From 5ac7ba2c6d3405f1a59f4350c753ec990af8f6dc Mon Sep 17 00:00:00 2001
From: Theresa Foley <10618364+tangent-vector@users.noreply.github.com>
Date: Tue, 20 Sep 2022 12:37:33 -0700
Subject: Support partial inference of generic arguments (#2404)

A commonly requested feature is to be able to supply only some
of the arguments to a generic explicitly, while allowing the rest
to be inferred. A common example is a function that performs some
kind of conversion:

    To convert<To, From>( From fromValue ) { .... }

A user would like to be able to call this operation like:

    int i = convert<int>( 1.0f );

but the current Slang type checker requires all or none of the generic
arguments be supplied. Supplying all of the arguments is tedious:

    int i = convert<int, float>( 1.0f );

In this case, the `float` type argument is redundant and could be
inferred from context. However, if the user tries to omit the generic
argument list:

    int i = convert( 1.0f );

The current type-checker cannot infer the `int` type argument (even if
one might claim it *should* infer based on the desired result type).

This change adds support for the `convert<int>(...)` case, by allowing
a generic to be applied to a prefix of its explicit arguments, and then
inferring the remaining arguments from contextual information when that
"partially applied" generic is applied to value-level arguments.

Most of the changes are just plumbing: adding the notion of a partially
applied generic and then supporting them during overload resolution.

A single test case is included that covers the `convert`-style use case.
It is likely that more testing is needed to cover failure modes of this
feature.
---
 source/slang/slang-check-decl.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

(limited to 'source/slang/slang-check-decl.cpp')

diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index 660e28802..a7cd768b1 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -5229,7 +5229,7 @@ namespace Slang
             if (!TryUnifyTypes(constraints, extDecl->targetType.Ptr(), type))
                 return DeclRef<ExtensionDecl>();
 
-            auto constraintSubst = TrySolveConstraintSystem(&constraints, DeclRef<Decl>(extGenericDecl, nullptr).as<GenericDecl>());
+            auto constraintSubst = trySolveConstraintSystem(&constraints, DeclRef<Decl>(extGenericDecl, nullptr).as<GenericDecl>());
             if (!constraintSubst)
             {
                 return DeclRef<ExtensionDecl>();
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