Sema: Minor adjustment to BindingSet dumping

Shorten some of the keys and format them consistently as sentence
fragments rather than identifiers.

Author: AnthonyLatsis

docs/DebuggingTheCompiler.md

@@ -173,13 +173,13 @@ constraints and present the final type checked solution, e.g.:
 
 Score: <default 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0>
 Type Variables:
-   ($T0 [attributes: [literal: integer]] [with possible bindings: (default type of literal) Int]) @ locator@0x13e009800 [[email protected]:3:1]
+   ($T0 [attributes: [literal: integer]] [potential bindings: (default type of literal) Int]) @ locator@0x13e009800 [[email protected]:3:1]
 
 Inactive Constraints:
   $T0 literal conforms to ExpressibleByIntegerLiteral @ locator@0x13e009800 [[email protected]:3:1]
 
   (Potential Binding(s): 
-    ($T0 [attributes: [literal: integer]] [with possible bindings: (default type of literal) Int])
+    ($T0 [attributes: [literal: integer]] [potential bindings: (default type of literal) Int])
   (attempting type variable $T0 := Int
     (considering: $T0 literal conforms to ExpressibleByIntegerLiteral @ locator@0x13e009800 [[email protected]:3:1]
       (simplification result:

lib/Sema/CSBindings.cpp

@@ -2196,16 +2196,27 @@ void BindingSet::dump(llvm::raw_ostream &out, unsigned indent) const {
     out << "] ";
 
   if (involvesTypeVariables()) {
-    out << "[involves_type_vars: ";
-    interleave(AdjacentVars,
-               [&](const auto *typeVar) { out << typeVar->getString(PO); },
-               [&out]() { out << ", "; });
+    out << "[adjacent to: ";
+    if (AdjacentVars.empty()) {
+      out << "<none>";
+    } else {
+      SmallVector<TypeVariableType *> adjacentVars(AdjacentVars.begin(),
+                                                   AdjacentVars.end());
+      llvm::sort(adjacentVars,
+                 [](const TypeVariableType *lhs, const TypeVariableType *rhs) {
+                   return lhs->getID() < rhs->getID();
+                 });
+      interleave(
+          adjacentVars,
+          [&](const auto *typeVar) { out << typeVar->getString(PO); },
+          [&out]() { out << ", "; });
+    }
     out << "] ";
   }
 
   auto numDefaultable = getNumViableDefaultableBindings();
   if (numDefaultable > 0)
-    out << "[#defaultable_bindings: " << numDefaultable << "] ";
+    out << "[defaultable bindings: " << numDefaultable << "] ";
 
   struct PrintableBinding {
   private:
@@ -2251,7 +2262,7 @@ void BindingSet::dump(llvm::raw_ostream &out, unsigned indent) const {
     }
   };
 
-  out << "[with possible bindings: ";
+  out << "[potential bindings: ";
   SmallVector<PrintableBinding, 2> potentialBindings;
   for (const auto &binding : Bindings) {
     switch (binding.Kind) {
@@ -2275,7 +2286,7 @@ void BindingSet::dump(llvm::raw_ostream &out, unsigned indent) const {
     }
   }
   if (potentialBindings.empty()) {
-    out << "<empty>";
+    out << "<none>";
   } else {
     interleave(
         potentialBindings,

lib/Sema/TypeCheckConstraints.cpp

@@ -75,7 +75,7 @@ void TypeVariableType::Implementation::print(llvm::raw_ostream &OS) {
   if (isPackExpansion())
     bindingOptions.push_back(TypeVariableOptions::TVO_PackExpansion);
   if (!bindingOptions.empty()) {
-    OS << " [allows bindings to: ";
+    OS << " [can bind to: ";
     interleave(bindingOptions, OS,
                [&](TypeVariableOptions option) {
                   (OS << getTypeVariableOptions(option));},

unittests/Sema/CMakeLists.txt

@@ -4,6 +4,7 @@ add_swift_unittest(swiftSemaTests
   BindingInferenceTests.cpp
   ConstraintGenerationTests.cpp
   ConstraintSimplificationTests.cpp
+  ConstraintSystemDumpTests.cpp
   UnresolvedMemberLookupTests.cpp
   PlaceholderTypeInferenceTests.cpp
   SolutionFilteringTests.cpp

unittests/Sema/ConstraintSystemDumpTests.cpp

@@ -0,0 +1,70 @@
+//===--- ConstraintSystemDumpTests.cpp ------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include "SemaFixture.h"
+#include "swift/Sema/ConstraintSystem.h"
+
+using namespace swift;
+using namespace swift::unittest;
+
+TEST_F(SemaTest, DumpConstraintSystemBasic) {
+  ConstraintSystemOptions options;
+  ConstraintSystem cs(DC, options);
+
+  auto *emptyLoc = cs.getConstraintLocator({});
+
+  auto *t0 = cs.createTypeVariable(emptyLoc, TVO_CanBindToLValue);
+  auto *t1 = cs.createTypeVariable(emptyLoc, 0);
+  auto *t2 = cs.createTypeVariable(
+      cs.getConstraintLocator(emptyLoc, ConstraintLocator::GenericArgument),
+      TVO_CanBindToHole | TVO_CanBindToPack);
+
+  cs.addUnsolvedConstraint(Constraint::create(
+      cs, ConstraintKind::Bind, t2,
+      TupleType::get({Type(t0), Type(t1)}, Context), emptyLoc));
+
+  std::string expectedOutput =
+      R"(Score: <default 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0>
+Type Variables:
+  $T0 [can bind to: lvalue] [adjacent to: $T1, $T2] [potential bindings: <none>] @ locator@ []
+  $T1 [adjacent to: $T0, $T2] [potential bindings: <none>] @ locator@ []
+  $T2 [can bind to: hole, pack] [potential bindings: <none>] @ locator@ [ → generic argument #0]
+Inactive Constraints:
+  $T2 bind ($T0, $T1) @ locator@ []
+)";
+
+  std::string actualOutput;
+  {
+    llvm::raw_string_ostream os(actualOutput);
+    cs.print(os);
+
+    // Remove locator addresses.
+    std::string adjustedOutput;
+    const auto size = actualOutput.size();
+    size_t pos = 0;
+    while (pos < size) {
+      auto addr_pos = actualOutput.find("0x", pos);
+      if (addr_pos == std::string::npos) {
+        adjustedOutput += actualOutput.substr(pos, std::string::npos);
+        break;
+      } else {
+        adjustedOutput += actualOutput.substr(pos, addr_pos - pos);
+      }
+
+      pos = actualOutput.find(' ', addr_pos);
+    }
+
+    actualOutput = adjustedOutput;
+  }
+
+  EXPECT_EQ(expectedOutput, actualOutput);
+}