config init now leaves out the test sources unless given --all

A section tagged init:"hidden" isn't written to the file config init
generates; fts_mock and sleeper are. config init --all writes them too.
They still load, and the config commands read and set them as before.

internal/config/README.md

@@ -267,6 +267,10 @@ per key:
   of the configuration.
 - `default:"value"` is the field's default, parsed as if it were a string
   passed to `SetValue` (e.g. `"10m"`, `"true"`).
+- `init:"hidden"` on a nested section's field leaves the section out of the
+  file `config init` writes, unless `--all` is given (`InitDefaults`). The
+  test sources, `fts_mock` and `sleeper`, have it. The section is otherwise
+  as any other: loaded, and read and set by the `config` commands.
 - A tagged field whose type is a struct is a nested section, addressed as
   `section.key`. An embedded struct has its fields promoted, as Go does;
   every source embeds `JSCSourcesSource` for `enabled` and `interval`.
@@ -324,7 +328,8 @@ To add a new section:
    `JSCRateLimitRule`, has no constant and passes `""` to `flattenOf`.
 2. Add the struct as a tagged field of its parent: `JobSearchConfig` in
    `config.go`, or `JSCSources` in `conf_sources.go` for a source,
-   etc. The field's `cfg` tag must match the `JSCK*` constant.
+   etc. The field's `cfg` tag must match the `JSCK*` constant. Add
+   `init:"hidden"` if it's only for testing.
 
 Nothing in `section.go` needs changing.
 

internal/config/conf_sections_test.go

@@ -288,6 +288,26 @@ func TestConcreteSourceSections(t *testing.T) {
 	}
 }
 
+// InitDefaults leaves out the sections tagged init:"hidden" unless asked.
+func TestInitDefaults(t *testing.T) {
+	all := InitDefaults(true)
+	shown := InitDefaults(false)
+	if all["sources.sleeper.enabled"] != false ||
+		all["sources.fts_mock.interval"] != "10m0s" {
+		t.Errorf("all = %v; want the test sources' defaults", all)
+	}
+	for key := range all {
+		hidden := strings.HasPrefix(key, "sources.fts_mock.") ||
+			strings.HasPrefix(key, "sources.sleeper.")
+		if _, found := shown[key]; found == hidden {
+			t.Errorf("%s: in the generated defaults = %v", key, found)
+		}
+	}
+	if shown["sources.eu_supply.base_url"] != "https://uk.eu-supply.com" {
+		t.Errorf("eu_supply missing: %v", shown)
+	}
+}
+
 func TestEUSupplySection(t *testing.T) {
 	conf := defaultConfig(t)
 	got := conf.Sources.EUSupply

internal/config/conf_sources.go

@@ -13,15 +13,17 @@ const JSCKSources string = "sources"
 
 // JSCSources configures each source of opportunities, one field
 // per source. Each field's cfg tag must match the section's JSCK* constant.
+// The test sources (FTSMock and Sleeper) are tagged init:"hidden", so
+// `config init` only writes them with --all.
 // SkipRulesFile is the JSON file of rules that mark new opportunities
 // Skipped (see internal/skiprules), read again when it changes; empty means
 // none.
 type JSCSources struct {
 	SkipRulesFile string               `cfg:"skip_rules_file"`
 	FindATender   JSCSourceFindATender `cfg:"find_a_tender"`
-	FTSMock       JSCSourceFTSMock     `cfg:"fts_mock"`
+	FTSMock       JSCSourceFTSMock     `cfg:"fts_mock"        init:"hidden"`
 	EUSupply      JSCSourceEUSupply    `cfg:"eu_supply"`
-	Sleeper       JSCSourceSleeper     `cfg:"sleeper"`
+	Sleeper       JSCSourceSleeper     `cfg:"sleeper"         init:"hidden"`
 }
 
 // ---------- Section methods (see Section) ----------

internal/config/config.go

@@ -40,6 +40,30 @@ func LoadDefaultConfig() {
 	LoadToViper(conf)
 }
 
+// InitDefaults returns the default configuration as dotted keys, as
+// Flatten gives it, for `config init` to write. Sections tagged
+// init:"hidden" (the test sources) are left out unless includeHidden is set.
+func InitDefaults(includeHidden bool) map[string]any {
+	var conf JobSearchConfig
+	if err := applyDefaults(&conf); err != nil {
+		panic(fmt.Sprintf("config: %v", err))
+	}
+	flat := conf.Flatten()
+	if includeHidden {
+		return flat
+	}
+
+	hidden := hiddenFromInitKeys("", reflect.TypeFor[JobSearchConfig]())
+	for _, section := range hidden {
+		for key := range flat {
+			if strings.HasPrefix(key, section+".") {
+				delete(flat, key)
+			}
+		}
+	}
+	return flat
+}
+
 // ---------- Section methods (see Section) ----------
 
 // Map implements Section.

internal/config/section.go

@@ -50,6 +50,10 @@ const (
 	keyTag = "cfg"
 	// defaultTag holds a field's default value.
 	defaultTag = "default"
+	// initTag set to initHidden on a section field leaves the section out of
+	// the file `config init` writes (see InitDefaults), as for test sources.
+	initTag    = "init"
+	initHidden = "hidden"
 )
 
 // The unknown key error and the field types section.go handles specially.
@@ -109,6 +113,8 @@ type field struct {
 	section      bool
 	defaultValue string
 	hasDefault   bool
+	// hiddenFromInit is set by initTag (see InitDefaults).
+	hiddenFromInit bool
 }
 
 // isSectionList reports whether listType is a list of sections, []S for a
@@ -146,8 +152,9 @@ func fieldsOf(structType reflect.Type) []field {
 			fieldType: structField.Type,
 			section: structField.Type.Kind() == reflect.Struct &&
 				structField.Type != timeType,
-			defaultValue: defaultValue,
-			hasDefault:   hasDefault,
+			defaultValue:   defaultValue,
+			hasDefault:     hasDefault,
+			hiddenFromInit: structField.Tag.Get(initTag) == initHidden,
 		})
 	}
 
@@ -244,6 +251,25 @@ func flattenInto(flat map[string]any, prefix string, section reflect.Value) {
 	}
 }
 
+// hiddenFromInitKeys returns the dotted keys of the sections under section
+// (prefixed with prefix, if non-empty) whose field has initTag set to
+// initHidden, descending into nested sections.
+func hiddenFromInitKeys(prefix string, sectionType reflect.Type) []string {
+	var hidden []string
+	for _, configField := range fieldsOf(sectionType) {
+		if !configField.section {
+			continue
+		}
+		key := joinKey(prefix, configField.key)
+		if configField.hiddenFromInit {
+			hidden = append(hidden, key)
+			continue
+		}
+		hidden = append(hidden, hiddenFromInitKeys(key, configField.fieldType)...)
+	}
+	return hidden
+}
+
 // exportValue returns a field's value as Map, Flatten and ValueOf give it
 // out: durations and byte sizes become strings such as "1m30s" and "32KiB",
 // so values agree with kindOf and can be passed back to SetValue; []string is