gdb/lldb: Trim output of vec/slice/array

Fix rust-lang#29467

Author: untitaker

src/etc/gdb_rust_pretty_printing.py

@@ -209,15 +209,12 @@ def to_string(self):
                 ("(len: %i)" % length))
 
     def children(self):
-        cs = []
         (length, data_ptr) = rustpp.extract_length_and_ptr_from_slice(self.__val)
+
         assert data_ptr.type.get_dwarf_type_kind() == rustpp.DWARF_TYPE_CODE_PTR
         raw_ptr = data_ptr.get_wrapped_value()
 
-        for index in range(0, length):
-            cs.append((str(index), (raw_ptr + index).dereference()))
-
-        return cs
+        return iter_children_pointer(raw_ptr, length)
 
 
 class RustStringSlicePrinter:
@@ -243,12 +240,9 @@ def to_string(self):
                 ("(len: %i, cap: %i)" % (length, cap)))
 
     def children(self):
-        cs = []
         (length, data_ptr, cap) = rustpp.extract_length_ptr_and_cap_from_std_vec(self.__val)
-        gdb_ptr = data_ptr.get_wrapped_value()
-        for index in range(0, length):
-            cs.append((str(index), (gdb_ptr + index).dereference()))
-        return cs
+        raw_ptr = data_ptr.get_wrapped_value()
+        return iter_children_pointer(raw_ptr, length)
 
 
 class RustStdStringPrinter:
@@ -286,3 +280,7 @@ def get_field_at_index(gdb_val, index):
             return field
         i += 1
     return None
+
+def iter_children_pointer(raw_ptr, length):
+    for index in range(0, length):
+        yield str(index), (raw_ptr + index).dereference()

src/etc/lldb_rust_formatters.py

@@ -12,6 +12,9 @@
 import re
 import debugger_pretty_printers_common as rustpp
 
+# Maximal amount of array/vec/slice items to print before trimming
+MAX_CHILDREN = 100
+
 #===============================================================================
 # LLDB Pretty Printing Module for Rust
 #===============================================================================
@@ -311,7 +314,18 @@ def render_element(i):
                                                        element_type)
         return print_val(element_val, internal_dict)
 
-    return ', '.join([render_element(i) for i in range(length)])
+    overflow = length > MAX_CHILDREN
+    if overflow:
+        length = MAX_CHILDREN
+
+    def render_all():
+        for i in range(length):
+            yield render_element(i)
+
+        if overflow:
+            yield ".."
+
+    return ', '.join(render_all())
 
 
 def read_utf8_string(ptr_val, byte_count):