Fix 22384 - Add support for default values in C-style bitfields

[MadhurKumar004]

This implements parsing, semantic analysis, and backend support for default initializers in bitfields.

• Modified 'declaration.d' & 'parse.d' to parse assignment expressions after bitfield width.
• Updated 'dsymbolsem.d' to validate initializers and check for overflows.
• Updated 'todt.d' to pack default values into the binary representation.
• Added regression tests.

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[ibuclaw]

@MadhurKumar004 thanks for picking this up! 👍

[MadhurKumar004]

@ibuclaw Made the changes as you suggested

[MadhurKumar004]

@ibuclaw review please.

[ibuclaw]

Can't comment on the backend part. Frontend looks ok, maybe just need more combinations of tests to ensure we don't start accepting invalid code.

If there's bitfield documentation on dlang.org, that requires updating too.

As this is a feature fix, would be best to include a changelog entry too.

Thanks!

[MadhurKumar004]

@ibuclaw Thanks for the advice on test combination. Because of that i was able to fix couple of edge cases that were giving ICE. Also added the changelog and currently working on the dlang.org documentation. Will send a pr for that after this get merged. Please check and review

[ibuclaw]

Please rebase against current origin/master.

Suggested change

	s = new AST.BitFieldDeclaration(width.loc, t, ident, width, _init);
	s = new AST.BitFieldDeclaration(loc, t, ident, width, _init);

[MadhurKumar004]

Fixed.

[MadhurKumar004]

Can you please expand on what you mean by Location is still wrong?

[ibuclaw]

Front-end part LGTM. 👍

[ibuclaw]

Mind there are testsuite failures.

==============================
Test 'fail_compilation\biterrors.d' failed: 
diff:
----
-fail_compilation\biterrors.d(103): Error: initializer not allowed for bitfield declaration
 fail_compilation\biterrors.d(104): Error: storage class not allowed for bitfield declaration
----

==============================
Test 'fail_compilation\biterrors2.d' failed: 
diff:
----
 fail_compilation\biterrors2.d(100): Error: variable `biterrors2.a` - bitfield must be member of struct, union, or class
 int a : 2;
-    ^
+        ^
 fail_compilation\biterrors2.d(104): Error: bitfield `b` has zero width
     int b:0;
           ^
 fail_compilation\biterrors2.d(105): Error: bitfield type `float` is not an integer type
     float c:3;
-          ^
+            ^
----

==============================
Test 'fail_compilation\fail22384.d' failed: 
diff:
----
-fail_compilation\fail22384.d(21): Error: bitfield initializer `4294967295u` does not fit in 4 bits
-fail_compilation\fail22384.d(26): Error: bitfield initializer `E.B` does not fit in 2 bits
-fail_compilation\fail22384.d(30): Error: bitfield initializer `4` does not fit in 3 bits
-fail_compilation\fail22384.d(31): Error: bitfield initializer `65` does not fit in 7 bits
 fail_compilation\fail22384.d(32): Error: bitfield `z` has zero width
 fail_compilation\fail22384.d(36): Error: bitfield type `float` is not an integer type
 fail_compilation\fail22384.d(36): Error: bitfield `f` has zero width
 fail_compilation\fail22384.d(37): Error: bitfield type `float` is not an integer type
 fail_compilation\fail22384.d(38): Error: bitfield type `float` is not an integer type
 fail_compilation\fail22384.d(39): Error: bitfield type `float` is not an integer type
-fail_compilation\fail22384.d(43): Error: cannot implicitly convert expression `4.2F` of type `float` to `int`
 fail_compilation\fail22384.d(45): Error: anonymous bitfield cannot be initialized
+fail_compilation\fail22384.d(21): Error: bitfield initializer `4294967295u` does not fit in 4 bits
+fail_compilation\fail22384.d(26): Error: bitfield initializer `E.B` does not fit in 2 bits
+fail_compilation\fail22384.d(30): Error: bitfield initializer `4` does not fit in 3 bits
+fail_compilation\fail22384.d(31): Error: bitfield initializer `65` does not fit in 7 bits
+fail_compilation\fail22384.d(43): Error: cannot implicitly convert expression `4.2F` of type `float` to `int`
 fail_compilation\fail22384.d(46): Error: bitfield initializer `65` does not fit in 7 bits
 fail_compilation\fail22384.d(47): Error: cannot implicitly convert expression `42` of type `int` to `bool`
----

[MadhurKumar004]

@ibuclaw fixed the testsuite failure , whitespace and the correct error message. Also can you please explain what you mean by location is still wrong?