a file's name is folded once, not once per name test

Folding is the expensive half of a name test on a name with diacritics,
and every name test of every rule folded the same name again: on Polish
names it was most of the matching work. The per-file facts memoise it,
which is where one file's work belongs - the object is per file and per
goroutine, so no lock.

  4000 Polish names, twelve rules with name tests: 0.33s -> 0.13s

2 files changed, 10 insertions, 1 deletions

diff --git a/internal/cond/eval.go b/internal/cond/eval.go
index 2ae31fb..7d8e00d 100644
--- a/internal/cond/eval.go
+++ b/internal/cond/eval.go
@@ -28,6 +28,12 @@ type Facts interface {
 	// an earlier rule could not be decided (its condition was unknown): with
 	// no match and an undecided rule, (matched) is unknown.
 	Matched() (matched, undecided bool)
+	// Folded is norm.FoldMapped(subj), memoised per file. Folding is the
+	// expensive half of a name test on a name with diacritics, and the
+	// same name is folded again by every name test of every rule; the
+	// implementation holds one file at a time, so a small memo there
+	// removes the repetition entirely.
+	Folded(subj string) norm.Folded
 }
 
 // Result is the outcome of evaluating a Cond against one file's Facts.
@@ -243,7 +249,7 @@ func (c *Cond) evalLeaf(n *node, f Facts) (ok bool, reason, warn string, caps []
 		// back from the original, so {1} keeps the name's diacritics.
 		folded := norm.Folded{Text: subj}
 		if c.opt.Fold {
-			folded = norm.FoldMapped(subj)
+			folded = f.Folded(subj)
 		}
 		for _, p := range n.patterns {
 			loc := p.re.FindStringSubmatchIndex(folded.Text)
diff --git a/internal/cond/eval_test.go b/internal/cond/eval_test.go
index 5074557..7f06afd 100644
--- a/internal/cond/eval_test.go
+++ b/internal/cond/eval_test.go
@@ -39,6 +39,9 @@ func (f *fake) Size() int64           { return f.size }
 func (f *fake) ModTime() time.Time    { return now.Add(-f.age) }
 func (f *fake) Now() time.Time        { return now }
 func (f *fake) Matched() (bool, bool) { return f.matched, f.matchedUnknown }
+
+// Folded has no memo here: a fake stands in for one file in one test.
+func (f *fake) Folded(subj string) norm.Folded { return norm.FoldMapped(subj) }
 func (f *fake) ContentContains(opt Options, keywords []string) (int, error) {
 	f.contentCalls++
 	if f.rawErr != nil {