Pattern match support in checking global objects (#18127)

Pattern match in checking global objects

compiler/src/dotty/tools/dotc/transform/init/Objects.scala

@@ -6,15 +6,18 @@ import core.*
 import Contexts.*
 import Symbols.*
 import Types.*
+import Denotations.Denotation
 import StdNames.*
+import Names.TermName
 import NameKinds.OuterSelectName
 import NameKinds.SuperAccessorName
 
 import ast.tpd.*
-import util.SourcePosition
+import util.{ SourcePosition, NoSourcePosition }
 import config.Printers.init as printer
 import reporting.StoreReporter
 import reporting.trace as log
+import typer.Applications.*
 
 import Errors.*
 import Trace.*
@@ -249,7 +252,7 @@ object Objects:
           val joinedTrace = data.pendingTraces.slice(index + 1, data.checkingObjects.size).foldLeft(pendingTrace) { (a, acc) => acc ++ a }
           val callTrace = Trace.buildStacktrace(joinedTrace, "Calling trace:\n")
           val cycle = data.checkingObjects.slice(index, data.checkingObjects.size)
-          val pos = clazz.defTree
+          val pos = clazz.defTree.sourcePos.focus
           report.warning("Cyclic initialization: " + cycle.map(_.klass.show).mkString(" -> ") + " -> " + clazz.show + ". " + callTrace, pos)
         end if
         data.checkingObjects(index)
@@ -834,11 +837,10 @@ object Objects:
 
   /** Handle local variable definition, `val x = e` or `var x = e`.
    *
-   * @param ref          The value for `this` where the variable is defined.
    * @param sym          The symbol of the variable.
    * @param value        The value of the initializer.
    */
-  def initLocal(ref: Ref, sym: Symbol, value: Value): Contextual[Unit] = log("initialize local " + sym.show + " with " + value.show, printer) {
+  def initLocal(sym: Symbol, value: Value): Contextual[Unit] = log("initialize local " + sym.show + " with " + value.show, printer) {
     if sym.is(Flags.Mutable) then
       val addr = Heap.localVarAddr(summon[Regions.Data], sym, State.currentObject)
       Env.setLocalVar(sym, addr)
@@ -870,9 +872,6 @@ object Objects:
         case _ =>
           report.warning("[Internal error] Variable not found " + sym.show + "\nenv = " + env.show + ". Calling trace:\n" + Trace.show, Trace.position)
           Bottom
-      else if sym.isPatternBound then
-        // TODO: handle patterns
-        Cold
       else
         given Env.Data = env
         // Assume forward reference check is doing a good job
@@ -1113,11 +1112,9 @@ object Objects:
         else
           eval(arg, thisV, klass)
 
-      case Match(selector, cases) =>
-        eval(selector, thisV, klass)
-        // TODO: handle pattern match properly
-        report.warning("[initChecker] Pattern match is skipped. Trace:\n" + Trace.show, expr)
-        Bottom
+      case Match(scrutinee, cases) =>
+        val scrutineeValue = eval(scrutinee, thisV, klass)
+        patternMatch(scrutineeValue, cases, thisV, klass)
 
       case Return(expr, from) =>
         Returns.handle(from.symbol, eval(expr, thisV, klass))
@@ -1151,7 +1148,7 @@ object Objects:
         // local val definition
         val rhs = eval(vdef.rhs, thisV, klass)
         val sym = vdef.symbol
-        initLocal(thisV.asInstanceOf[Ref], vdef.symbol, rhs)
+        initLocal(vdef.symbol, rhs)
         Bottom
 
       case ddef : DefDef =>
@@ -1173,6 +1170,196 @@ object Objects:
         Bottom
   }
 
+  /** Evaluate the cases against the scrutinee value.
+   *
+   *  It returns the scrutinee in most cases. The main effect of the function is for its side effects of adding bindings
+   *  to the environment.
+   *
+   *  See https://docs.scala-lang.org/scala3/reference/changed-features/pattern-matching.html
+   *
+   *  @param scrutinee   The abstract value of the scrutinee.
+   *  @param cases       The cases to match.
+   *  @param thisV       The value for `C.this` where `C` is represented by `klass`.
+   *  @param klass       The enclosing class where the type `tp` is located.
+   */
+  def patternMatch(scrutinee: Value, cases: List[CaseDef], thisV: Value, klass: ClassSymbol): Contextual[Value] =
+    // expected member types for `unapplySeq`
+    def lengthType = ExprType(defn.IntType)
+    def lengthCompareType = MethodType(List(defn.IntType), defn.IntType)
+    def applyType(elemTp: Type) = MethodType(List(defn.IntType), elemTp)
+    def dropType(elemTp: Type) = MethodType(List(defn.IntType), defn.CollectionSeqType.appliedTo(elemTp))
+    def toSeqType(elemTp: Type) = ExprType(defn.CollectionSeqType.appliedTo(elemTp))
+
+    def getMemberMethod(receiver: Type, name: TermName, tp: Type): Denotation =
+      receiver.member(name).suchThat(receiver.memberInfo(_) <:< tp)
+
+    def evalCase(caseDef: CaseDef): Value =
+      evalPattern(scrutinee, caseDef.pat)
+      eval(caseDef.guard, thisV, klass)
+      eval(caseDef.body, thisV, klass)
+
+    /** Abstract evaluation of patterns.
+     *
+     *  It augments the local environment for bound pattern variables. As symbols are globally
+     *  unique, we can put them in a single environment.
+     *
+     *  Currently, we assume all cases are reachable, thus all patterns are assumed to match.
+     */
+    def evalPattern(scrutinee: Value, pat: Tree): Value = log("match " + scrutinee.show + " against " + pat.show, printer, (_: Value).show):
+      val trace2 = Trace.trace.add(pat)
+      pat match
+      case Alternative(pats) =>
+        for pat <- pats do evalPattern(scrutinee, pat)
+        scrutinee
+
+      case bind @ Bind(_, pat) =>
+        val value = evalPattern(scrutinee, pat)
+        initLocal(bind.symbol, value)
+        scrutinee
+
+      case UnApply(fun, implicits, pats) =>
+        given Trace = trace2
+
+        val fun1 = funPart(fun)
+        val funRef = fun1.tpe.asInstanceOf[TermRef]
+        val unapplyResTp = funRef.widen.finalResultType
+
+        val receiver = fun1 match
+          case ident: Ident =>
+            evalType(funRef.prefix, thisV, klass)
+          case select: Select =>
+            eval(select.qualifier, thisV, klass)
+
+        val implicitValues = evalArgs(implicits.map(Arg.apply), thisV, klass)
+        // TODO: implicit values may appear before and/or after the scrutinee parameter.
+        val unapplyRes = call(receiver, funRef.symbol, TraceValue(scrutinee, summon[Trace]) :: implicitValues, funRef.prefix, superType = NoType, needResolve = true)
+
+        if fun.symbol.name == nme.unapplySeq then
+          var resultTp = unapplyResTp
+          var elemTp = unapplySeqTypeElemTp(resultTp)
+          var arity = productArity(resultTp, NoSourcePosition)
+          var needsGet = false
+          if (!elemTp.exists && arity <= 0) {
+            needsGet = true
+            resultTp = resultTp.select(nme.get).finalResultType
+            elemTp = unapplySeqTypeElemTp(resultTp.widen)
+            arity = productSelectorTypes(resultTp, NoSourcePosition).size
+          }
+
+          var resToMatch = unapplyRes
+
+          if needsGet then
+            // Get match
+            val isEmptyDenot = unapplyResTp.member(nme.isEmpty).suchThat(_.info.isParameterless)
+            call(unapplyRes, isEmptyDenot.symbol, Nil, unapplyResTp, superType = NoType, needResolve = true)
+
+            val getDenot = unapplyResTp.member(nme.get).suchThat(_.info.isParameterless)
+            resToMatch = call(unapplyRes, getDenot.symbol, Nil, unapplyResTp, superType = NoType, needResolve = true)
+          end if
+
+          if elemTp.exists then
+            // sequence match
+            evalSeqPatterns(resToMatch, resultTp, elemTp, pats)
+          else
+            // product sequence match
+            val selectors = productSelectors(resultTp)
+            assert(selectors.length <= pats.length)
+            selectors.init.zip(pats).map { (sel, pat) =>
+              val selectRes = call(resToMatch, sel, Nil, resultTp, superType = NoType, needResolve = true)
+              evalPattern(selectRes, pat)
+            }
+            val seqPats = pats.drop(selectors.length - 1)
+            val toSeqRes = call(resToMatch, selectors.last, Nil, resultTp, superType = NoType, needResolve = true)
+            val toSeqResTp = resultTp.memberInfo(selectors.last).finalResultType
+            evalSeqPatterns(toSeqRes, toSeqResTp, elemTp, seqPats)
+          end if
+
+        else
+          // distribute unapply to patterns
+          if isProductMatch(unapplyResTp, pats.length) then
+            // product match
+            val selectors = productSelectors(unapplyResTp)
+            assert(selectors.length == pats.length)
+            selectors.zip(pats).map { (sel, pat) =>
+              val selectRes = call(unapplyRes, sel, Nil, unapplyResTp, superType = NoType, needResolve = true)
+              evalPattern(selectRes, pat)
+            }
+          else if unapplyResTp <:< defn.BooleanType then
+            // Boolean extractor, do nothing
+            ()
+          else
+            // Get match
+            val isEmptyDenot = unapplyResTp.member(nme.isEmpty).suchThat(_.info.isParameterless)
+            call(unapplyRes, isEmptyDenot.symbol, Nil, unapplyResTp, superType = NoType, needResolve = true)
+
+            val getDenot = unapplyResTp.member(nme.get).suchThat(_.info.isParameterless)
+            val getRes = call(unapplyRes, getDenot.symbol, Nil, unapplyResTp, superType = NoType, needResolve = true)
+            if pats.length == 1 then
+              // single match
+              evalPattern(getRes, pats.head)
+            else
+              val getResTp = getDenot.info.finalResultType
+              val selectors = productSelectors(getResTp).take(pats.length)
+              selectors.zip(pats).map { (sel, pat) =>
+                val selectRes = call(unapplyRes, sel, Nil, getResTp, superType = NoType, needResolve = true)
+                evalPattern(selectRes, pat)
+              }
+            end if
+          end if
+        end if
+        scrutinee
+
+      case Ident(nme.WILDCARD) | Ident(nme.WILDCARD_STAR) =>
+        scrutinee
+
+      case Typed(pat, _) =>
+        evalPattern(scrutinee, pat)
+
+      case tree =>
+        // For all other trees, the semantics is normal.
+        eval(tree, thisV, klass)
+
+    end evalPattern
+
+    /**
+     * Evaluate a sequence value against sequence patterns.
+     */
+    def evalSeqPatterns(scrutinee: Value, scrutineeType: Type, elemType: Type, pats: List[Tree])(using Trace): Unit =
+      // call .lengthCompare or .length
+      val lengthCompareDenot = getMemberMethod(scrutineeType, nme.lengthCompare, lengthCompareType)
+      if lengthCompareDenot.exists then
+        call(scrutinee, lengthCompareDenot.symbol, TraceValue(Bottom, summon[Trace]) :: Nil, scrutineeType, superType = NoType, needResolve = true)
+      else
+        val lengthDenot = getMemberMethod(scrutineeType, nme.length, lengthType)
+        call(scrutinee, lengthDenot.symbol, Nil, scrutineeType, superType = NoType, needResolve = true)
+      end if
+
+      // call .apply
+      val applyDenot = getMemberMethod(scrutineeType, nme.apply, applyType(elemType))
+      val applyRes = call(scrutinee, applyDenot.symbol, TraceValue(Bottom, summon[Trace]) :: Nil, scrutineeType, superType = NoType, needResolve = true)
+
+      if isWildcardStarArg(pats.last) then
+        if pats.size == 1 then
+          // call .toSeq
+          val toSeqDenot = scrutineeType.member(nme.toSeq).suchThat(_.info.isParameterless)
+          val toSeqRes = call(scrutinee, toSeqDenot.symbol, Nil, scrutineeType, superType = NoType, needResolve = true)
+          evalPattern(toSeqRes, pats.head)
+        else
+          // call .drop
+          val dropDenot = getMemberMethod(scrutineeType, nme.drop, applyType(elemType))
+          val dropRes = call(scrutinee, dropDenot.symbol, TraceValue(Bottom, summon[Trace]) :: Nil, scrutineeType, superType = NoType, needResolve = true)
+          for pat <- pats.init do evalPattern(applyRes, pat)
+          evalPattern(dropRes, pats.last)
+        end if
+      else
+        // no patterns like `xs*`
+      for pat <- pats do evalPattern(applyRes, pat)
+    end evalSeqPatterns
+
+
+    cases.map(evalCase).join
+  end patternMatch
+
   /** Handle semantics of leaf nodes
    *
    * For leaf nodes, their semantics is determined by their types.
@@ -1231,7 +1418,7 @@ object Objects:
           resolveThis(tref.classSymbol.asClass, thisV, klass)
 
       case _ =>
-        throw new Exception("unexpected type: " + tp)
+        throw new Exception("unexpected type: " + tp + ", Trace:\n" + Trace.show)
   }
 
   /** Evaluate arguments of methods and constructors */

compiler/src/dotty/tools/dotc/transform/init/Trace.scala

@@ -49,7 +49,12 @@ object Trace:
           val code = SyntaxHighlighting.highlight(pos.lineContent.trim.nn)
           i"$code\t$loc"
         else
-          tree.show
+          tree match
+            case defDef: DefTree =>
+              // The definition can be huge, avoid printing the whole definition.
+              defDef.symbol.show
+            case _ =>
+              tree.show
       val positionMarkerLine =
         if pos.exists && pos.source.exists then
           positionMarker(pos)

compiler/src/dotty/tools/dotc/transform/init/Util.scala

@@ -26,6 +26,9 @@ object Util:
   opaque type Arg  = Tree | ByNameArg
   case class ByNameArg(tree: Tree)
 
+  object Arg:
+    def apply(tree: Tree): Arg = tree
+
   extension (arg: Arg)
     def isByName = arg.isInstanceOf[ByNameArg]
     def tree: Tree = arg match

tests/init-global/neg/global-cycle1.check

@@ -1,17 +1,15 @@
 -- Error: tests/init-global/neg/global-cycle1.scala:1:7 ----------------------------------------------------------------
 1 |object A {             // error
-  |^
-  |Cyclic initialization: object A -> object B -> object A. Calling trace:
-  |-> object A {             // error	[ global-cycle1.scala:1 ]
-  |   ^
-  |-> val a: Int = B.b	[ global-cycle1.scala:2 ]
-  |                ^
-  |-> object B {	[ global-cycle1.scala:5 ]
-  |   ^
-  |-> val b: Int = A.a     // error	[ global-cycle1.scala:6 ]
-  |                ^
-2 |  val a: Int = B.b
-3 |}
+  |       ^
+  |       Cyclic initialization: object A -> object B -> object A. Calling trace:
+  |       -> object A {             // error	[ global-cycle1.scala:1 ]
+  |          ^
+  |       -> val a: Int = B.b	[ global-cycle1.scala:2 ]
+  |                       ^
+  |       -> object B {	[ global-cycle1.scala:5 ]
+  |          ^
+  |       -> val b: Int = A.a     // error	[ global-cycle1.scala:6 ]
+  |                       ^
 -- Error: tests/init-global/neg/global-cycle1.scala:6:17 ---------------------------------------------------------------
 6 |  val b: Int = A.a     // error
   |               ^^^

tests/init-global/neg/global-cycle6.scala

@@ -1,7 +1,7 @@
 object A {             // error
   val n: Int = B.m
   class Inner {
-    println(n)
+    println(n)         // error
   }
 }
 

tests/init-global/neg/patmat-unapplySeq.check

@@ -0,0 +1,11 @@
+-- Error: tests/init-global/neg/patmat-unapplySeq.scala:8:32 -----------------------------------------------------------
+8 |  def apply(i: Int): Box = array(i)             // error
+  |                           ^^^^^^^^
+  |Reading mutable state of object A during initialization of object B.
+  |Reading mutable state of other static objects is forbidden as it breaks initialization-time irrelevance. Calling trace: 
+  |-> object B:	[ patmat-unapplySeq.scala:15 ]
+  |   ^
+  |-> case A(b) =>	[ patmat-unapplySeq.scala:17 ]
+  |        ^^^^
+  |-> def apply(i: Int): Box = array(i)             // error	[ patmat-unapplySeq.scala:8 ]
+  |                            ^^^^^^^^

tests/init-global/neg/patmat-unapplySeq.scala

@@ -0,0 +1,17 @@
+object A:
+  class Box(var x: Int)
+
+  val array: Array[Box] = new Array(1)
+  array(0) = new Box(10)
+
+  def length: Int = array.length
+  def apply(i: Int): Box = array(i)             // error
+  def drop(n: Int): Seq[Box] = array.toSeq
+  def toSeq: Seq[Box] = array.toSeq
+
+  def unapplySeq(array: Array[Box]): A.type = this
+
+
+object B:
+  A.array match
+  case A(b) =>

tests/init-global/neg/patmat-unapplySeq2.scala

@@ -0,0 +1,17 @@
+object A:
+  class Box(var x: Int)
+
+  val array: Array[Box] = new Array(1)
+  array(0) = new Box(10)
+
+  def length: Int = array.length
+  def apply(i: Int): Box = array(i)             // error
+  def drop(n: Int): Seq[Box] = array.toSeq
+  def toSeq: Seq[Box] = array.toSeq
+
+  def unapplySeq(array: Array[Box]): A.type = this
+
+
+object B:
+  A.array match
+  case A(b*) =>