Remember deopt-id -> context-level mappings in var descriptors.

runtime/vm/debugger.cc

Index: runtime/vm/debugger.cc
diff --git a/runtime/vm/debugger.cc b/runtime/vm/debugger.cc
index 4253eca091d89ff9a06aa966decee5ef35bafe84..ff3821a1f9929e237e999cb6865596d0299ae692 100644
--- a/runtime/vm/debugger.cc
+++ b/runtime/vm/debugger.cc
@@ -12,6 +12,7 @@
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
 #include "vm/deopt_instructions.h"
+#include "vm/disassembler.h"
 #include "vm/flags.h"
 #include "vm/globals.h"
 #include "vm/json_stream.h"
@@ -264,6 +265,7 @@ ActivationFrame::ActivationFrame(uword pc,
       token_pos_initialized_(false),
       token_pos_(TokenPosition::kNoSource),
       try_index_(-1),
+      deopt_id_(Thread::kNoDeoptId),
       line_number_(-1),
       column_number_(-1),
       context_level_(-1),
@@ -611,6 +613,7 @@ TokenPosition ActivationFrame::TokenPos() {
       if (iter.PcOffset() == pc_offset) {
         try_index_ = iter.TryIndex();
         token_pos_ = iter.TokenPos();
+        deopt_id_ = iter.DeoptId();
         break;
       }
     }
@@ -627,6 +630,14 @@ intptr_t ActivationFrame::TryIndex() {
 }
 
 
+intptr_t ActivationFrame::DeoptId() {
+  if (!token_pos_initialized_) {
+    TokenPos();  // Side effect: computes token_pos_initialized_, try_index_.
+  }
+  return deopt_id_;
+}
+
+
 intptr_t ActivationFrame::LineNumber() {
   // Compute line number lazily since it causes scanning of the script.
   if ((line_number_ < 0) && TokenPos().IsSourcePosition()) {
@@ -683,36 +694,45 @@ intptr_t ActivationFrame::ContextLevel() {
   const Context& ctx = GetSavedCurrentContext();
   if (context_level_ < 0 && !ctx.IsNull()) {
     ASSERT(!code_.is_optimized());
-    context_level_ = 0;
-    // TODO(hausner): What to do if there is no descriptor entry
-    // for the code position of the frame? For now say we are at context
-    // level 0.
-    TokenPos();
-    if (token_pos_ == TokenPosition::kNoSource) {
-      // No PcDescriptor.
-      return context_level_;
+
+    intptr_t deopt_id = DeoptId();
+    if (deopt_id == Thread::kNoDeoptId) {
+      DisassembleToStdout formatter;
+      code().Disassemble(&formatter);
+      PcDescriptors::Handle(code().pc_descriptors()).Print();
+      FATAL2("Missing deopt id for pc %" Px " in %s", pc_,
+             function().ToQualifiedCString());

[Vyacheslav Egorov (Google), 2017/06/01 12:32:41]

Maybe move this code to a helper function. 

Then on all FATAL errors in the debugger we can just call this function and get
the same level of details (e.g. deopt_id, pc, state of registers, disassembly).

[rmacnak, 2017/06/01 19:26:09]

Done like PrintContextMismatch.

     }
-    ASSERT(!pc_desc_.IsNull());
-    TokenPosition innermost_begin_pos = TokenPosition::kMinSource;
-    TokenPosition activation_token_pos = TokenPos().FromSynthetic();
-    ASSERT(activation_token_pos.IsReal());
     GetVarDescriptors();
     intptr_t var_desc_len = var_descriptors_.Length();
+    bool found = false;
     for (intptr_t cur_idx = 0; cur_idx < var_desc_len; cur_idx++) {
       RawLocalVarDescriptors::VarInfo var_info;
       var_descriptors_.GetInfo(cur_idx, &var_info);
       const int8_t kind = var_info.kind();
       if ((kind == RawLocalVarDescriptors::kContextLevel) &&
-          (var_info.begin_pos <= activation_token_pos) &&
-          (activation_token_pos < var_info.end_pos)) {
-        // This var_descriptors_ entry is a context scope which is in scope
-        // of the current token position. Now check whether it is shadowing
-        // the previous context scope.
-        if (innermost_begin_pos < var_info.begin_pos) {
-          innermost_begin_pos = var_info.begin_pos;
-          context_level_ = var_info.index();
-        }
+          (deopt_id >= var_info.begin_pos.value()) &&
+          (deopt_id <= var_info.end_pos.value())) {
+        context_level_ = var_info.index();
+        found = true;
+        break;
+      }
+    }
+    if (!found) {
+      DisassembleToStdout formatter;
+      code().Disassemble(&formatter);
+      PcDescriptors::Handle(code().pc_descriptors()).Print();
+
+      StackFrameIterator frames(StackFrameIterator::kDontValidateFrames,
+                                Thread::Current(),
+                                StackFrameIterator::kNoCrossThreadIteration);
+      StackFrame* frame = frames.NextFrame();
+      while (frame != NULL) {
+        OS::PrintErr("%s\n", frame->ToCString());
+        frame = frames.NextFrame();
       }
+      FATAL3("Missing context level for deopt_id=%" Pd ", pc=%" Px " in %s",
+             deopt_id, pc_, function().ToQualifiedCString());
     }
     ASSERT(context_level_ >= 0);
   }