Respect newlines in if/else and let expressions (#1259)

Change the formatter to prevent multiline if/else and let expressions
from collapsing into a single line.

pkl-formatter/src/main/kotlin/org/pkl/formatter/Builder.kt

@@ -872,11 +872,14 @@ internal class Builder(sourceText: String, private val grammarVersion: GrammarVe
   }
 
   private fun formatIf(node: Node): FormatNode {
+    val separator = if (node.isMultiline()) forceLine() else spaceOrLine()
     val nodes =
       formatGeneric(node.children) { _, next ->
-        if (next.type == NodeType.IF_ELSE_EXPR && next.children[0].type == NodeType.IF_EXPR) {
-          Space
-        } else spaceOrLine()
+        // produce `else if` in the case of nested if.
+        // note: don't need to handle if `next.children[0]` is an affix because that can't be
+        // emitted as `else if` anyway.
+        if (next.type == NodeType.IF_ELSE_EXPR && next.children[0].type == NodeType.IF_EXPR) Space
+        else separator
       }
     return Group(newId(), nodes)
   }
@@ -968,10 +971,11 @@ internal class Builder(sourceText: String, private val grammarVersion: GrammarVe
   }
 
   private fun formatLetExpr(node: Node): FormatNode {
+    val separator = if (node.isMultiline()) forceLine() else spaceOrLine()
     val nodes =
       formatGenericWithGen(
         node.children,
-        { _, next -> if (next.type == NodeType.LET_PARAMETER_DEFINITION) Space else spaceOrLine() },
+        { _, next -> if (next.type == NodeType.LET_PARAMETER_DEFINITION) Space else separator },
       ) { node, next ->
         if (next == null) {
           if (node.type == NodeType.LET_EXPR) {
@@ -1323,7 +1327,7 @@ internal class Builder(sourceText: String, private val grammarVersion: GrammarVe
   }
 
   private fun hasTrailingAffix(node: Node, next: Node): Boolean {
-    if (node.span.lineEnd < next.span.lineBegin) return false
+    if (node.isMultiline()) return false
     var n: Node? = next
     while (n != null) {
       if (n.type.isAffix && node.span.lineEnd == n.span.lineBegin) return true
@@ -1450,6 +1454,8 @@ internal class Builder(sourceText: String, private val grammarVersion: GrammarVe
   // returns true if this node is not an affix or terminal
   private fun Node.isProper(): Boolean = !type.isAffix && type != NodeType.TERMINAL
 
+  private fun Node.isMultiline(): Boolean = span.lineBegin < span.lineEnd
+
   private inline fun <T> List<T>.splitOn(pred: (T) -> Boolean): Pair<List<T>, List<T>> {
     val index = indexOfFirst { pred(it) }
     return if (index == -1) {

pkl-formatter/src/test/files/FormatterSnippetTests/input/expr-if.pkl

@@ -5,3 +5,29 @@ foo =
     else
       if (someAnotherCondition) 30000
       else 4
+
+foo2 = if (bar) 1 else 2
+
+// respect newlines in if/else if they exist.
+// if anything of these wrap, everything wraps.
+foo3 =
+  if (bar)
+    1 else 2
+
+foo4 =
+  if (bar) 1 else 
+    2
+
+foo5 =
+  if (bar) 1
+  else 2
+
+foo6 =
+  if (bar)
+    1
+  else
+    2
+
+foo7 =
+  if /* some comment */ (bar) 1
+  else 2

pkl-formatter/src/test/files/FormatterSnippetTests/input/expr-let.pkl

@@ -15,3 +15,11 @@ qux = let ( // some comment
     bar = 5
   )
     bar
+
+quzzy =
+  let (baz = 1) baz + 1
+
+// respect newlines in lets
+quzzzy =
+  let (baz = 1)
+    baz + 1

pkl-formatter/src/test/files/FormatterSnippetTests/output/expr-if.pkl

@@ -7,3 +7,37 @@ foo =
     30000
   else
     4
+
+foo2 = if (bar) 1 else 2
+
+// respect newlines in if/else if they exist.
+// if anything of these wrap, everything wraps.
+foo3 =
+  if (bar)
+    1
+  else
+    2
+
+foo4 =
+  if (bar)
+    1
+  else
+    2
+
+foo5 =
+  if (bar)
+    1
+  else
+    2
+
+foo6 =
+  if (bar)
+    1
+  else
+    2
+
+foo7 =
+  if /* some comment */ (bar)
+    1
+  else
+    2

pkl-formatter/src/test/files/FormatterSnippetTests/output/expr-let.pkl

@@ -25,3 +25,10 @@ qux =
     bar = 5
   )
     bar
+
+quzzy = let (baz = 1) baz + 1
+
+// respect newlines in lets
+quzzzy =
+  let (baz = 1)
+    baz + 1