From 855b1a262f3a769d44765e78f94e566d875b9286 Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Tue, 29 Jul 2025 07:35:58 -0700
Subject: [Language Server]: Show signature help on generic parameters. (#7913)

* Show signature help on generic parameters.

* Fix.

* Update tests.

* slang-test: make vvl error go through stderr.

* update slang-rhi

* Update slang-rhi
---
 source/slang/slang-language-server.cpp | 59 +++++++++++++++++++++++++++++++---
 1 file changed, 54 insertions(+), 5 deletions(-)

(limited to 'source/slang/slang-language-server.cpp')

diff --git a/source/slang/slang-language-server.cpp b/source/slang/slang-language-server.cpp
index 048fcb44b..dcf7419bd 100644
--- a/source/slang/slang-language-server.cpp
+++ b/source/slang/slang-language-server.cpp
@@ -160,6 +160,7 @@ SlangResult LanguageServer::parseNextMessage()
                     caps.semanticTokensProvider.full = true;
                     caps.semanticTokensProvider.range = false;
                     caps.signatureHelpProvider.triggerCharacters.add("(");
+                    caps.signatureHelpProvider.triggerCharacters.add("<");
                     caps.signatureHelpProvider.triggerCharacters.add(",");
                     caps.signatureHelpProvider.retriggerCharacters.add(",");
                     for (auto tokenType : kSemanticTokenTypes)
@@ -1705,14 +1706,33 @@ LanguageServerResult<LanguageServerProtocol::SignatureHelp> LanguageServerCore::
         bool useOriginalExpr = true;
         if (auto originalDeclRefExpr = as<DeclRefExpr>(appExpr->originalFunctionExpr))
         {
+            // If the original expr doesn't map to a valid declref, we will use the checked
+            // func expr instead.
             if (!originalDeclRefExpr->declRef)
             {
                 useOriginalExpr = false;
             }
         }
+        if (as<GenericAppExpr>(appExpr->originalFunctionExpr))
+        {
+            if (as<DeclRefExpr>(funcExpr))
+            {
+                // If the original function is a fully specialized generic app, use the checked func
+                // expr for signature help.
+                useOriginalExpr = false;
+            }
+        }
         if (useOriginalExpr)
             funcExpr = appExpr->originalFunctionExpr;
     }
+    if (auto partialGenAppExpr = as<PartiallyAppliedGenericExpr>(funcExpr))
+    {
+        funcExpr = partialGenAppExpr->originalExpr;
+    }
+    if (auto genAppExpr = as<GenericAppExpr>(funcExpr))
+    {
+        funcExpr = genAppExpr->functionExpr;
+    }
     if (!funcExpr)
     {
         return std::nullopt;
@@ -1741,6 +1761,22 @@ LanguageServerResult<LanguageServerProtocol::SignatureHelp> LanguageServerCore::
         if (!declRef.getDecl())
             return;
 
+        // If funcExpr is a direct reference to a generic, we should either
+        // show the generic signature if we are inside `<>`, or show the function
+        // parameter signature if we are inside `()`. If we are inside `()`, we will
+        // need to form a decl ref to the inner decl and show its signature.
+        if (!as<GenericAppExpr>(appExpr))
+        {
+            if (auto genDeclRef = as<GenericDecl>(declRef))
+            {
+                declRef = createDefaultSubstitutionsIfNeeded(
+                    version->linkage->getASTBuilder(),
+                    &semanticsVisitor,
+                    version->linkage->getASTBuilder()->getMemberDeclRef(
+                        declRef,
+                        genDeclRef.getDecl()->inner));
+            }
+        }
         // If we have a better match than the current best, we will update response.activeSignature
         // to this signature.
         if (auto callableDeclRef = declRef.as<CallableDecl>())
@@ -1832,12 +1868,20 @@ LanguageServerResult<LanguageServerProtocol::SignatureHelp> LanguageServerCore::
     {
         if (auto typeType = as<TypeType>(declRefExpr->type.type))
         {
-            // Look for initializers
-            auto ctors =
-                semanticsVisitor.lookupConstructorsInType(typeType->getType(), declRefExpr->scope);
-            for (auto ctor : ctors)
+            if (as<GenericDeclRefType>(typeType->getType()))
             {
-                addDeclRef(ctor.declRef);
+                addDeclRef(declRefExpr->declRef);
+            }
+            else
+            {
+                // Look for initializers
+                auto ctors = semanticsVisitor.lookupConstructorsInType(
+                    typeType->getType(),
+                    declRefExpr->scope);
+                for (auto ctor : ctors)
+                {
+                    addDeclRef(ctor.declRef);
+                }
             }
         }
         else
@@ -1847,8 +1891,13 @@ LanguageServerResult<LanguageServerProtocol::SignatureHelp> LanguageServerCore::
     }
     else if (auto overloadedExpr = as<OverloadedExpr>(funcExpr))
     {
+        bool isGenApp = as<GenericAppExpr>(appExpr) != nullptr;
         for (auto item : overloadedExpr->lookupResult2)
         {
+            // Skip non-generic candidates if we are inside a generic app expr (e.g.
+            // `f<WE_ARE_HERE>`).
+            if (isGenApp && !as<GenericDecl>(item.declRef))
+                continue;
             addDeclRef(item.declRef);
         }
     }
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