Work towards target-specific function overloads (#210)

* Checkpoint: interface conformance work

- Add explicit definition of `saturate` for the GLSL target, which calls through to `clamp`

- Needed to add explicit initializer to `__BuiltinFloatingPointType` to allow initialization from a single `float`, so that the `saturate` implementation can be sure that it can initialize a `T` from `0.0` or `1.0`.

- This triggered errors in overload resolution, because the logic in place could not figure out that the `T` of the outer generic (`saturate<T>()`) conformed to the interface required by the callee.

At this point I have the call to the scalar `clamp()` getting past type-checking, but not the vector or matrix cases.

* More fixups for overload resolution inside generics

- Make sure value parameters are treated the same as type parameters: we only want to solve for the parameters of the generic actually being applied, and not accidentally generate constraints for outer generics (e.g., when checking the body of a generic function).

- Make sure that the diagnostics stuff uses the correct source manager when expanding the location of a builtin.

* Fixes for function redeclaration

- Handle case of redeclaring a generic function
  - Enumerate siblings in the parent of the *generic* not the parent of the *function*
  - Add logic to compare generic signatures
  - When generic signatures match, specialize functions to compatible generic arguments before comparing the function signatures

- Fix redeclaration logic to *not* detect prefix/postifx operators as redeclarations of one another

- Build an explicit representation of function redeclaration groups
  - First declaration is the "primary" and others are stored in a linked list

- Make overload resolution handle redeclared functions
  - Only consider the primary declaration and skip others

1 files changed, 8 insertions, 2 deletions

diff --git a/source/slang/core.meta.slang b/source/slang/core.meta.slang
index 3f1a33edc..b792a74a3 100644
--- a/source/slang/core.meta.slang
+++ b/source/slang/core.meta.slang
@@ -10,13 +10,19 @@ interface __BuiltinArithmeticType : __BuiltinType {}
 interface __BuiltinSignedArithmeticType : __BuiltinArithmeticType {}
 
 // A type that can represent integers
-interface __BuiltinIntegerType : __BuiltinArithmeticType {}
+interface __BuiltinIntegerType : __BuiltinArithmeticType
+{}
 
 // A type that can represent non-integers
 interface __BuiltinRealType : __BuiltinArithmeticType {}
 
 // A type that uses a floating-point representation
-interface __BuiltinFloatingPointType : __BuiltinRealType, __BuiltinSignedArithmeticType {}
+interface __BuiltinFloatingPointType : __BuiltinRealType, __BuiltinSignedArithmeticType
+{
+    // A builtin floating-point type must have an initializer that takes
+    // a floating-point value...
+    __init(float value);
+}
 
 __generic<T,U> __intrinsic_op(Sequence) U operator,(T left, U right);