Don't force multiline interpolation into a single line (#1280)

Also, fixes an issue where forced single-line formatting would break for if/else
and let expressions

---------

Co-authored-by: Islon Scherer <islonscherer@gmail.com>

docs/modules/release-notes/pages/0.30.adoc

@@ -25,7 +25,7 @@ To get started, follow xref:pkl-cli:index.adoc#installation[Installation].#
 [[formatter]]
 === Formatter
 
-Pkl now has a formatter (https://github.com/apple/pkl/pull/1107[#1107], https://github.com/apple/pkl/pull/1208[#1208], https://github.com/apple/pkl/pull/1211[#1211], https://github.com/apple/pkl/pull/1215[#1215], https://github.com/apple/pkl/pull/1217[#1217], https://github.com/apple/pkl/pull/1235[#1235], https://github.com/apple/pkl/pull/1246[#1246], https://github.com/apple/pkl/pull/1247[#1247], https://github.com/apple/pkl/pull/1252[#1252], https://github.com/apple/pkl/pull/1256[#1256], https://github.com/apple/pkl/pull/1259[#1259], https://github.com/apple/pkl/pull/1260[#1260], https://github.com/apple/pkl/pull/1263[#1263], https://github.com/apple/pkl/pull/1265[#1265], https://github.com/apple/pkl/pull/1266[#1266], https://github.com/apple/pkl/pull/1267[#1267], https://github.com/apple/pkl/pull/1270[#1270], https://github.com/apple/pkl/pull/1271[#1271], https://github.com/apple/pkl/pull/1272[#1272], https://github.com/apple/pkl/pull/1273[#1273], https://github.com/apple/pkl/pull/1274[#1274])!
+Pkl now has a formatter (https://github.com/apple/pkl/pull/1107[#1107], https://github.com/apple/pkl/pull/1208[#1208], https://github.com/apple/pkl/pull/1211[#1211], https://github.com/apple/pkl/pull/1215[#1215], https://github.com/apple/pkl/pull/1217[#1217], https://github.com/apple/pkl/pull/1235[#1235], https://github.com/apple/pkl/pull/1246[#1246], https://github.com/apple/pkl/pull/1247[#1247], https://github.com/apple/pkl/pull/1252[#1252], https://github.com/apple/pkl/pull/1256[#1256], https://github.com/apple/pkl/pull/1259[#1259], https://github.com/apple/pkl/pull/1260[#1260], https://github.com/apple/pkl/pull/1263[#1263], https://github.com/apple/pkl/pull/1265[#1265], https://github.com/apple/pkl/pull/1266[#1266], https://github.com/apple/pkl/pull/1267[#1267], https://github.com/apple/pkl/pull/1270[#1270], https://github.com/apple/pkl/pull/1271[#1271], https://github.com/apple/pkl/pull/1272[#1272], https://github.com/apple/pkl/pull/1273[#1273], https://github.com/apple/pkl/pull/1274[#1274], https://github.com/apple/pkl/pull/1280[#1280])!
 
 Pkl's formatter is _canonical_, which means that it has a single set of formatting rules, with (almost) no configuration options.
 The goal is to eliminate the possibility of formatting debates, which can lead to churn and bike-shedding.

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

@@ -39,8 +39,6 @@ internal class Builder(sourceText: String, private val grammarVersion: GrammarVe
   private var prevNode: Node? = null
   private var noNewlines = false
 
-  private class CannotAvoidNewline : RuntimeException()
-
   fun format(node: Node): FormatNode {
     prevNode = node
     return when (node.type) {
@@ -836,16 +834,10 @@ internal class Builder(sourceText: String, private val grammarVersion: GrammarVe
       while (cursor.hasNext()) {
         if (isInStringInterpolation) {
           val prevNoNewlines = noNewlines
-          noNewlines = true
           val elems = cursor.takeUntilBefore { it.isTerminal(")") }
+          noNewlines = !elems.isMultiline()
           getBaseSeparator(prev!!, elems.first())?.let { add(it) }
-          val formatted =
-            try {
-              formatGeneric(elems, null)
-            } catch (_: CannotAvoidNewline) {
-              noNewlines = false
-              formatGeneric(elems, null)
-            }
+          val formatted = formatGeneric(elems, null)
           addAll(formatted)
           getBaseSeparator(elems.last(), cursor.peek())?.let { add(it) }
           noNewlines = prevNoNewlines
@@ -872,7 +864,7 @@ internal class Builder(sourceText: String, private val grammarVersion: GrammarVe
   }
 
   private fun formatIf(node: Node): FormatNode {
-    val separator = if (node.isMultiline()) forceLine() else spaceOrLine()
+    val separator = if (node.isMultiline()) forceSpaceyLine() else spaceOrLine()
     val nodes =
       formatGeneric(node.children) { _, next ->
         // produce `else if` in the case of nested if.
@@ -971,7 +963,7 @@ internal class Builder(sourceText: String, private val grammarVersion: GrammarVe
   }
 
   private fun formatLetExpr(node: Node): FormatNode {
-    val separator = if (node.isMultiline()) forceLine() else spaceOrLine()
+    val separator = if (node.isMultiline()) forceSpaceyLine() else spaceOrLine()
     val endsWithLet = node.children.last().type == NodeType.LET_EXPR
     val nodes =
       formatGenericWithGen(
@@ -1315,7 +1307,12 @@ internal class Builder(sourceText: String, private val grammarVersion: GrammarVe
   }
 
   private fun mustForceLine(): FormatNode {
-    return if (noNewlines) throw CannotAvoidNewline() else ForceLine
+    if (noNewlines) {
+      // should never happen; we do not set `noNewlines` for interpolation blocks that span multiple
+      // lines
+      throw RuntimeException("Tried to render Pkl code as single line")
+    }
+    return ForceLine
   }
 
   private fun forceLine(): FormatNode {
@@ -1460,6 +1457,9 @@ internal class Builder(sourceText: String, private val grammarVersion: GrammarVe
 
   private fun Node.isMultiline(): Boolean = span.lineBegin < span.lineEnd
 
+  private fun List<Node>.isMultiline(): Boolean =
+    if (isEmpty()) false else first().span.lineBegin < last().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/string-interpolation.pkl

@@ -13,7 +13,7 @@ prop3 =
   \(new {
     // some comment
     foo = 1
-    
+
     // some comment
     bar = 2
   })
@@ -49,3 +49,28 @@ prop7 = "\(
 )"
 
 prop8 = "\(new { foo = 1 bar = 2 baz = 3 })"
+
+prop9 = "\(if (true) 1 else 2)"
+
+prop10 = "\(
+  if (true) 1
+  else 2
+)"
+
+prop11 = "\(
+  new {
+    1;
+    2;
+    3;
+  }
+)"
+
+// single line expressions are not broken up
+prop12 = "Some \(if (true) 1 else 2) reeeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaallly long string with interpolation"
+
+// multi-line expressions are preserved
+prop13 = "Some \(
+  if (true)
+    1
+  else 2
+  ) reeeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaallly long string with interpolation"

pkl-formatter/src/test/files/FormatterSnippetTests/output/multi-line-strings.pkl

@@ -1,6 +1,8 @@
 foo =
   """
-  asd \(new { bar = 1 }) asd
+  asd \(new {
+    bar = 1
+  }) asd
   """
 
 bar =

pkl-formatter/src/test/files/FormatterSnippetTests/output/string-interpolation.pkl

@@ -50,3 +50,29 @@ prop7 =
   )"
 
 prop8 = "\(new { foo = 1; bar = 2; baz = 3 })"
+
+prop9 = "\(if (true) 1 else 2)"
+
+prop10 =
+  "\(if (true)
+    1
+  else
+    2)"
+
+prop11 =
+  "\(new {
+    1
+    2
+    3
+  })"
+
+// single line expressions are not broken up
+prop12 =
+  "Some \(if (true) 1 else 2) reeeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaallly long string with interpolation"
+
+// multi-line expressions are preserved
+prop13 =
+  "Some \(if (true)
+    1
+  else
+    2) reeeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaallly long string with interpolation"