[release-branch.go1.21] go/types, types2: use correct parameter list when checking argument passing

The existing code was simply wrong: we cannot ever use the result
signature parameter list (rsig.params) if sigParams was adjusted
for variadic functions. If it was adjusted, we always must either
use sigParams or its separately instantiated version.

In the condition "n > 0 && adjusted", the "n > 0" should have
been in either of the respective "if statement" branches.

Simplified the code by merging with the result signature parameter
update.

Fixes #61932.

Change-Id: I5d39bc8bbc4dd85c7c985055d29532b4b176955e
Reviewed-on: https://go-review.googlesource.com/c/go/+/519456
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/519417
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>

4 files changed, 60 insertions, 24 deletions

diff --git a/src/cmd/compile/internal/types2/call.go b/src/cmd/compile/internal/types2/call.go
index af27339967..f7a8a8dfcd 100644
--- a/src/cmd/compile/internal/types2/call.go
+++ b/src/cmd/compile/internal/types2/call.go
@@ -610,20 +610,17 @@ func (check *Checker) arguments(call *syntax.CallExpr, sig *Signature, targs []T
 			return // error already reported
 		}
 
-		// compute result signature: instantiate if needed
-		rsig = sig
+		// update result signature: instantiate if needed
 		if n > 0 {
 			rsig = check.instantiateSignature(call.Pos(), call.Fun, sig, targs[:n], xlist)
-		}
-
-		// Optimization: Only if the callee's parameter list was adjusted do we need to
-		// compute it from the adjusted list; otherwise we can simply use the result
-		// signature's parameter list. We only need the n type parameters and arguments
-		// of the callee.
-		if n > 0 && adjusted {
-			sigParams = check.subst(call.Pos(), sigParams, makeSubstMap(tparams[:n], targs[:n]), nil, check.context()).(*Tuple)
-		} else {
-			sigParams = rsig.params
+			// If the callee's parameter list was adjusted we need to update (instantiate)
+			// it separately. Otherwise we can simply use the result signature's parameter
+			// list.
+			if adjusted {
+				sigParams = check.subst(call.Pos(), sigParams, makeSubstMap(tparams[:n], targs[:n]), nil, check.context()).(*Tuple)
+			} else {
+				sigParams = rsig.params
+			}
 		}
 
 		// compute argument signatures: instantiate if needed
diff --git a/src/cmd/compile/internal/types2/issues_test.go b/src/cmd/compile/internal/types2/issues_test.go
index 5e0ae213dc..9f67ad0902 100644
--- a/src/cmd/compile/internal/types2/issues_test.go
+++ b/src/cmd/compile/internal/types2/issues_test.go
@@ -900,3 +900,23 @@ func _cgoCheckResult(interface{})
 		*boolFieldAddr(cfg, "go115UsesCgo") = true
 	})
 }
+
+func TestIssue61931(t *testing.T) {
+	const src = `
+package p
+
+func A(func(any), ...any) {}
+func B[T any](T)          {}
+
+func _() {
+	A(B, nil // syntax error: missing ',' before newline in argument list
+}
+`
+	f, err := syntax.Parse(syntax.NewFileBase(pkgName(src)), strings.NewReader(src), func(error) {}, nil, 0)
+	if err == nil {
+		t.Fatal("expected syntax error")
+	}
+
+	var conf Config
+	conf.Check(f.PkgName.Value, []*syntax.File{f}, nil) // must not panic
+}
diff --git a/src/go/types/call.go b/src/go/types/call.go
index 7258ab1237..8a3cec7309 100644
--- a/src/go/types/call.go
+++ b/src/go/types/call.go
@@ -612,20 +612,17 @@ func (check *Checker) arguments(call *ast.CallExpr, sig *Signature, targs []Type
 			return // error already reported
 		}
 
-		// compute result signature: instantiate if needed
-		rsig = sig
+		// update result signature: instantiate if needed
 		if n > 0 {
 			rsig = check.instantiateSignature(call.Pos(), call.Fun, sig, targs[:n], xlist)
-		}
-
-		// Optimization: Only if the callee's parameter list was adjusted do we need to
-		// compute it from the adjusted list; otherwise we can simply use the result
-		// signature's parameter list. We only need the n type parameters and arguments
-		// of the callee.
-		if n > 0 && adjusted {
-			sigParams = check.subst(call.Pos(), sigParams, makeSubstMap(tparams[:n], targs[:n]), nil, check.context()).(*Tuple)
-		} else {
-			sigParams = rsig.params
+			// If the callee's parameter list was adjusted we need to update (instantiate)
+			// it separately. Otherwise we can simply use the result signature's parameter
+			// list.
+			if adjusted {
+				sigParams = check.subst(call.Pos(), sigParams, makeSubstMap(tparams[:n], targs[:n]), nil, check.context()).(*Tuple)
+			} else {
+				sigParams = rsig.params
+			}
 		}
 
 		// compute argument signatures: instantiate if needed
diff --git a/src/go/types/issues_test.go b/src/go/types/issues_test.go
index 1a784aae21..64e1c20d7e 100644
--- a/src/go/types/issues_test.go
+++ b/src/go/types/issues_test.go
@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/importer"
+	"go/parser"
 	"go/token"
 	"internal/testenv"
 	"regexp"
@@ -908,3 +909,24 @@ func _cgoCheckResult(interface{})
 		*boolFieldAddr(cfg, "go115UsesCgo") = true
 	})
 }
+
+func TestIssue61931(t *testing.T) {
+	const src = `
+package p
+
+func A(func(any), ...any) {}
+func B[T any](T)          {}
+
+func _() {
+	A(B, nil // syntax error: missing ',' before newline in argument list
+}
+`
+	fset := token.NewFileSet()
+	f, err := parser.ParseFile(fset, pkgName(src), src, 0)
+	if err == nil {
+		t.Fatal("expected syntax error")
+	}
+
+	var conf Config
+	conf.Check(f.Name.Name, fset, []*ast.File{f}, nil) // must not panic
+}