[CodeComplete] Complete argument labels in generic initializer

The actual fix is to perform qualified lookup on a TypeExpr in `collectPossibleCalleesForApply`.

This changes the behaviour of some test cases in `complete_multiple_trailingclosure.swift`, which now provide argument labels. To make the choices suggested less verbose, I refined the parameter matching to only match trailing closures to parameters of function types.

In `INIT_FALLBACK_1` we technically shouldn't be suggesting `arg3` based on the matched argument types (the closure returns `Int` and the constructor with `arg3` requires the closure to return `String`), but AFAICT we aren't doing type-checking at this stage, so there's no way to rule it out.

Author: ahoppen

lib/IDE/ExprContextAnalysis.cpp

@@ -653,6 +653,9 @@ static bool collectPossibleCalleesForApply(
   } else if (auto CRCE = dyn_cast<ConstructorRefCallExpr>(fnExpr)) {
     collectPossibleCalleesByQualifiedLookup(
         DC, CRCE->getArg(), DeclNameRef::createConstructor(), candidates);
+  } else if (auto TE = dyn_cast<TypeExpr>(fnExpr)) {
+    collectPossibleCalleesByQualifiedLookup(
+        DC, TE, DeclNameRef::createConstructor(), candidates);
   } else if (auto *UME = dyn_cast<UnresolvedMemberExpr>(fnExpr)) {
     collectPossibleCalleesForUnresolvedMember(DC, UME, candidates);
   }
@@ -806,23 +809,37 @@ static bool getPositionInParams(DeclContext &DC, Expr *Args, Expr *CCExpr,
     }
 
     // Look for a matching parameter label.
-    bool FoundLabelMatch = false;
+    bool AdvancedPosInParams = false;
     for (unsigned i = PosInParams; i < Params.size(); ++i) {
       if (Params[i].getLabel() == ArgName) {
         // We have found a label match. Advance the position in the params
         // to point to the param after the one with this label.
         PosInParams = i + 1;
-        FoundLabelMatch = true;
+        AdvancedPosInParams = true;
         if (Params[i].isVariadic()) {
           LastParamWasVariadic = true;
         }
         break;
       }
     }
 
-    if (!FoundLabelMatch) {
-      // We haven't found a matching argument label. Assume the current one is
-      // named incorrectly and advance by one.
+    bool IsTrailingClosure =
+        PosInArgs >= tuple->getNumElements() - tuple->getNumTrailingElements();
+    if (!AdvancedPosInParams && IsTrailingClosure) {
+      // If the argument is a trailing closure, it can't match non-function
+      // parameters. Advance to the next function parameter.
+      for (unsigned i = PosInParams; i < Params.size(); ++i) {
+        if (Params[i].getParameterType()->is<FunctionType>()) {
+          PosInParams = i + 1;
+          AdvancedPosInParams = true;
+          break;
+        }
+      }
+    }
+
+    if (!AdvancedPosInParams) {
+      // We haven't performed any special advance logic. Assume the argument
+      // and parameter match, so advance PosInParams by 1.
       ++PosInParams;
     }
   }

test/IDE/complete_call_arg.swift

@@ -888,3 +888,14 @@ func testCompleteLabelAfterVararg() {
     // COMPLETE_MEMBER_IN_VARARG: End completions
   }
 }
+
+func testGenericConstructor() {
+  public struct TextField<Label> {
+    init(label: String, text: String) {}
+  }
+
+  _ = TextField(label: "Encoded", #^GENERIC_INITIALIZER^#)
+// GENERIC_INITIALIZER: Begin completions, 1 item
+// GENERIC_INITIALIZER-DAG: Pattern/ExprSpecific:               {#text: String#}[#String#]
+// GENERIC_INITIALIZER: End completions
+}

test/IDE/complete_multiple_trailingclosure.swift

@@ -13,8 +13,8 @@
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=INIT_REQUIRED_NEWLINE_2 | %FileCheck %s -check-prefix=INIT_REQUIRED_NEWLINE_2
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=INIT_REQUIRED_SAMELINE_3 | %FileCheck %s -check-prefix=INIT_REQUIRED_SAMELINE_3
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=INIT_REQUIRED_NEWLINE_3 | %FileCheck %s -check-prefix=INIT_REQUIRED_NEWLINE_3
-// RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=INIT_FALLBACK_1 | %FileCheck %s -check-prefix=INIT_FALLBACK
-// RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=INIT_FALLBACK_2 | %FileCheck %s -check-prefix=INIT_FALLBACK
+// RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=INIT_FALLBACK_1 | %FileCheck %s -check-prefix=INIT_FALLBACK_1
+// RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=INIT_FALLBACK_2 | %FileCheck %s -check-prefix=INIT_FALLBACK_2
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=MEMBERDECL_SAMELINE | %FileCheck %s -check-prefix=MEMBERDECL_SAMELINE
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=MEMBERDECL_NEWLINE | %FileCheck %s -check-prefix=MEMBERDECL_NEWLINE
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=INITIALIZED_VARDECL_SAMELINE | %FileCheck %s -check-prefix=INITIALIZED_VARDECL_SAMELINE
@@ -201,15 +201,25 @@ func testFallbackPostfix() {
   let _ = MyStruct4 {
     1
   } #^INIT_FALLBACK_1^#
-// INIT_FALLBACK: Begin completions, 2 items
-// INIT_FALLBACK-DAG: Decl[InstanceMethod]/CurrNominal:   .testStructMethod()[#Void#];
-// INIT_FALLBACK-DAG: Keyword[self]/CurrNominal:          .self[#MyStruct4<Int>#];
-// INIT_FALLBACK: End completions
+// FIXME: We shouldn't be suggesting arg3 here because the second initializer
+// doesn't match the already-provided parameters (missing `name` label argument
+// and closure does not return `String`). However, we are not type-checking at
+// the stage at which we complete argument labels, so we can't rule it out for
+// now (SR-14450).
+// INIT_FALLBACK_1: Begin completions, 3 items
+// INIT_FALLBACK_1-DAG: Pattern/ExprSpecific:               {#arg3: () -> _ {|}#}[#() -> _#]
+// INIT_FALLBACK_1-DAG: Decl[InstanceMethod]/CurrNominal:   .testStructMethod()[#Void#];
+// INIT_FALLBACK_1-DAG: Keyword[self]/CurrNominal:          .self[#MyStruct4<Int>#];
+// INIT_FALLBACK_1: End completions
   let _ = MyStruct4(name: "test") {
     ""
   } arg3: {
     1
   } #^INIT_FALLBACK_2^#
+// INIT_FALLBACK_2: Begin completions, 2 items
+// INIT_FALLBACK_2-DAG: Decl[InstanceMethod]/CurrNominal:   .testStructMethod()[#Void#];
+// INIT_FALLBACK_2-DAG: Keyword[self]/CurrNominal:          .self[#MyStruct4<Int>#];
+// INIT_FALLBACK_2: End completions
 }
 
 protocol P {