Adds configurable AST -> SQL printer (#1183)

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Adds overridden `toString()` method for Sprout-generated code.
 - Adds CURRENT_DATE session variable to PartiQL.g4 and PartiQLParser
+- Adds configurable AST to SQL pretty printer. Usage in Java `AstKt.sql(ast)` or in Kotlin `ast.sql()`.
 
 ### Changed
 

partiql-ast/src/main/kotlin/org/partiql/ast/Ast.kt

@@ -1,6 +1,10 @@
 package org.partiql.ast
 
 import org.partiql.ast.builder.AstFactoryImpl
+import org.partiql.ast.sql.SqlBlock
+import org.partiql.ast.sql.SqlDialect
+import org.partiql.ast.sql.SqlLayout
+import org.partiql.ast.sql.sql
 
 /**
  * Singleton instance of the default factory; also accessible via `AstFactory.DEFAULT`.
@@ -13,3 +17,12 @@ object Ast : AstBaseFactory()
 public abstract class AstBaseFactory : AstFactoryImpl() {
     // internal default overrides here
 }
+
+/**
+ * Pretty-print this [AstNode] as SQL text with the given [SqlLayout]
+ */
+@JvmOverloads
+public fun AstNode.sql(
+    layout: SqlLayout = SqlLayout.DEFAULT,
+    dialect: SqlDialect = SqlDialect.PARTIQL,
+): String = accept(dialect, SqlBlock.Nil).sql(layout)

partiql-ast/src/main/kotlin/org/partiql/ast/sql/Sql.kt

@@ -0,0 +1,39 @@
+package org.partiql.ast.sql
+
+// a <> b  <-> a concat b
+
+internal infix fun SqlBlock.concat(rhs: SqlBlock): SqlBlock = link(this, rhs)
+
+internal infix fun SqlBlock.concat(text: String): SqlBlock = link(this, text(text))
+
+internal infix operator fun SqlBlock.plus(rhs: SqlBlock): SqlBlock = link(this, rhs)
+
+internal infix operator fun SqlBlock.plus(text: String): SqlBlock = link(this, text(text))
+
+// Shorthand
+
+internal val NIL = SqlBlock.Nil
+
+internal val NL = SqlBlock.NL
+
+internal fun text(text: String) = SqlBlock.Text(text)
+
+internal fun link(lhs: SqlBlock, rhs: SqlBlock) = SqlBlock.Link(lhs, rhs)
+
+internal fun nest(block: () -> SqlBlock) = SqlBlock.Nest(block())
+
+internal fun list(start: String?, end: String?, delimiter: String? = ",", items: () -> List<SqlBlock>): SqlBlock {
+    var h: SqlBlock = NIL
+    h = if (start != null) h + start else h
+    h += nest {
+        val kids = items()
+        var list: SqlBlock = NIL
+        kids.foldIndexed(list) { i, a, item ->
+            list += item
+            list = if (delimiter != null && (i + 1) < kids.size) a + delimiter else a
+            list
+        }
+    }
+    h = if (end != null) h + end else h
+    return h
+}

partiql-ast/src/main/kotlin/org/partiql/ast/sql/SqlBlock.kt

@@ -0,0 +1,89 @@
+package org.partiql.ast.sql
+
+/**
+ * Write this [SqlBlock] tree as SQL text with the given [SqlLayout].
+ *
+ * @param layout    SQL formatting ruleset
+ * @return SQL text
+ */
+public fun SqlBlock.sql(layout: SqlLayout = SqlLayout.DEFAULT): String = layout.format(this)
+
+/**
+ * Representation of some textual corpus; akin to Wadler's "A prettier printer" Document type.
+ */
+sealed interface SqlBlock {
+
+    public override fun toString(): String
+
+    public fun <R, C> accept(visitor: BlockVisitor<R, C>, ctx: C): R
+
+    public object Nil : SqlBlock {
+
+        override fun toString() = ""
+
+        override fun <R, C> accept(visitor: BlockVisitor<R, C>, ctx: C): R = visitor.visitNil(this, ctx)
+    }
+
+    public object NL : SqlBlock {
+
+        override fun toString() = "\n"
+
+        override fun <R, C> accept(visitor: BlockVisitor<R, C>, ctx: C): R = visitor.visitNewline(this, ctx)
+    }
+
+    public class Text(val text: String) : SqlBlock {
+
+        override fun toString() = text
+
+        override fun <R, C> accept(visitor: BlockVisitor<R, C>, ctx: C): R = visitor.visitText(this, ctx)
+    }
+
+    public class Nest(val child: SqlBlock) : SqlBlock {
+
+        override fun toString() = child.toString()
+
+        override fun <R, C> accept(visitor: BlockVisitor<R, C>, ctx: C): R = visitor.visitNest(this, ctx)
+    }
+
+    // Use link block rather than linked-list block.next as it makes pre-order traversal trivial
+    public class Link(val lhs: SqlBlock, val rhs: SqlBlock) : SqlBlock {
+
+        override fun toString() = lhs.toString() + rhs.toString()
+
+        override fun <R, C> accept(visitor: BlockVisitor<R, C>, ctx: C): R = visitor.visitLink(this, ctx)
+    }
+}
+
+public interface BlockVisitor<R, C> {
+
+    public fun visit(block: SqlBlock, ctx: C): R
+
+    public fun visitNil(block: SqlBlock.Nil, ctx: C): R
+
+    public fun visitNewline(block: SqlBlock.NL, ctx: C): R
+
+    public fun visitText(block: SqlBlock.Text, ctx: C): R
+
+    public fun visitNest(block: SqlBlock.Nest, ctx: C): R
+
+    public fun visitLink(block: SqlBlock.Link, ctx: C): R
+}
+
+public abstract class BlockBaseVisitor<R, C> : BlockVisitor<R, C> {
+
+    public abstract fun defaultReturn(block: SqlBlock, ctx: C): R
+
+    public open fun defaultVisit(block: SqlBlock, ctx: C) = defaultReturn(block, ctx)
+
+    public override fun visit(block: SqlBlock, ctx: C): R = block.accept(this, ctx)
+
+    public override fun visitNil(block: SqlBlock.Nil, ctx: C): R = defaultVisit(block, ctx)
+
+    public override fun visitNewline(block: SqlBlock.NL, ctx: C): R = defaultVisit(block, ctx)
+
+    public override fun visitText(block: SqlBlock.Text, ctx: C): R = defaultVisit(block, ctx)
+
+    public override fun visitNest(block: SqlBlock.Nest, ctx: C): R = defaultVisit(block, ctx)
+
+    public override fun visitLink(block: SqlBlock.Link, ctx: C): R = defaultVisit(block, ctx)
+}