[lldb] Support custom LLVM formatting for variables

lldb/docs/use/variable.rst

@@ -460,6 +460,15 @@ summary strings, regardless of the format they have applied to their types. To
 do that, you can use %format inside an expression path, as in ${var.x->x%u},
 which would display the value of x as an unsigned integer.
 
+Additionally, custom output can be achieved by using an LLVM format string,
+commencing with the ``:`` marker. To illustrate, compare ``${var.byte%x}`` and
+``${var.byte:x-}``. The former uses lldb's builtin hex formatting (``x``),
+which unconditionally inserts a ``0x`` prefix, and also zero pads the value to
+match the size of the type. The latter uses ``llvm::formatv`` formatting
+(``:x-``), and will print only the hex value, with no ``0x`` prefix, and no
+padding. This raw control is useful when composing multiple pieces into a
+larger whole.
+
 You can also use some other special format markers, not available for formats
 themselves, but which carry a special meaning when used in this context:
 

lldb/source/Core/FormatEntity.cpp

@@ -57,6 +57,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Compiler.h"
+#include "llvm/Support/Regex.h"
 #include "llvm/TargetParser/Triple.h"
 
 #include <cctype>
@@ -658,6 +659,38 @@ static char ConvertValueObjectStyleToChar(
   return '\0';
 }
 
+static llvm::Regex LLVMFormatPattern{"x[-+]?\\d*|n|d", llvm::Regex::IgnoreCase};
+
+static bool DumpValueWithLLVMFormat(Stream &s, llvm::StringRef options,
+                                    ValueObject &valobj) {
+  std::string formatted;
+  std::string llvm_format = ("{0:" + options + "}").str();
+
+  // Options supported by format_provider<T> for integral arithmetic types.
+  // See table in FormatProviders.h.
+
+  auto type_info = valobj.GetTypeInfo();
+  if (type_info & eTypeIsInteger && LLVMFormatPattern.match(options)) {
+    if (type_info & eTypeIsSigned) {
+      bool success = false;
+      int64_t integer = valobj.GetValueAsSigned(0, &success);
+      if (success)
+        formatted = llvm::formatv(llvm_format.data(), integer);
+    } else {
+      bool success = false;
+      uint64_t integer = valobj.GetValueAsUnsigned(0, &success);
+      if (success)
+        formatted = llvm::formatv(llvm_format.data(), integer);
+    }
+  }
+
+  if (formatted.empty())
+    return false;
+
+  s.Write(formatted.data(), formatted.size());
+  return true;
+}
+
 static bool DumpValue(Stream &s, const SymbolContext *sc,
                       const ExecutionContext *exe_ctx,
                       const FormatEntity::Entry &entry, ValueObject *valobj) {
@@ -728,9 +761,12 @@ static bool DumpValue(Stream &s, const SymbolContext *sc,
     return RunScriptFormatKeyword(s, sc, exe_ctx, valobj, entry.string.c_str());
   }
 
-  llvm::StringRef subpath(entry.string);
+  auto split = llvm::StringRef(entry.string).split(':');
+  auto subpath = split.first;
+  auto llvm_format = split.second;
+
   // simplest case ${var}, just print valobj's value
-  if (entry.string.empty()) {
+  if (subpath.empty()) {
     if (entry.printf_format.empty() && entry.fmt == eFormatDefault &&
         entry.number == ValueObject::eValueObjectRepresentationStyleValue)
       was_plain_var = true;
@@ -739,22 +775,19 @@ static bool DumpValue(Stream &s, const SymbolContext *sc,
     target = valobj;
   } else // this is ${var.something} or multiple .something nested
   {
-    if (entry.string[0] == '[')
+    if (subpath[0] == '[')
       was_var_indexed = true;
     ScanBracketedRange(subpath, close_bracket_index,
                        var_name_final_if_array_range, index_lower,
                        index_higher);
 
     Status error;
 
-    const std::string &expr_path = entry.string;
-
-    LLDB_LOGF(log, "[Debugger::FormatPrompt] symbol to expand: %s",
-              expr_path.c_str());
+    LLDB_LOG(log, "[Debugger::FormatPrompt] symbol to expand: {0}", subpath);
 
     target =
         valobj
-            ->GetValueForExpressionPath(expr_path.c_str(), &reason_to_stop,
+            ->GetValueForExpressionPath(subpath, &reason_to_stop,
                                         &final_value_type, options, &what_next)
             .get();
 
@@ -883,8 +916,18 @@ static bool DumpValue(Stream &s, const SymbolContext *sc,
   }
 
   if (!is_array_range) {
-    LLDB_LOGF(log,
-              "[Debugger::FormatPrompt] dumping ordinary printable output");
+    if (!llvm_format.empty()) {
+      if (DumpValueWithLLVMFormat(s, llvm_format, *target)) {
+        LLDB_LOGF(log, "dumping using llvm format");
+        return true;
+      } else {
+        LLDB_LOG(
+            log,
+            "empty output using llvm format '{0}' - with type info flags {1}",
+            entry.printf_format, target->GetTypeInfo());
+      }
+    }
+    LLDB_LOGF(log, "dumping ordinary printable output");
     return target->DumpPrintableRepresentation(s, val_obj_display,
                                                custom_format);
   } else {
@@ -2227,6 +2270,13 @@ static Status ParseInternal(llvm::StringRef &format, Entry &parent_entry,
           if (error.Fail())
             return error;
 
+          auto [_, llvm_format] = llvm::StringRef(entry.string).split(':');
+          if (!LLVMFormatPattern.match(llvm_format)) {
+            error.SetErrorStringWithFormat("invalid llvm format: '%s'",
+                                           llvm_format.data());
+            return error;
+          }
+
           if (verify_is_thread_id) {
             if (entry.type != Entry::Type::ThreadID &&
                 entry.type != Entry::Type::ThreadProtocolID) {

lldb/test/API/functionalities/data-formatter/custom-printf-summary/Makefile

@@ -0,0 +1,2 @@
+C_SOURCES := main.c
+include Makefile.rules

lldb/test/API/functionalities/data-formatter/custom-printf-summary/TestCustomSummaryLLVMFormat.py

@@ -0,0 +1,20 @@
+import lldb
+from lldbsuite.test.lldbtest import *
+import lldbsuite.test.lldbutil as lldbutil
+
+
+class TestCase(TestBase):
+    def test_raw_bytes(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "break here", lldb.SBFileSpec("main.c"))
+        self.runCmd("type summary add -s '${var.ubyte:x-2}${var.sbyte:x-2}!' Bytes")
+        self.expect("v bytes", substrs=[" = 3001!"])
+
+    def test_bad_format(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "break here", lldb.SBFileSpec("main.c"))
+        self.expect(
+            "type summary add -s '${var.ubyte:y}!' Bytes",
+            error=True,
+            substrs=["invalid llvm format"],
+        )

lldb/test/API/functionalities/data-formatter/custom-printf-summary/main.c

@@ -0,0 +1,13 @@
+#include <stdint.h>
+#include <stdio.h>
+
+struct Bytes {
+  uint8_t ubyte;
+  int8_t sbyte;
+};
+
+int main() {
+  struct Bytes bytes = {0x30, 0x01};
+  (void)bytes;
+  printf("break here\n");
+}