CLion 2026.1's Constexpr Debugger Steps Into Compile-Time Evaluation

CLion 2026.1 ships a constexpr debugger – the first tool that lets you step through compile-time constant evaluations like you would a normal runtime call stack. Instead of deciphering cryptic compiler errors when a constexpr function fails, you can now run the evaluation until failure and stop exactly where things went wrong, with locals, call stack, and even backward stepping available.

Constexpr Debugger: Stepping Into Compile-Time

Introduced in CLion 2025.3 and now fully integrated in 2026.1 with the Nova engine, the Constexpr Debugger treats constant evaluation as just another execution path. You can set breakpoints inside constexpr and consteval functions, inspect variables, and step backward through each evaluation stage. For me, this closes a long-standing gap: compile-time programming no longer requires black-box debugging.

The IDE also detects evaluation failures early with a new inspection popup that shows an evaluation trace. Clicking "Run evaluation until failure" launches the debugger directly at the failing point — no more reading template error spew.

C++26 Features: #embed, Pack Indexing, Variadic Friends

CLion 2026.1 supports all C++26 features except reflection (slated for 2026.2, tracking issue CPP-48365). Three stand out:

• #embed: Embed binary files as byte arrays at compile time. constexpr unsigned char logo[] = { #embed "logo.png" }; — no more external scripts to convert images to C arrays.
• Pack indexing: Access parameter pack elements by index directly: args...[I]. No recursive templates needed.
• Variadic friends: Grant friendship to all types in a template parameter pack with friend Ts...;. Cleaner for data structure nodes that need mutual private access.

GCC and Clang Extensions: Nested Functions and Nullability

Four compiler extensions now work without false positives:

• Nested functions (GCC) — useful for legacy embedded codebases.
• _Nullable and _Nonnull qualifiers (Clang) — no more spurious warnings on Apple-platform code.
• Omitted-operand conditionals (x ?: y) — GNU C shorthand.
• Designated initializer range syntax ([0 ... 49] = 0) — handy for hardware register maps and lookup tables.

New Inspections and Refactoring for Modern Code

CLion now auto-imports C++20 module symbols when you use an exported name. It detects duplicate forward declarations, redundant typename keywords in C++20 or later, misordered designated initializers, and access-level mismatches in virtual function overrides. Inactive preprocessor blocks get full code analysis, completion, and refactorings — no need to switch build configurations to edit platform-specific code.

One practical addition: automatic sorting of function definitions in source files to match the declaration order in the header. Enable it as a style option, and CLion flags mismatches with a one-click fix.

With the constexpr debugger and C++26 support shipped, the next milestone is reflection in CLion 2026.2 – I'll be watching that YouTrack issue closely.

Source: Modern C++ Support in CLion: What's New
Domain: blog.jetbrains.com