerStack/sublayer.usda b/pxr/usd/bin/usdcat/testenv/testFlattenLayerStack/sublayer.usda
new file mode 100644
index 0000000000..56e42f6516
--- /dev/null
+++ b/pxr/usd/bin/usdcat/testenv/testFlattenLayerStack/sublayer.usda
@@ -0,0 +1,5 @@
+#usda 1.0
+
+def Xform "Prim" {
+    int primvars:should_be_here = 0
+}
diff --git a/pxr/usd/bin/usdcat/usdcat.cpp b/pxr/usd/bin/usdcat/usdcat.cpp
index 79b70693a9..21ef6c7690 100644
--- a/pxr/usd/bin/usdcat/usdcat.cpp
+++ b/pxr/usd/bin/usdcat/usdcat.cpp
@@ -216,7 +216,9 @@ static int UsdCat(const Args &args) {
             }
         } else if (args.flattenLayerStack) {
             stage = UsdStage::Open(input, UsdStage::LoadNone);
-            layer = UsdUtilsFlattenLayerStack(stage);
+            if (stage) {
+                layer = UsdUtilsFlattenLayerStack(stage);
+            }
         } else if (args.layerMetadata) {
             auto srcLayer = SdfLayer::OpenAsAnonymous(
                 input, /* metadataOnly = */ true);
@@ -263,13 +265,13 @@ static int UsdCat(const Args &args) {
 
         // Write to either stdout or the specified output file
         if (!args.output.empty()) {
-            if (stage) {
+            if (layer) {
+                layer->Export(args.output, std::string(), formatArgs);
+            }
+            else {
                 stage->Export(
                     args.output, !args.skipSourceFileComment, formatArgs);
             }
-            else if (layer) {
-                layer->Export(args.output, std::string(), formatArgs);
-            }
 
             if (!errMark.IsClean()) {
                 exitCode = 1;
@@ -288,11 +290,12 @@ static int UsdCat(const Args &args) {
         }
         else {
             std::string usdString;
-            if (stage) {
-                stage->ExportToString(&usdString);
-            } else {
+            if (layer) {
                 layer->ExportToString(&usdString);
             }
+            else {
+                stage->ExportToString(&usdString);
+            }
 
             if (errMark.IsClean()) {
                 std::cout << usdString;