internal/codegen: cache pattern matching compilations

Type overrides are checked linearly for every codegen'd type.
That linear check currently compiles a regexp pattern for every override
that's considered. This commit adds a simple memoizing cache so that
each pattern is only ever compiled once. This dramatically improves
performance of sqlc for users who have many overrides. ngrok's usage
of sqlc generate sees a 10x speedup from this change (4s -> 0.4s).

Author: inconshreveable

internal/codegen/sdk/sdk.go

@@ -1,6 +1,8 @@
 package sdk
 
 import (
+	"sync"
+
 	"github.com/kyleconroy/sqlc/internal/pattern"
 	"github.com/kyleconroy/sqlc/internal/plugin"
 )
@@ -13,11 +15,26 @@ func DataType(n *plugin.Identifier) string {
 	}
 }
 
+var (
+	patternCache = make(map[string]*pattern.Match)
+	mu           sync.RWMutex
+)
+
 func MatchString(pat, target string) bool {
-	matcher, err := pattern.MatchCompile(pat)
-	if err != nil {
-		panic(err)
+	mu.RLock()
+	matcher, ok := patternCache[pat]
+	mu.RUnlock()
+	if !ok {
+		var err error
+		matcher, _ = pattern.MatchCompile(pat)
+		if err != nil {
+			panic(err)
+		}
+		mu.Lock()
+		patternCache[pat] = matcher
+		mu.Unlock()
 	}
+
 	return matcher.MatchString(target)
 }