lsp: Return copies of cache maps

Addressing: #750

Signed-off-by: Charlie Egan <charlie@styra.com>

internal/lsp/cache/cache.go

@@ -84,7 +84,12 @@ func (c *Cache) GetAllFiles() map[string]string {
 	c.fileContentsMu.Lock()
 	defer c.fileContentsMu.Unlock()
 
-	return c.fileContents
+	cp := make(map[string]string, len(c.fileContents))
+	for k, v := range c.fileContents {
+		cp[k] = v
+	}
+
+	return cp
 }
 
 func (c *Cache) GetFileContents(uri string) (string, bool) {
@@ -107,7 +112,12 @@ func (c *Cache) GetAllModules() map[string]*ast.Module {
 	c.moduleMu.Lock()
 	defer c.moduleMu.Unlock()
 
-	return c.modules
+	cp := make(map[string]*ast.Module, len(c.modules))
+	for k, v := range c.modules {
+		cp[k] = v
+	}
+
+	return cp
 }
 
 func (c *Cache) GetModule(uri string) (*ast.Module, bool) {
@@ -208,7 +218,12 @@ func (c *Cache) GetAllBuiltInPositions() map[string]map[uint][]types.BuiltinPosi
 	c.builtinPositionsMu.Lock()
 	defer c.builtinPositionsMu.Unlock()
 
-	return c.builtinPositionsFile
+	cp := make(map[string]map[uint][]types.BuiltinPosition, len(c.builtinPositionsFile))
+	for k, v := range c.builtinPositionsFile {
+		cp[k] = v
+	}
+
+	return cp
 }
 
 func (c *Cache) SetFileRefs(uri string, items map[string]types.Ref) {
@@ -229,7 +244,18 @@ func (c *Cache) GetAllFileRefs() map[string]map[string]types.Ref {
 	c.fileRefMu.Lock()
 	defer c.fileRefMu.Unlock()
 
-	return c.fileRefs
+	cp := make(map[string]map[string]types.Ref, len(c.fileRefs))
+
+	for k, v := range c.fileRefs {
+		innerCopy := make(map[string]types.Ref, len(v))
+		for innerK, innerV := range v {
+			innerCopy[innerK] = innerV
+		}
+
+		cp[k] = innerCopy
+	}
+
+	return cp
 }
 
 // Delete removes all cached data for a given URI.