I also write Free Pascal using Lazarus, an IDE which actually understands the language at a deep level.
The experience writing the latter is way *WAY* better than the former and my opinion to that isn't "just write more in Free Pascal" but "i want an IDE for C that is at least as good as Lazarus is for Free Pascal".
I want a C IDE that, among others:
1. Can understand the code so that when i, e.g., want to rename the identifier "foo" it doesn't try to rename it as a keyword but knows if it refers to a local variable, global variable or struct member and only update references to that.
2. Can understand the code so that if i use a symbol defined in a header file that the current module doesn't include by itself it can put it in the includes section automatically (or at least ask me to) instead of waiting for the compiler to fail. If there is some conflict (e.g. because the symbol definition depends on macros or whatever) it should be able to understand that.
3. Can understand the code so that it can move structs, functions, etc around in modules and update header files and their uses in other modules automatically.
4. Can understand the code so that it can convert a struct defined in a header file to an opaque struct and vice versa, for the former being able to tell me which existing code would break and offer fixes (e.g. automatically creating accessor functions for the members).
5. Can understand the code so that it can expand macros in place visually, allow me to edit the macros expanded in-place while actually modifying the header file (or wherever the macro is defined) and also quickly tell me where the macro is used in other places.
6. Can understand the code so that it can convert code to functions, expand functions inline (with any local variables being placed at a decent position and any conflicts handled - it can ask for example if it sees the inline code to use "for (i=1; i<10;" and the existing code also has a "int i" if it should reuse the "int i" or replace it with heuristics that provide decent defaults), add/remove arguments (with automatic updates wherever they are used), etc.
7. Can understand the code so that one can create queries like "replace all string literals to non-static functions whose name matches the '^foo_.*$' regex with calls to macro 'TXT' and the same string literal as the parameter to macro".
8. Has a debugger that works with all the basics (breakpoints, step in/through/out, watches, etc) and...
9. The debugger can modify a variable while the program is running.
10. The debugger can make function calls while the program is running.
11. The debugger can modify a function while the program is running (any new calls are done to that function).
12. The debugger can watch data over time and be able to display values in various means like various graph types.
13. The debugger can tell you where (in code) some use-after-free was originally allocated and then where it was freed and where it was used, all with nicely shown arrows, hyperlinks and graphics directly inside the editor instead of you having to manually parse (in your head) some callstack. Similar for other types of errors like accessing invalid pointers, array data out of range (should tell you both the range and the accessed index where that can be statically inferred), etc.
14. The debugger can put conditional breakpoints which:
14a. Can call functions defined in the program.
14b. Can check if the breakpoint comes from a specific callstack (e.g. break if function "foo" is called from "bar" but not from "baz").
14c. Can access local variables and arguments up the callstack (obviously the breakpoint will only break where that is possible).
15. There is a profiler that works and...
16. The profiler can create call-based profiles (think gprof) and statistics-based profiles (think perf).
17. The profiler can record the full callstack instead of just the function name.
18. The profiler can create full call diagrams (see Luke Stackwalker[0] as an example) as well as flamegraphs (see some perl script for perf i don't remember).
19. The profiler can keep track not only where* but also when* a sample was taken so it can create profile timelines. Actually just have it do everything i had a profiler i wrote some time ago for Free Pascal[1], including be able to be instrumented by the running program, filter via thread, call stack depth, etc.
20. The profiler can call functions in the profiled program to create additional profile (e.g. if you want to count how many files are opened or how many rays your raytracer is casting or whatever so you can use the full profiler functionality instead of hacking up your own)
21. There is a static analysis tool that works and...
22. ...works like whatever Xcode's integration with Clang's analyzer is, i do not have much experience with those but i remember using it a couple of times years ago and thinking it was neat. I haven't seen any other graphical integration of a code analysis tool, pretty much every other analyzer feels like compiler warnings++. More of the graphical approach and less of the warnings++ approach please.
23. There is some form of project management / build tool / whatever that the IDE uses and...
24. The IDE can let you setup various "configurations" for build options (including preprocessor defines, which files/objects/libraries are to be included, etc) that can be mixed and matched at will (e.g. a "lightweight" and "full" configuration set could be mixed with a "win32" and "linux" configuration set with the latter relying on the "unix" configuration and none of those would need you to duplicate any information).
25. The IDE can know about libraries, be able to locate them as well as place them in appropriate locations when you are building a library. Libraries should be able to be built as both statically and dynamically linked if that is needed. If a library A relies on another library B and a program uses library A it should not need to also specify library B too - in the exceptional case where that is needed (e.g. there are alternative versions of library B) it should allow that but it should not be necessary.
26. Setting up the above should not need to be done via arcane text files but via a nice GUI that doesn't hate the user - e.g. using a library should not need you to type it's name but allow you to check next to its name in a listbox with checkboxes (with name filtering and categories). It should also know about different system libraries for the same thing (e.g. OpenGL in Windows, Linux and Mac is accessed via different ways). This should be configurable, not hardcoded - a custom library should also be able to use that functionality. Note that all of this can be stored in text files (e.g. for easier VCS support) but not needed.
27. More of a #26b but i think it deserves its own point: in addition the IDE should have deep knowledge of what a library offers and like #2 if it knows a symbol being offered by a library it should automatically add it to your project's requirements.
28. Again more of a #27b but also a #2b: it should be able to clean up any unused stuff (either automatic or explicitly). In total i should, e.g, be able to use OpenGL by typing "gl", pressing the auto-complete key (ctrl+space or whatever) and have the IDE suggest all the "gl" prefixed functions like "glClear", then once i select "glClear" (or whatever), the IDE adds the #include <GL/gl.h> header and the libgl library in the dependencies. If i press Ctrl-Z to undo that, the header files and library dependencies (if added) will be removed. If i press Ctrl+S to save or some other key to cleanup the project (depending on the configuration), any unused headers and libraries should be removed.
I could write for more but basically i'd like an IDE (i haven't touched topics like VCS support and how i'd like to be able to see and use different version of the code from inside the IDE - like e.g. go back in time to a different function while the debugger is running - or anything that has to do with GUIs) that is smart and helps me get rid of all the manual drudge,
(also FWIW little of the above is provided by Lazarus and i'd also like Lazarus to do all that where it makes sense but it still does more than pretty much any C IDE i've used)