Create serializable synthetic call-signature declarations

Co-authored-by: weswigham <2932786+weswigham@users.noreply.github.com>

packages/typescript/test/async/api.test.ts

@@ -4967,7 +4967,17 @@ describe("Checker - getContextualType", { concurrency }, () => {
         const signatures = await project.checker.getSignaturesOfType(type, SignatureKind.Call);
         assert.equal(signatures.length, 1);
         assert.deepEqual((await signatures[0].getParameters()).map(parameter => parameter.name), ["target", "context"]);
-        assert.equal(signatures[0].declaration, undefined);
+        const declarationHandle = signatures[0].declaration;
+        assert.ok(declarationHandle);
+        assert.equal(declarationHandle.kind, SyntaxKind.FunctionType);
+        const declaration = await declarationHandle.resolve();
+        assert.ok(declaration);
+        assert.ok(isSignatureDeclaration(declaration));
+        assert.equal(declaration.kind, SyntaxKind.FunctionType);
+        const declarationSignature = await project.checker.getSignatureFromDeclaration(declaration);
+        assert.ok(declarationSignature);
+        assert.strictEqual(declarationSignature.declaration, declarationHandle);
+        assert.deepEqual(await project.program.getSourceFileNames(), ["/src/main.ts"]);
     });
 
     test("contextual type from function parameter", async () => {

packages/typescript/test/sync/api.test.ts

@@ -4792,7 +4792,17 @@ describe("Checker - getContextualType", { concurrency }, () => {
         const signatures = project.checker.getSignaturesOfType(type, SignatureKind.Call);
         assert.equal(signatures.length, 1);
         assert.deepEqual((signatures[0].getParameters()).map(parameter => parameter.name), ["target", "context"]);
-        assert.equal(signatures[0].declaration, undefined);
+        const declarationHandle = signatures[0].declaration;
+        assert.ok(declarationHandle);
+        assert.equal(declarationHandle.kind, SyntaxKind.FunctionType);
+        const declaration = declarationHandle.resolve();
+        assert.ok(declaration);
+        assert.ok(isSignatureDeclaration(declaration));
+        assert.equal(declaration.kind, SyntaxKind.FunctionType);
+        const declarationSignature = project.checker.getSignatureFromDeclaration(declaration);
+        assert.ok(declarationSignature);
+        assert.strictEqual(declarationSignature.declaration, declarationHandle);
+        assert.deepEqual(project.program.getSourceFileNames(), ["/src/main.ts"]);
     });
 
     test("contextual type from function parameter", () => {

tsc/internal/api/session.go

@@ -501,8 +501,8 @@ func (sd *snapshotData) newSignatureResponse(projectID project.Handle, sig *chec
 		Flags: uint32(sig.Flags()),
 	}
 
-	if declaration := sig.Declaration(); declaration != nil && ast.GetSourceFileOfNode(declaration) != nil {
-		resp.Declaration = sd.nodeHandleFrom(declaration)
+	if sig.Declaration() != nil {
+		resp.Declaration = sd.nodeHandleFrom(sig.Declaration())
 	}
 
 	if len(sig.TypeParameters()) > 0 {
@@ -2362,7 +2362,11 @@ func (s *Session) handleGetSourceFile(ctx context.Context, params *GetSourceFile
 		return nil, err
 	}
 
-	return s.encodeSourceFileResponse(program.GetSourceFile(params.File.ToFileName(program.BaseDirectory())))
+	fileName := params.File.ToFileName(program.BaseDirectory())
+	if fileName == checker.SyntheticSignatureFileName {
+		return s.encodeSourceFileResponse(checker.GetSyntheticSignatureSourceFile())
+	}
+	return s.encodeSourceFileResponse(program.GetSourceFile(fileName))
 }
 
 // handleGetConfigFileNames returns tsconfig file names associated with the project's command line.
@@ -5029,6 +5033,12 @@ func (sd *snapshotData) resolveNodeHandle(program *compiler.Program, handle Node
 		return nil, fmt.Errorf("%w: invalid node handle %q", ErrClientError, handle)
 	}
 	sourceFile := program.GetSourceFileByNodeID(ast.NodeId(nodeID))
+	if sourceFile == nil {
+		syntheticFile := checker.GetSyntheticSignatureSourceFile()
+		if sourceFileNodeID(syntheticFile) == nodeID {
+			sourceFile = syntheticFile
+		}
+	}
 	if sourceFile == nil {
 		return nil, fmt.Errorf("%w: node handle %q could not be resolved (file may not be loaded or handle may be stale)", ErrClientError, handle)
 	}

tsc/internal/checker/checker.go

@@ -31161,7 +31161,7 @@ func (c *Checker) newSetterFunctionType(t *Type) *Type {
 
 // Creates a synthetic `Signature` corresponding to a call signature.
 func (c *Checker) newCallSignature(typeParameters []*Type, thisParameter *ast.Symbol, parameters []*ast.Symbol, returnType *Type) *Signature {
-	decl := c.factory.NewFunctionTypeNode(nil, nil, c.factory.NewKeywordTypeNode(ast.KindAnyKeyword))
+	decl := GetSyntheticSignatureSourceFile().Statements.Nodes[0].Type()
 	return c.newSignature(SignatureFlagsNone, decl, typeParameters, thisParameter, parameters, returnType, nil, len(parameters))
 }
 

tsc/internal/checker/syntheticsignature.go

@@ -0,0 +1,25 @@
+package checker
+
+import (
+	"sync"
+
+	"github.com/microsoft/TypeScript/tsc/internal/ast"
+	"github.com/microsoft/TypeScript/tsc/internal/core"
+	"github.com/microsoft/TypeScript/tsc/internal/parser"
+	"github.com/microsoft/TypeScript/tsc/internal/tspath"
+)
+
+const SyntheticSignatureFileName tspath.RootedFilePath = "tsgo://synthetic/signatures.d.ts"
+
+var syntheticSignatureSourceFile = sync.OnceValue(func() *ast.SourceFile {
+	return parser.ParseSourceFile(ast.SourceFileParseOptions{
+		FileName: SyntheticSignatureFileName,
+		PathKey:  tspath.CaseSensitive.PathKey(tspath.RootedPath(SyntheticSignatureFileName)),
+	}, "type SyntheticSignature = () => any;", core.ScriptKindTS)
+})
+
+// GetSyntheticSignatureSourceFile provides an immutable, shared AST for synthetic
+// call-signature declarations. It is not an input file of any program.
+func GetSyntheticSignatureSourceFile() *ast.SourceFile {
+	return syntheticSignatureSourceFile()
+}