Add CODEC/compression expression support in EXPLAIN output (#86)

Author: kyleconroy

internal/explain/explain.go

@@ -197,6 +197,9 @@ func Column(sb *strings.Builder, col *ast.ColumnDeclaration, depth int) {
 	if col.Default != nil || hasEphemeralDefault {
 		children++
 	}
+	if col.Codec != nil {
+		children++
+	}
 	fmt.Fprintf(sb, "%sColumnDeclaration %s (children %d)\n", indent, col.Name, children)
 	if col.Type != nil {
 		Node(sb, col.Type, depth+1)
@@ -207,6 +210,34 @@ func Column(sb *strings.Builder, col *ast.ColumnDeclaration, depth int) {
 		// EPHEMERAL columns without explicit default value show defaultValueOfTypeName function
 		fmt.Fprintf(sb, "%s Function defaultValueOfTypeName\n", indent)
 	}
+	if col.Codec != nil {
+		explainCodecExpr(sb, col.Codec, indent+" ", depth+1)
+	}
+}
+
+// explainCodecExpr handles CODEC expressions in column declarations
+func explainCodecExpr(sb *strings.Builder, codec *ast.CodecExpr, indent string, depth int) {
+	// CODEC is rendered as a Function with one child (ExpressionList of codecs)
+	fmt.Fprintf(sb, "%sFunction CODEC (children 1)\n", indent)
+	fmt.Fprintf(sb, "%s ExpressionList (children %d)\n", indent, len(codec.Codecs))
+	for _, c := range codec.Codecs {
+		explainCodecFunction(sb, c, indent+"  ", depth+2)
+	}
+}
+
+// explainCodecFunction handles individual codec functions (e.g., LZ4, ZSTD(10), Gorilla(1))
+func explainCodecFunction(sb *strings.Builder, fn *ast.FunctionCall, indent string, depth int) {
+	if len(fn.Arguments) == 0 {
+		// Codec without parameters: just the function name
+		fmt.Fprintf(sb, "%sFunction %s\n", indent, fn.Name)
+	} else {
+		// Codec with parameters: function with ExpressionList of arguments
+		fmt.Fprintf(sb, "%sFunction %s (children 1)\n", indent, fn.Name)
+		fmt.Fprintf(sb, "%s ExpressionList (children %d)\n", indent, len(fn.Arguments))
+		for _, arg := range fn.Arguments {
+			Node(sb, arg, depth+2)
+		}
+	}
 }
 
 func Index(sb *strings.Builder, idx *ast.IndexDefinition, depth int) {

parser/testdata/00162_mmap_compression_none/metadata.json

@@ -1 +1 @@
-{"explain_todo":{"stmt2":true}}
+{}

parser/testdata/00804_test_alter_compression_codecs/metadata.json

@@ -5,14 +5,8 @@
     "stmt20": true,
     "stmt21": true,
     "stmt27": true,
-    "stmt3": true,
-    "stmt30": true,
-    "stmt31": true,
-    "stmt32": true,
-    "stmt36": true,
     "stmt41": true,
     "stmt43": true,
-    "stmt7": true,
     "stmt8": true
   }
 }

parser/testdata/00804_test_custom_compression_codecs/metadata.json

@@ -1,17 +1 @@
-{
-  "explain_todo": {
-    "stmt22": true,
-    "stmt23": true,
-    "stmt24": true,
-    "stmt25": true,
-    "stmt26": true,
-    "stmt27": true,
-    "stmt28": true,
-    "stmt38": true,
-    "stmt4": true,
-    "stmt49": true,
-    "stmt50": true,
-    "stmt58": true,
-    "stmt69": true
-  }
-}
+{}

parser/testdata/00804_test_custom_compression_codes_log_storages/metadata.json

@@ -1,8 +1 @@
-{
-  "explain_todo": {
-    "stmt16": true,
-    "stmt28": true,
-    "stmt4": true,
-    "stmt40": true
-  }
-}
+{}

parser/testdata/00804_test_deflate_qpl_codec_compression/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt4": true
-  }
-}
+{}

parser/testdata/00804_test_delta_codec_compression/metadata.json

@@ -1,14 +1,8 @@
 {
   "explain_todo": {
     "stmt12": true,
-    "stmt18": true,
-    "stmt19": true,
     "stmt20": true,
     "stmt24": true,
-    "stmt30": true,
-    "stmt31": true,
-    "stmt36": true,
-    "stmt5": true,
-    "stmt6": true
+    "stmt36": true
   }
 }

parser/testdata/00804_test_delta_codec_no_type_alter/metadata.json

@@ -1 +1,8 @@
-{"explain_todo":{"stmt4":true,"stmt5":true,"stmt6":true,"stmt7":true,"stmt8":true,"stmt9":true}}
+{
+  "explain_todo": {
+    "stmt5": true,
+    "stmt6": true,
+    "stmt7": true,
+    "stmt9": true
+  }
+}

parser/testdata/00804_test_zstd_qat_codec_compression/metadata.json

@@ -1,7 +1 @@
-{
-  "explain_todo": {
-    "stmt4": true,
-    "stmt5": true,
-    "stmt6": true
-  }
-}
+{}

parser/testdata/00870_t64_codec/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt2": true
-  }
-}
+{}