[Fix] Update FlashInfer JIT header lookup

This PR fixes the tvm/dlpack/dmlc header lookup in the FlashInfer
kernel JIT compilation.

Prior to this fix, the JIT compilation assumes the environment
variable `TVM_SOURCE_DIR` is always defined, which is not always
true. This PR fixes the behavior and considers multiple cases,
including TVM source builds and pip-installed packages.

Author: MasterJH5574

python/tvm/libinfo.py

@@ -195,7 +195,9 @@ def find_include_path(name=None, search_path=None, optional=False):
     include_path : list(string)
         List of all found paths to header files.
     """
-    if os.environ.get("TVM_HOME", None):
+    if os.environ.get("TVM_SOURCE_DIR", None):
+        source_dir = os.environ["TVM_SOURCE_DIR"]
+    elif os.environ.get("TVM_HOME", None):
         source_dir = os.environ["TVM_HOME"]
     else:
         ffi_dir = os.path.dirname(os.path.abspath(os.path.expanduser(__file__)))
@@ -204,7 +206,7 @@ def find_include_path(name=None, search_path=None, optional=False):
             if os.path.isdir(os.path.join(source_dir, "include")):
                 break
         else:
-            raise AssertionError("Cannot find the source directory given ffi_dir: {ffi_dir}")
+            raise AssertionError(f"Cannot find the source directory given ffi_dir: {ffi_dir}")
     third_party_dir = os.path.join(source_dir, "3rdparty")
 
     header_path = []

python/tvm/relax/backend/cuda/flashinfer.py

@@ -124,17 +124,53 @@ def get_object_file_path(src: Path) -> Path:
     # ------------------------------------------------------------------------
     # 2) Include paths
     # ------------------------------------------------------------------------
-    tvm_home = os.environ["TVM_SOURCE_DIR"]
     include_paths = [
         FLASHINFER_INCLUDE_DIR,
         FLASHINFER_CSRC_DIR,
         FLASHINFER_TVM_BINDING_DIR,
-        Path(tvm_home).resolve() / "include",
-        Path(tvm_home).resolve() / "ffi" / "include",
-        Path(tvm_home).resolve() / "ffi" / "3rdparty" / "dlpack" / "include",
-        Path(tvm_home).resolve() / "3rdparty" / "dmlc-core" / "include",
     ] + CUTLASS_INCLUDE_DIRS
 
+    if os.environ.get("TVM_SOURCE_DIR", None) or os.environ.get("TVM_HOME", None):
+        # Respect TVM_SOURCE_DIR and TVM_HOME if they are set
+        tvm_home = (
+            os.environ["TVM_SOURCE_DIR"]
+            if os.environ.get("TVM_SOURCE_DIR", None)
+            else os.environ["TVM_HOME"]
+        )
+        include_paths += [
+            Path(tvm_home).resolve() / "include",
+            Path(tvm_home).resolve() / "ffi" / "include",
+            Path(tvm_home).resolve() / "ffi" / "3rdparty" / "dlpack" / "include",
+            Path(tvm_home).resolve() / "3rdparty" / "dmlc-core" / "include",
+        ]
+    else:
+        # If TVM_SOURCE_DIR and TVM_HOME are not set, use the default TVM package path
+        tvm_package_path = Path(tvm.__file__).resolve().parent
+        if (tvm_package_path / "include").exists():
+            # The package is installed from pip.
+            import tvm_ffi
+
+            tvm_ffi_package_path = Path(tvm_ffi.__file__).resolve().parent
+            include_paths += [
+                tvm_package_path / "include",
+                tvm_package_path / "3rdparty" / "dmlc-core" / "include",
+                tvm_ffi_package_path / "include",
+            ]
+        elif (tvm_package_path.parent.parent / "include").exists():
+            # The package is installed from source.
+            include_paths += [
+                tvm_package_path.parent.parent / "include",
+                tvm_package_path.parent.parent / "ffi" / "include",
+                tvm_package_path.parent.parent / "ffi" / "3rdparty" / "dlpack" / "include",
+                tvm_package_path.parent.parent / "3rdparty" / "dmlc-core" / "include",
+            ]
+        else:
+            # warning: TVM is not installed in the system.
+            print(
+                "Warning: Include path for TVM cannot be found. "
+                "FlashInfer kernel compilation may fail due to missing headers."
+            )
+
     # ------------------------------------------------------------------------
     # 3) Function to compile a single source file
     # ------------------------------------------------------------------------