[dev.typeparams] cmd/compile/internal/types2: add support for language version checking

Add the Config.Lang field which may be set to a Go version string,
such as "go1.12". This is a string rather than explicit semantic
version numbers (such as {1, 12}) for API robustness; a string
is more flexible should we need more or different information.

Add -lang flag to types2 package for use with (manual) testing
when running "go test -run Check$ -lang=... -files=...".

While changing flags, look for comma-separated (rather than space-
separated) files when providing the -file flag.

Check that numeric constant literals, signed shift counts are
accepted according to the selected language version.

Type alias declarations and overlapping embedded interfaces are
not yet checked.

Updates #31793.

Change-Id: I9ff238ed38a88f377eb2267dc3e8816b89a40635
Reviewed-on: https://go-review.googlesource.com/c/go/+/289509
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/types2/api.go b/src/cmd/compile/internal/types2/api.go
index b29c0802ed..30f0430ff1 100644
--- a/src/cmd/compile/internal/types2/api.go
+++ b/src/cmd/compile/internal/types2/api.go
@@ -99,6 +99,13 @@ type ImporterFrom interface {
 // A Config specifies the configuration for type checking.
 // The zero value for Config is a ready-to-use default configuration.
 type Config struct {
+	// GoVersion describes the accepted Go language version. The string
+	// must follow the format "go%d.%d" (e.g. "go1.12") or ist must be
+	// empty; an empty string indicates the latest language version.
+	// If the format is invalid, invoking the type checker will cause a
+	// panic.
+	GoVersion string
+
 	// If IgnoreFuncBodies is set, function bodies are not
 	// type-checked.
 	IgnoreFuncBodies bool