Fix signature help crash for type arguments when call target is unresolved (#2295)

Author: DanielRosenwasser

…urslash/tests/signatureHelpCrash_test.go …natureHelpBetweenTypeArgsAndArgs_test.gointernal/fourslash/tests/signatureHelpCrash_test.go renamed to internal/fourslash/tests/signatureHelpBetweenTypeArgsAndArgs_test.go internal/fourslash/tests/signatureHelpCrash_test.go renamed to internal/fourslash/tests/signatureHelpBetweenTypeArgsAndArgs_test.go

@@ -0,0 +1,22 @@
+package fourslash_test
+
+import (
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/fourslash"
+	"github.com/microsoft/typescript-go/internal/testutil"
+)
+
+func TestSignatureHelpOnTypeArgumentsWithUnresolvedTarget(t *testing.T) {
+	t.Parallel()
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+	const content = `
+/*1*/un/*2*/resolvedVal/*3*/</*4*/Un/*5*/resolvedType/*6*/>/*7*/(/*8*/un/*9*/resolvedVal/*10*/);
+`
+	f, done := fourslash.NewFourslash(t, nil /*capabilities*/, content)
+	defer done()
+
+	f.GoToEachMarker(t, nil, func(marker *fourslash.Marker, index int) {
+		f.VerifyNoSignatureHelp(t)
+	})
+}

internal/fourslash/tests/signatureHelpTypeArgumentsWithUntypedTarget_test.go

@@ -670,10 +670,12 @@ func getCandidateOrTypeInfo(info *argumentListInfo, c *checker.Checker, sourceFi
 		if onlyUseSyntacticOwners && !isSyntacticOwner(startingToken, info.invocation.callInvocation.node, sourceFile) {
 			return nil
 		}
+
 		resolvedSignature, candidates := checker.GetResolvedSignatureForSignatureHelp(info.invocation.callInvocation.node, info.argumentCount, c)
 		if len(candidates) == 0 {
 			return nil
 		}
+
 		return &CandidateOrTypeInfo{
 			candidateInfo: &candidateInfo{
 				candidates:        candidates,
@@ -687,9 +689,11 @@ func getCandidateOrTypeInfo(info *argumentListInfo, c *checker.Checker, sourceFi
 		if ast.IsIdentifier(called) {
 			container = called.Parent
 		}
+
 		if onlyUseSyntacticOwners && !containsPrecedingToken(startingToken, sourceFile, container) {
 			return nil
 		}
+
 		candidates := getPossibleGenericSignatures(called, info.argumentCount, c)
 		if len(candidates) != 0 {
 			return &CandidateOrTypeInfo{
@@ -699,11 +703,17 @@ func getCandidateOrTypeInfo(info *argumentListInfo, c *checker.Checker, sourceFi
 				},
 			}
 		}
-		symbol := c.GetSymbolAtLocation(called)
-		return &CandidateOrTypeInfo{
-			typeInfo: symbol,
+
+		if symbol := c.GetSymbolAtLocation(called); symbol != nil {
+			return &CandidateOrTypeInfo{
+				typeInfo: symbol,
+			}
 		}
+
+		// This can happen in the case of an unresolved symbol.
+		return nil
 	}
+
 	if info.invocation.contextualInvocation != nil {
 		return &CandidateOrTypeInfo{
 			candidateInfo: &candidateInfo{