feat: support presence checks in conditional rules

Signed-off-by: Joseph Kato <joseph@jdkato.io>

Author: jdkato

internal/check/conditional.go

@@ -1,6 +1,8 @@
 package check
 
 import (
+	"strings"
+
 	"github.com/errata-ai/regexp2"
 
 	"github.com/errata-ai/vale/v3/internal/core"
@@ -18,6 +20,21 @@ type Conditional struct {
 	phraseRe   *regexp2.Regexp
 	Ignorecase bool
 	Vocab      bool
+
+	// secondHasGroup records whether `Second` has a capture group. When it
+	// does, a `First` match is allowed only if its value was captured by a
+	// `Second` match (e.g. an acronym defined as `... (WHO)`). When it doesn't,
+	// the rule is a plain presence check: any `First` requires `Second` to
+	// appear somewhere in the same block. See #1048.
+	secondHasGroup bool
+}
+
+// hasCaptureGroup reports whether `pattern` contains a capturing group -- an
+// unescaped `(` that doesn't begin a non-capturing/extension group `(?...)`.
+func hasCaptureGroup(pattern string) bool {
+	opens := strings.Count(pattern, "(")
+	noncap := strings.Count(pattern, "(?") + strings.Count(pattern, `\(`)
+	return opens > noncap
 }
 
 // NewConditional creates a new `conditional`-based rule.
@@ -47,6 +64,7 @@ func NewConditional(cfg *core.Config, generic baseCheck, path string) (Condition
 		return rule, core.NewE201FromPosition(err.Error(), path, 1)
 	}
 	expression = append(expression, re)
+	rule.secondHasGroup = hasCaptureGroup(rule.Second)
 
 	re, err = regexp2.CompileStd(rule.First)
 	if err != nil {
@@ -64,6 +82,18 @@ func (c Conditional) Run(blk nlp.Block, f *core.File, cfg *core.Config) ([]core.
 	alerts := []core.Alert{}
 
 	txt := blk.Text
+
+	// When `Second` has no capture group, the rule is a plain presence check:
+	// if `First` appears, `Second` must appear somewhere in the same block. If
+	// it does, there's nothing to flag; otherwise every `First` match is a
+	// violation. See #1048.
+	if !c.secondHasGroup {
+		if c.patterns[0].MatchStringStd(txt) {
+			return alerts, nil
+		}
+		return c.flagAntecedents(txt, cfg)
+	}
+
 	// We first look for the consequent of the conditional statement.
 	// For example, if we're ensuring that abbreviations have been defined
 	// parenthetically, we'd have something like:
@@ -107,6 +137,29 @@ func (c Conditional) Run(blk nlp.Block, f *core.File, cfg *core.Config) ([]core.
 	return alerts, nil
 }
 
+// flagAntecedents reports every `First` match as a violation (used by the
+// presence check when `Second` is absent), honoring the rule's exceptions and
+// accepted phrases.
+func (c Conditional) flagAntecedents(txt string, cfg *core.Config) ([]core.Alert, error) {
+	alerts := []core.Alert{}
+	for _, loc := range c.patterns[1].FindAllStringIndex(txt, -1) {
+		s, err := re2Loc(txt, loc)
+		if err != nil {
+			return alerts, err
+		}
+		if isMatch(c.exceptRe, s) || withinPhrase(c.phraseRe, txt, loc) {
+			continue
+		}
+
+		a, erra := makeAlert(c.Definition, loc, txt, cfg)
+		if erra != nil {
+			return alerts, erra
+		}
+		alerts = append(alerts, a)
+	}
+	return alerts, nil
+}
+
 // Fields provides access to the internal rule definition.
 func (c Conditional) Fields() Definition {
 	return c.Definition

testdata/features/checks.feature

@@ -22,6 +22,15 @@ Feature: Checks
             test.md:9:5:Checks.MultiCapture:'NFL' has no definition
             """
 
+    Scenario: Conditional presence check (#1048)
+        # When `second` has no capture group, the rule just requires `second` to
+        # be present whenever `first` is -- so only the file missing it flags.
+        When I test "checks/ConditionalPresence"
+        Then the output should contain exactly:
+            """
+            missing.md:1:3:Test.Presence:A 'Section' requires a 'Summary:' line.
+            """
+
     Scenario: Occurrence
         When I test "checks/Occurrence"
         Then the output should contain exactly:

testdata/fixtures/checks/ConditionalPresence/.vale.ini

@@ -0,0 +1,5 @@
+StylesPath = styles
+MinAlertLevel = suggestion
+
+[*.md]
+BasedOnStyles = Test

testdata/fixtures/checks/ConditionalPresence/has.md

@@ -0,0 +1,3 @@
+# Section
+
+Summary: this is present.

testdata/fixtures/checks/ConditionalPresence/missing.md

@@ -0,0 +1,3 @@
+# Section
+
+No summary line here.

testdata/fixtures/checks/ConditionalPresence/styles/Test/Presence.yml

@@ -0,0 +1,6 @@
+extends: conditional
+message: "A 'Section' requires a 'Summary:' line."
+level: error
+scope: raw
+first: '\bSection\b'
+second: 'Summary:'