Implement stderrPrint template function, suppress <nil> output (#224)

Implement stderrPrint template function, suppress <nil> output from stderrPrintf

gen/README.md

@@ -263,7 +263,8 @@ See https://pkg.go.dev/text/template#hdr-Functions
 | Template flow                                  | Description                    | webrpc-gen |
 |------------------------------------------------|-------------------------------------------------|-------------|
 | `minVersion {{.WebrpcVersion}} v1.4`           | Returns `boolean` if the given major/minor semver is at least v1.4 | v0.7.0 |
-| `stderrPrintf "format %v" ARGS...`             | `printf` to `webrpc-gen` stderr | v0.7.0 |
+| `stderrPrint ARGS...`                          | `print` to `webrpc-gen` CLI stderr | v0.13.0 |
+| `stderrPrintf "format %v" ARGS...`             | `printf` to `webrpc-gen` CLI stderr | v0.7.0 |
 | `exit INT`                                     | Terminate template execution, useful for fatal errors | v0.7.0 |
 | `dump VAR`                                     | Dump variable | v0.13.0 |
 | `hasField OBJ FIELD`                           | Check if object has a given field | v0.13.0 |

gen/funcmap.go

@@ -11,6 +11,7 @@ import (
 func templateFuncMap(opts map[string]interface{}) map[string]interface{} {
 	return map[string]interface{}{
 		// Template flow, errors, debugging.
+		"stderrPrint":  stderrPrint,  // v0.13.0
 		"stderrPrintf": stderrPrintf, // v0.7.0
 		"exit":         exit,         // v0.7.0
 		"minVersion":   minVersion,   // v0.7.0

gen/funcmap_flow.go

@@ -11,9 +11,17 @@ import (
 // Similar to "printf" but instead of writing into the generated
 // output file, stderrPrintf writes to webrpc-gen CLI stderr.
 // Useful for printing template errors / debugging.
-func stderrPrintf(format string, a ...interface{}) error {
-	_, err := fmt.Fprintf(os.Stderr, format, a...)
-	return err
+func stderrPrintf(format string, a ...interface{}) string {
+	_, _ = fmt.Fprintf(os.Stderr, format, a...)
+	return ""
+}
+
+// Similar to "print" but instead of writing into the generated
+// output file, stderrPrint writes to webrpc-gen CLI stderr.
+// Useful for printing template errors / debugging.
+func stderrPrint(a ...interface{}) string {
+	_, _ = fmt.Fprint(os.Stderr, a...)
+	return ""
 }
 
 // Terminate template execution with a status code.