feat(debug): add debug flag and docs for dumping vet rule variables

docs/reference/environment-variables.md

@@ -126,6 +126,13 @@ return an error.
 
 `SQLCDEBUG=processplugins=0`
 
+### dumpvetenv
+
+The `dumpvetenv` command prints the variables available to a `sqlc vet` rule
+during evaluation.
+
+`SQLCDEBUG=dumpvetenv=1`
+
 ### dumpexplain
 
 The `dumpexplain` command prints the JSON-formatted result from running

internal/cmd/vet.go

@@ -430,6 +430,10 @@ func (c *checker) checkSQL(ctx context.Context, s config.SQL) error {
 				evalMap["mysql"] = engineOutput.MySQL
 			}
 
+			if debug.Debug.DumpVetEnv {
+				fmt.Printf("vars for rule '%s' evaluating against query '%s':\n%v\n", name, query.Name, evalMap)
+			}
+
 			out, _, err := (*rule.Program).Eval(evalMap)
 			if err != nil {
 				return err

internal/opts/debug.go

@@ -12,6 +12,8 @@ import (
 //     dumpcatalog: setting dumpcatalog=1 will print the parsed database schema
 //     trace: setting trace=<path> will output a trace
 //     processplugins: setting processplugins=0 will disable process-based plugins
+//     dumpvetenv: setting dumpvetenv=1 will print the variables available to
+//         a vet rule during evaluation
 //     dumpexplain: setting dumpexplain=1 will print the JSON-formatted output
 //         from executing EXPLAIN ... on a query during vet rule evaluation
 
@@ -20,6 +22,7 @@ type Debug struct {
 	DumpCatalog    bool
 	Trace          string
 	ProcessPlugins bool
+	DumpVetEnv     bool
 	DumpExplain    bool
 }
 
@@ -50,6 +53,8 @@ func DebugFromString(val string) Debug {
 			}
 		case pair == "processplugins=0":
 			d.ProcessPlugins = false
+		case pair == "dumpvetenv=1":
+			d.DumpVetEnv = true
 		case pair == "dumpexplain=1":
 			d.DumpExplain = true
 		}