Router: implement binPack.indentCallSiteSingleArg

docs/configuration.md

@@ -627,6 +627,60 @@ maxColumn = 20
 foo(bar1(baz1(qux1, qux2), baz2), bar2(baz3, baz4))
 ```
 
+#### `binPack.indentCallSiteSingleArg`
+
+When this parameter is disabled, no indentation is added for same-line single-arg
+cases; the assumption is that if the argument expression spans multiple lines,
+it will introduce its own indentation.
+
+```scala mdoc:defaults
+binPack.indentCallSiteSingleArg
+```
+
+With the parameter enabled:
+
+```scala mdoc:scalafmt
+binPack.unsafeCallSite = true
+binPack.indentCallSiteSingleArg = true
+indent.callSite = 2
+maxColumn = 20
+---
+foo(bar(baz.qux(xyz + zyx)))
+foo(bar((_, _) =>
+  baz { qux =>
+    noop
+  } baz { qux =>
+    noop
+  } baz //
+    { qux =>
+      noop
+    } baz { qux =>
+      noop
+    }))
+```
+
+With the parameter disabled:
+
+```scala mdoc:scalafmt
+binPack.unsafeCallSite = true
+binPack.indentCallSiteSingleArg = false
+indent.callSite = 2
+maxColumn = 20
+---
+foo(bar(baz.qux(xyz + zyx)))
+foo(bar((_, _) =>
+  baz { qux =>
+    noop
+  } baz { qux =>
+    noop
+  } baz //
+    { qux =>
+      noop
+    } baz { qux =>
+      noop
+    }))
+```
+
 ### `indentOperator`
 
 Normally, the first eligible break _inside_ a chain of infix operators is

scalafmt-core/shared/src/main/scala/org/scalafmt/config/BinPack.scala

@@ -35,6 +35,7 @@ case class BinPack(
     private val bracketCallSite: Option[BinPack.Unsafe] = None,
     private val bracketDefnSite: Option[BinPack.Unsafe] = None,
     indentCallSiteOnce: Boolean = false,
+    indentCallSiteSingleArg: Boolean = true,
     parentConstructors: BinPack.ParentCtors = BinPack.ParentCtors.source,
     literalArgumentLists: Boolean = true,
     literalsIncludeSimpleExpr: Boolean = false,

scalafmt-core/shared/src/main/scala/org/scalafmt/internal/Router.scala

@@ -1300,6 +1300,7 @@ class Router(formatOps: FormatOps) {
           !isBracket && getAssignAtSingleArgCallSite(leftOwner).isDefined
         val noSplitIndents =
           if (noNoSplitIndents) Nil
+          else if (isSingleArg && !style.binPack.indentCallSiteSingleArg) Nil
           else if (style.binPack.indentCallSiteOnce) {
             @tailrec
             def iter(tree: Tree): Option[T] = tree.parent match {
@@ -1349,7 +1350,7 @@ class Router(formatOps: FormatOps) {
                 SingleLineBlock(slbEnd, noSyntaxNL = true)
               }
             } else penalizeNewlinesPolicy
-            val indentOncePolicy =
+            def indentOncePolicy =
               if (style.binPack.indentCallSiteOnce) {
                 val trigger = getIndentTrigger(leftOwner)
                 Policy.on(close) {
@@ -1362,7 +1363,7 @@ class Router(formatOps: FormatOps) {
               .withOptimalTokenOpt(opt)
               .withPolicy(noSplitPolicy)
               .andPolicy(unindentPolicy, !isSingleArg || noSplitIndents.isEmpty)
-              .andPolicy(indentOncePolicy)
+              .andPolicy(indentOncePolicy, noSplitIndents.isEmpty)
           }
 
         val nlPolicy = {

scalafmt-tests/src/test/resources/default/Apply.stat

@@ -1948,9 +1948,10 @@ class a {
     maxIdleDuration = Duration.Inf
   )(F)
 }
-<<< binPack unsafeCallSite, !indentOnce
+<<< binPack unsafeCallSite, !indentOnce, indentCallSiteSingleArg
 binPack.unsafeCallSite = always
 binPack.indentCallSiteOnce = false
+binPack.indentCallSiteSingleArg = true
 indent.callSite = 2
 align.preset = none
 ===
@@ -1981,9 +1982,10 @@ object a {
           noop4
         }))
 }
-<<< binPack unsafeCallSite, indentOnce
+<<< binPack unsafeCallSite, indentOnce, indentCallSiteSingleArg
 binPack.unsafeCallSite = always
 binPack.indentCallSiteOnce = true
+binPack.indentCallSiteSingleArg = true
 indent.callSite = 2
 align.preset = none
 ===
@@ -2014,3 +2016,37 @@ object a {
           noop4
         }))
 }
+<<< binPack unsafeCallSite, indentOnce, !indentCallSiteSingleArg
+binPack.unsafeCallSite = always
+binPack.indentCallSiteOnce = true
+binPack.indentCallSiteSingleArg = false
+indent.callSite = 2
+align.preset = none
+===
+object a {
+  val ref = foo(bar((_, _) =>
+    baz1 { qux1 =>
+      noop1
+    } baz2 { qux2 =>
+      noop2
+    } baz3 //
+      { qux3 =>
+        noop3
+      } baz4 { qux4 =>
+        noop4
+      }))
+}
+>>>
+object a {
+  val ref = foo(bar((_, _) =>
+    baz1 { qux1 =>
+      noop1
+    } baz2 { qux2 =>
+      noop2
+    } baz3 //
+      { qux3 =>
+        noop3
+      } baz4 { qux4 =>
+        noop4
+      }))
+}