Merge pull request #9677 from swiftlang/dl/lldb-Update-dwim-print-to-support-limited-variable-expression-paths-117452

[lldb] Update dwim-print to support limited variable expression paths

Author: adrian-prantl

lldb/source/Commands/CommandObjectDWIMPrint.cpp

@@ -153,10 +153,24 @@ void CommandObjectDWIMPrint::DoExecute(StringRef command,
     result.SetStatus(eReturnStatusSuccessFinishResult);
   };
 
-  // First, try `expr` as the name of a frame variable.
-  if (frame) {
-    auto valobj_sp = frame->FindVariable(ConstString(expr));
-    if (valobj_sp && valobj_sp->GetError().Success()) {
+  // First, try `expr` as a _limited_ frame variable expression path: only the
+  // dot operator (`.`) is permitted for this case.
+  //
+  // This is limited to support only unambiguous expression paths. Of note,
+  // expression paths are not attempted if the expression contain either the
+  // arrow operator (`->`) or the subscript operator (`[]`). This is because
+  // both operators can be overloaded in C++, and could result in ambiguity in
+  // how the expression is handled. Additionally, `*` and `&` are not supported.
+  const bool try_variable_path =
+      expr.find_first_of("*&->[]") == StringRef::npos;
+  if (frame && try_variable_path) {
+    VariableSP var_sp;
+    Status status;
+    auto valobj_sp = frame->GetValueForVariableExpressionPath(
+        expr, eval_options.GetUseDynamic(),
+        StackFrame::eExpressionPathOptionsAllowDirectIVarAccess, var_sp,
+        status);
+    if (valobj_sp && status.Success() && valobj_sp->GetError().Success()) {
       if (!suppress_result) {
         if (auto persisted_valobj = valobj_sp->Persist())
           valobj_sp = persisted_valobj;

lldb/test/API/commands/dwim-print/Makefile

@@ -1,3 +1,3 @@
-C_SOURCES := main.c
+CXX_SOURCES := main.cpp
 
 include Makefile.rules

lldb/test/API/commands/dwim-print/TestDWIMPrint.py

@@ -16,7 +16,7 @@ def _run_cmd(self, cmd: str) -> str:
         self.ci.HandleCommand(cmd, result)
         return result.GetOutput().rstrip()
 
-    VAR_IDENT = re.compile(r"(?:\$\d+|\w+) = ")
+    VAR_IDENT = re.compile(r"(?:\$\d+|[\w.]+) = ")
 
     def _strip_result_var(self, string: str) -> str:
         """
@@ -121,30 +121,39 @@ def test_empty_expression(self):
     def test_nested_values(self):
         """Test dwim-print with nested values (structs, etc)."""
         self.build()
-        lldbutil.run_to_source_breakpoint(self, "break here", lldb.SBFileSpec("main.c"))
+        lldbutil.run_to_source_breakpoint(
+            self, "break here", lldb.SBFileSpec("main.cpp")
+        )
         self.runCmd("settings set auto-one-line-summaries false")
         self._expect_cmd(f"dwim-print s", "frame variable")
         self._expect_cmd(f"dwim-print (struct Structure)s", "expression")
 
     def test_summary_strings(self):
-        """Test dwim-print with nested values (structs, etc)."""
+        """Test dwim-print with type summaries."""
         self.build()
-        lldbutil.run_to_source_breakpoint(self, "break here", lldb.SBFileSpec("main.c"))
+        lldbutil.run_to_source_breakpoint(
+            self, "break here", lldb.SBFileSpec("main.cpp")
+        )
         self.runCmd("settings set auto-one-line-summaries false")
         self.runCmd("type summary add -e -s 'stub summary' Structure")
         self._expect_cmd(f"dwim-print s", "frame variable")
         self._expect_cmd(f"dwim-print (struct Structure)s", "expression")
+        self.runCmd("type summary delete Structure")
 
     def test_void_result(self):
         """Test dwim-print does not surface an error message for void expressions."""
         self.build()
-        lldbutil.run_to_source_breakpoint(self, "break here", lldb.SBFileSpec("main.c"))
+        lldbutil.run_to_source_breakpoint(
+            self, "break here", lldb.SBFileSpec("main.cpp")
+        )
         self.expect("dwim-print (void)15", matching=False, patterns=["(?i)error"])
 
     def test_preserves_persistent_variables(self):
         """Test dwim-print does not delete persistent variables."""
         self.build()
-        lldbutil.run_to_source_breakpoint(self, "break here", lldb.SBFileSpec("main.c"))
+        lldbutil.run_to_source_breakpoint(
+            self, "break here", lldb.SBFileSpec("main.cpp")
+        )
         self.expect("dwim-print int $i = 15")
         # Run the same expression twice and verify success. This ensures the
         # first command does not delete the persistent variable.
@@ -154,5 +163,25 @@ def test_preserves_persistent_variables(self):
     def test_missing_type(self):
         """The expected output of po opaque is its address (no error)"""
         self.build()
-        lldbutil.run_to_source_breakpoint(self, "break here", lldb.SBFileSpec("main.c"))
+        lldbutil.run_to_source_breakpoint(
+            self, "break here", lldb.SBFileSpec("main.cpp")
+        )
         self.expect("dwim-print -O -- opaque", substrs=["0x"])
+
+    def test_variable_expression_path(self):
+        """Test dwim-print supports certain variable expression paths."""
+        self.build()
+        lldbutil.run_to_source_breakpoint(
+            self, "break here", lldb.SBFileSpec("main.cpp")
+        )
+        self.runCmd("settings set auto-one-line-summaries false")
+        self._expect_cmd("dwim-print w.s", "frame variable")
+        self._expect_cmd("dwim-print wp->s", "expression")
+
+    def test_direct_child_access(self):
+        """Test dwim-print supports accessing members/ivars without qualification."""
+        self.build()
+        lldbutil.run_to_source_breakpoint(
+            self, "break inside", lldb.SBFileSpec("main.cpp")
+        )
+        self._expect_cmd("dwim-print number", "frame variable")

lldb/test/API/commands/dwim-print/main.c

@@ -0,0 +1,22 @@
+extern "C" int puts(const char *s);
+
+struct Structure {
+  int number = 30;
+  void f() { puts("break inside"); }
+};
+
+struct Wrapper {
+  Structure s;
+};
+
+struct Opaque;
+
+int main(int argc, char **argv) {
+  Structure s;
+  Wrapper w;
+  Wrapper *wp = &w;
+  Opaque *opaque = (Opaque *)(void *)&s;
+  puts("break here");
+  s.f();
+  return 0;
+}

lldb/test/API/commands/dwim-print/main.cpp

@@ -56,5 +56,5 @@ def check(value):
                     substrs=['Missing type'])
 
         process.Continue()
-        self.expect('dwim-print -O -- number', error=True,
+        self.expect('expression -O -- number', error=True,
                     substrs=['self', 'not', 'found'])