fix(11.1-07): require built, run src= code; case-sensitive go doc; parse command forms

- .go src= targets must be in the default build and reached from a Test or an Example with output
- go doc -c makes the identifier fallback case-sensitive
- commandWord parses env prefixes, flags, go run and bin/ forms

internal/docsite/check_identifiers.go

@@ -284,10 +284,10 @@ func isUpper(s string) bool {
 // optionally followed by one ".Member".
 var goDocIdent = regexp.MustCompile(`^[A-Za-z_][A-Za-z0-9_]*(\.[A-Za-z_][A-Za-z0-9_]*)?$`)
 
-// goDoc is the fallback for an index miss: `go doc ./<dir> <query>` run in
-// the repository root, so a declaration the index does not model still
-// counts. It runs without a shell, on an argument list whose query matches
-// goDocIdent.
+// goDoc is the fallback for an index miss: `go doc -c ./<dir> <query>`
+// run in the repository root, so a declaration the index does not model
+// still counts. -c makes the match case-sensitive. It runs without a
+// shell, on an argument list whose query matches goDocIdent.
 func (idx *identIndex) goDoc(dir, query string) bool {
 	if !goDocIdent.MatchString(query) {
 		return false
@@ -298,7 +298,7 @@ func (idx *identIndex) goDoc(dir, query string) bool {
 	}
 	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
 	defer cancel()
-	cmd := exec.CommandContext(ctx, "go", "doc", "./"+dir, query)
+	cmd := exec.CommandContext(ctx, "go", "doc", "-c", "./"+dir, query)
 	cmd.Dir = idx.root
 	cmd.Stdout, cmd.Stderr = nil, nil
 	ok := cmd.Run() == nil