[lldb] Inline expression evaluator error visualization (#106470)

This patch is a reworking of Pete Lawrence's (@PortalPete) proposal
for better expression evaluator error messages:
#80938

Before:

```
$ lldb -o "expr a+b"
(lldb) expr a+b
error: <user expression 0>:1:1: use of undeclared identifier 'a'
a+b
^
error: <user expression 0>:1:3: use of undeclared identifier 'b'
a+b
  ^
```

After:

```
(lldb) expr a+b
            ^ ^
            │ ╰─ error: use of undeclared identifier 'b'
            ╰─ error: use of undeclared identifier 'a'
```

This eliminates the confusing `<user expression 0>:1:3` source
location and avoids echoing the expression to the console again, which
results in a cleaner presentation that makes it easier to grasp what's
going on. You can't see it here, bug the word "error" is now also in
color, if so desired.

Depends on #106442.

Author: adrian-prantl

lldb/include/lldb/API/SBDebugger.h

@@ -304,6 +304,8 @@ class LLDB_API SBDebugger {
 
   bool GetUseColor() const;
 
+  bool SetShowInlineDiagnostics(bool);
+
   bool SetUseSourceCache(bool use_source_cache);
 
   bool GetUseSourceCache() const;

lldb/include/lldb/Core/Debugger.h

@@ -364,6 +364,10 @@ class Debugger : public std::enable_shared_from_this<Debugger>,
 
   const std::string &GetInstanceName() { return m_instance_name; }
 
+  bool GetShowInlineDiagnostics() const;
+
+  bool SetShowInlineDiagnostics(bool);
+
   bool LoadPlugin(const FileSpec &spec, Status &error);
 
   void RunIOHandlers();

lldb/include/lldb/Expression/DiagnosticManager.h

@@ -39,6 +39,7 @@ struct DiagnosticDetail {
     unsigned line = 0;
     uint16_t column = 0;
     uint16_t length = 0;
+    bool hidden = false;
     bool in_user_input = false;
   };
   /// Contains {{}, 1, 3, 3, true} in the example above.

lldb/include/lldb/Interpreter/CommandObject.h

@@ -340,6 +340,13 @@ class CommandObject : public std::enable_shared_from_this<CommandObject> {
       return false;
   }
 
+  /// Set the command input as it appeared in the terminal. This
+  /// is used to have errors refer directly to the original command.
+  void SetOriginalCommandString(std::string s) { m_original_command = s; }
+
+  /// \param offset_in_command is on what column \c args_string
+  /// appears, if applicable. This enables diagnostics that refer back
+  /// to the user input.
   virtual void Execute(const char *args_string,
                        CommandReturnObject &result) = 0;
 
@@ -404,6 +411,7 @@ class CommandObject : public std::enable_shared_from_this<CommandObject> {
   std::string m_cmd_help_short;
   std::string m_cmd_help_long;
   std::string m_cmd_syntax;
+  std::string m_original_command;
   Flags m_flags;
   std::vector<CommandArgumentEntry> m_arguments;
   lldb::CommandOverrideCallback m_deprecated_command_override_callback;

lldb/source/API/SBDebugger.cpp

@@ -1483,6 +1483,12 @@ bool SBDebugger::GetUseColor() const {
   return (m_opaque_sp ? m_opaque_sp->GetUseColor() : false);
 }
 
+bool SBDebugger::SetShowInlineDiagnostics(bool value) {
+  LLDB_INSTRUMENT_VA(this, value);
+
+  return (m_opaque_sp ? m_opaque_sp->SetShowInlineDiagnostics(value) : false);
+}
+
 bool SBDebugger::SetUseSourceCache(bool value) {
   LLDB_INSTRUMENT_VA(this, value);
 

lldb/source/Commands/CommandObjectExpression.cpp

@@ -10,6 +10,7 @@
 
 #include "CommandObjectExpression.h"
 #include "lldb/Core/Debugger.h"
+#include "lldb/Expression/DiagnosticManager.h"
 #include "lldb/Expression/ExpressionVariable.h"
 #include "lldb/Expression/REPL.h"
 #include "lldb/Expression/UserExpression.h"
@@ -398,6 +399,122 @@ CanBeUsedForElementCountPrinting(ValueObject &valobj) {
   return Status();
 }
 
+static llvm::raw_ostream &PrintSeverity(Stream &stream,
+                                        lldb::Severity severity) {
+  llvm::HighlightColor color;
+  llvm::StringRef text;
+  switch (severity) {
+  case eSeverityError:
+    color = llvm::HighlightColor::Error;
+    text = "error: ";
+    break;
+  case eSeverityWarning:
+    color = llvm::HighlightColor::Warning;
+    text = "warning: ";
+    break;
+  case eSeverityInfo:
+    color = llvm::HighlightColor::Remark;
+    text = "note: ";
+    break;
+  }
+  return llvm::WithColor(stream.AsRawOstream(), color, llvm::ColorMode::Enable)
+         << text;
+}
+
+namespace lldb_private {
+// Public for unittesting.
+void RenderDiagnosticDetails(Stream &stream,
+                             std::optional<uint16_t> offset_in_command,
+                             bool show_inline,
+                             llvm::ArrayRef<DiagnosticDetail> details) {
+  if (details.empty())
+    return;
+
+  if (!offset_in_command) {
+    for (const DiagnosticDetail &detail : details) {
+      PrintSeverity(stream, detail.severity);
+      stream << detail.rendered << '\n';
+    }
+    return;
+  }
+
+  // Print a line with caret indicator(s) below the lldb prompt + command.
+  const size_t padding = *offset_in_command;
+  stream << std::string(padding, ' ');
+
+  size_t offset = 1;
+  std::vector<DiagnosticDetail> remaining_details, other_details,
+      hidden_details;
+  for (const DiagnosticDetail &detail : details) {
+    if (!show_inline || !detail.source_location) {
+      other_details.push_back(detail);
+      continue;
+    }
+    if (detail.source_location->hidden) {
+      hidden_details.push_back(detail);
+      continue;
+    }
+    if (!detail.source_location->in_user_input) {
+      other_details.push_back(detail);
+      continue;
+    }
+
+    auto &loc = *detail.source_location;
+    remaining_details.push_back(detail);
+    if (offset > loc.column)
+      continue;
+    stream << std::string(loc.column - offset, ' ') << '^';
+    if (loc.length > 1)
+      stream << std::string(loc.length - 1, '~');
+    offset = loc.column + 1;
+  }
+  stream << '\n';
+
+  // Work through each detail in reverse order using the vector/stack.
+  bool did_print = false;
+  for (auto detail = remaining_details.rbegin();
+       detail != remaining_details.rend();
+       ++detail, remaining_details.pop_back()) {
+    // Get the information to print this detail and remove it from the stack.
+    // Print all the lines for all the other messages first.
+    stream << std::string(padding, ' ');
+    size_t offset = 1;
+    for (auto &remaining_detail :
+         llvm::ArrayRef(remaining_details).drop_back(1)) {
+      uint16_t column = remaining_detail.source_location->column;
+      stream << std::string(column - offset, ' ') << "│";
+      offset = column + 1;
+    }
+
+    // Print the line connecting the ^ with the error message.
+    uint16_t column = detail->source_location->column;
+    if (offset <= column)
+      stream << std::string(column - offset, ' ') << "╰─ ";
+
+    // Print a colorized string based on the message's severity type.
+    PrintSeverity(stream, detail->severity);
+
+    // Finally, print the message and start a new line.
+    stream << detail->message << '\n';
+    did_print = true;
+  }
+
+  // Print the non-located details.
+  for (const DiagnosticDetail &detail : other_details) {
+    PrintSeverity(stream, detail.severity);
+    stream << detail.rendered << '\n';
+    did_print = true;
+  }
+
+  // Print the hidden details as a last resort.
+  if (!did_print)
+    for (const DiagnosticDetail &detail : hidden_details) {
+      PrintSeverity(stream, detail.severity);
+      stream << detail.rendered << '\n';
+    }
+}
+} // namespace lldb_private
+
 bool CommandObjectExpression::EvaluateExpression(llvm::StringRef expr,
                                                  Stream &output_stream,
                                                  Stream &error_stream,
@@ -486,19 +603,34 @@ bool CommandObjectExpression::EvaluateExpression(llvm::StringRef expr,
 
         result.SetStatus(eReturnStatusSuccessFinishResult);
       } else {
-        const char *error_cstr = result_valobj_sp->GetError().AsCString();
-        if (error_cstr && error_cstr[0]) {
-          const size_t error_cstr_len = strlen(error_cstr);
-          const bool ends_with_newline = error_cstr[error_cstr_len - 1] == '\n';
-          if (strstr(error_cstr, "error:") != error_cstr)
-            error_stream.PutCString("error: ");
-          error_stream.Write(error_cstr, error_cstr_len);
-          if (!ends_with_newline)
-            error_stream.EOL();
+        // Retrieve the diagnostics.
+        std::vector<DiagnosticDetail> details;
+        llvm::consumeError(llvm::handleErrors(
+            result_valobj_sp->GetError().ToError(),
+            [&](ExpressionError &error) { details = error.GetDetails(); }));
+        // Find the position of the expression in the command.
+        std::optional<uint16_t> expr_pos;
+        size_t nchar = m_original_command.find(expr);
+        if (nchar != std::string::npos)
+          expr_pos = nchar + GetDebugger().GetPrompt().size();
+
+        if (!details.empty()) {
+          bool show_inline =
+              GetDebugger().GetShowInlineDiagnostics() && !expr.contains('\n');
+          RenderDiagnosticDetails(error_stream, expr_pos, show_inline, details);
         } else {
-          error_stream.PutCString("error: unknown error\n");
+          const char *error_cstr = result_valobj_sp->GetError().AsCString();
+          llvm::StringRef error(error_cstr);
+          if (!error.empty()) {
+            if (!error.starts_with("error:"))
+              error_stream << "error: ";
+            error_stream << error;
+            if (!error.ends_with('\n'))
+              error_stream.EOL();
+          } else {
+            error_stream << "error: unknown error\n";
+          }
         }
-
         result.SetStatus(eReturnStatusFailed);
       }
     }

lldb/source/Core/CoreProperties.td

@@ -225,4 +225,8 @@ let Definition = "debugger" in {
     DefaultEnumValue<"eDWIMPrintVerbosityNone">,
     EnumValues<"OptionEnumValues(g_dwim_print_verbosities)">,
     Desc<"The verbosity level used by dwim-print.">;
+  def ShowInlineDiagnostics: Property<"show-inline-diagnostics", "Boolean">,
+    Global,
+    DefaultFalse,
+    Desc<"Controls whether diagnostics can refer directly to the command input, drawing arrows to it. If false, diagnostics will echo the input.">;
 }

lldb/source/Core/Debugger.cpp

@@ -592,7 +592,18 @@ lldb::DWIMPrintVerbosity Debugger::GetDWIMPrintVerbosity() const {
   const uint32_t idx = ePropertyDWIMPrintVerbosity;
   return GetPropertyAtIndexAs<lldb::DWIMPrintVerbosity>(
       idx, static_cast<lldb::DWIMPrintVerbosity>(
-               g_debugger_properties[idx].default_uint_value));
+               g_debugger_properties[idx].default_uint_value != 0));
+}
+
+bool Debugger::GetShowInlineDiagnostics() const {
+  const uint32_t idx = ePropertyShowInlineDiagnostics;
+  return GetPropertyAtIndexAs<bool>(
+      idx, g_debugger_properties[idx].default_uint_value);
+}
+
+bool Debugger::SetShowInlineDiagnostics(bool b) {
+  const uint32_t idx = ePropertyShowInlineDiagnostics;
+  return SetPropertyAtIndex(idx, b);
 }
 
 #pragma mark Debugger

lldb/source/Expression/DiagnosticManager.cpp

@@ -37,7 +37,7 @@ ExpressionError::ExpressionError(lldb::ExpressionResults result,
     : ErrorInfo(std::error_code(result, expression_category())), m_message(msg),
       m_details(details) {}
 
-static const char *StringForSeverity(lldb::Severity severity) {
+static llvm::StringRef StringForSeverity(lldb::Severity severity) {
   switch (severity) {
   // this should be exhaustive
   case lldb::eSeverityError:

lldb/source/Interpreter/CommandInterpreter.cpp

@@ -1887,7 +1887,8 @@ bool CommandInterpreter::HandleCommand(const char *command_line,
                                        CommandReturnObject &result,
                                        bool force_repeat_command) {
   std::string command_string(command_line);
-  std::string original_command_string(command_line);
+  std::string original_command_string(command_string);
+  std::string real_original_command_string(command_string);
 
   Log *log = GetLog(LLDBLog::Commands);
   llvm::PrettyStackTraceFormat stack_trace("HandleCommand(command = \"%s\")",
@@ -2076,6 +2077,7 @@ bool CommandInterpreter::HandleCommand(const char *command_line,
     }
 
     ElapsedTime elapsed(execute_time);
+    cmd_obj->SetOriginalCommandString(real_original_command_string);
     cmd_obj->Execute(remainder.c_str(), result);
   }