gopls/internal: don't show a warning if the Go version is undetected

CL 445581 inadvertently removed suppression of the Go version error if
the Go version was undetected. Add it back, with a test.

Fixes golang/go#56465

Change-Id: I352369096280c8d3423a7345123ec9309359fb58
Reviewed-on: https://go-review.googlesource.com/c/tools/+/446175
gopls-CI: kokoro <[email protected]>
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Robert Findley <[email protected]>

Author: findleyr

gopls/internal/lsp/general.go

@@ -251,13 +251,21 @@ func OldestSupportedGoVersion() int {
 	return GoVersionTable[len(GoVersionTable)-1].GoVersion + 1
 }
 
-func versionMessage(oldestVersion int) (string, protocol.MessageType) {
+// versionMessage returns the warning/error message to display if the user is
+// on the given Go version, if any. The goVersion variable is the X in Go 1.X.
+//
+// If goVersion is invalid (< 0), it returns "", 0.
+func versionMessage(goVersion int) (string, protocol.MessageType) {
+	if goVersion < 0 {
+		return "", 0
+	}
+
 	for _, v := range GoVersionTable {
-		if oldestVersion <= v.GoVersion {
+		if goVersion <= v.GoVersion {
 			var msgBuilder strings.Builder
 
 			mType := protocol.Error
-			fmt.Fprintf(&msgBuilder, "Found Go version 1.%d", oldestVersion)
+			fmt.Fprintf(&msgBuilder, "Found Go version 1.%d", goVersion)
 			if v.DeprecatedVersion != "" {
 				// not deprecated yet, just a warning
 				fmt.Fprintf(&msgBuilder, ", which will be unsupported by gopls %s. ", v.DeprecatedVersion)

gopls/internal/lsp/general_test.go

@@ -13,31 +13,32 @@ import (
 
 func TestVersionMessage(t *testing.T) {
 	tests := []struct {
-		goVer        int
+		goVersion    int
 		wantContains []string // string fragments that we expect to see
 		wantType     protocol.MessageType
 	}{
+		{-1, nil, 0},
 		{12, []string{"1.12", "not supported", "upgrade to Go 1.16", "install gopls v0.7.5"}, protocol.Error},
 		{13, []string{"1.13", "will be unsupported by gopls v0.11.0", "upgrade to Go 1.16", "install gopls v0.9.5"}, protocol.Warning},
 		{15, []string{"1.15", "will be unsupported by gopls v0.11.0", "upgrade to Go 1.16", "install gopls v0.9.5"}, protocol.Warning},
 		{16, nil, 0},
 	}
 
 	for _, test := range tests {
-		gotMsg, gotType := versionMessage(test.goVer)
+		gotMsg, gotType := versionMessage(test.goVersion)
 
 		if len(test.wantContains) == 0 && gotMsg != "" {
-			t.Errorf("versionMessage(%d) = %q, want \"\"", test.goVer, gotMsg)
+			t.Errorf("versionMessage(%d) = %q, want \"\"", test.goVersion, gotMsg)
 		}
 
 		for _, want := range test.wantContains {
 			if !strings.Contains(gotMsg, want) {
-				t.Errorf("versionMessage(%d) = %q, want containing %q", test.goVer, gotMsg, want)
+				t.Errorf("versionMessage(%d) = %q, want containing %q", test.goVersion, gotMsg, want)
 			}
 		}
 
 		if gotType != test.wantType {
-			t.Errorf("versionMessage(%d) = returned message type %d, want %d", test.goVer, gotType, test.wantType)
+			t.Errorf("versionMessage(%d) = returned message type %d, want %d", test.goVersion, gotType, test.wantType)
 		}
 	}
 }