Add Release Notes for v2.38.0 (#1581)

Author: serban-nicusor-toptal

RELEASE-NOTES.txt

@@ -1,6 +1,42 @@
 STANC3 RELEASE NOTES
 ======================================================================
 
+v2.38.0 (13 January 2026)
+======================================================================
+
+- Improved formatting and wording of compiler warnings and error messages. These
+    can display in color when the output is a supporting terminal. This can be
+    overriden with `--color=never` or `$STANC_COLORS` set to `never`.
+    (#1548, #1551, #1546, #1549, #1550, #1552, #1561, #1560)
+ - Expiring deprecation: `jacobian` is now a reserved keyword. (#1573)
+ - Added new functions: wiener_lcdf_defective and wiener_lccdf_defective for use with the wiener distribution. (#1576)
+ - Added new overloads to the 5/8 argument wiener_lpdf functions with an additional data real argument to control the precision of the gradient. (#1576)
+ - Command line flags like `--use-opencl` can be passed multiple times once more. This is equivalent to passing them exactly once, and is only provided for backwards compatibility with existing code that may not properly prepare the arguments to the compiler. (#1541)
+ - `--debug-mem-patterns` will now output information about why each variable was not considered a candidate for the SoA optimization. (#1566)
+ - Autocomplete scripts (for bash, zsh, and powershell) and manpages are now available for the stanc compiler. (#1572, #1558)
+ - Fixed a pedantic warning referring to a now-incorrect location in the user's guide. (#1567)
+ - All warnings from pedantic mode will now have a location associated with them. (#1568)
+ - The C++ generated by models with many individually named parameters should be less likely to produce errors complaining about `bracket depth exceeded`. (#1542)
+ - Improved code generation of user-defined functions accepting tuples to resolve some C++ compilation errors. (#1556)
+ - Fixed an issue where some function names like `min` could lead to conflicts with the C++ standard library if they were overloaded by a user. (#1557)
+ - Generated C++ now always encodes when we expect integers to become doubles. (#1577)
+ - Updated C++ templating around autodiff scalars. (#1555)
+ - Fixed the some of the newer constraint types not having sufficient size checks for their declarations in the generated C++. (#1563)
+ - Fixed a compiler crash that could be triggered by certain nested `#include` statements. (#1564)
+ - Improved the formatting of long functions (either with long names or many arguments). (#1562)
+ - stanc.js can request ANSI escape code styling in errors and warnings by passing `color-output` as an argument. These are supported in most browser consoles. (#1569)
+ - Removed unused code from Common. (#1538)
+ - Cleaned up pretty-printer code. (#1527)
+ - Reduced cross-module access to mutable state. (#1543)
+ - Encapsulated local exception usage. (#1544)
+ - Statically forbid promotion nodes in the untyped AST. (#1545)
+ - Fixed inconsistency in whether locations are opaque in sexps. (#1547)
+ - stanc3js will no longer try to load node modules at startup. (#1553)
+ - `dune build @install` no longer adds stanc's testing executables to the `bin` folder. (#1571)
+ - Cleaned up dune-project file. (#1574)
+ - Updated `ocamlformat` to 0.28 (#1570)
+ - Updated Fmt to 0.11.0 (#1537)
+
 v2.37.0 (2 September 2025)
 ======================================================================