From 790e075986acb74ad78cb28844b8a99e3c5cf969 Mon Sep 17 00:00:00 2001
From: Thejaswi Kadur <tkadur@users.noreply.github.com>
Date: Wed, 27 Jul 2022 10:29:09 -0700
Subject: [PATCH] Convert first Print argument to String before evaluating
 (#1548)

Fixes #1439.
---
 explorer/interpreter/interpreter.cpp          | 13 +++++----
 .../testdata/print/associated_constant.carbon | 27 +++++++++++++++++++
 2 files changed, 35 insertions(+), 5 deletions(-)
 create mode 100644 explorer/testdata/print/associated_constant.carbon

diff --git a/explorer/interpreter/interpreter.cpp b/explorer/interpreter/interpreter.cpp
index a8c362887be0..770a67adae13 100644
--- a/explorer/interpreter/interpreter.cpp
+++ b/explorer/interpreter/interpreter.cpp
@@ -1156,15 +1156,18 @@ auto Interpreter::StepExp() -> ErrorOr<Success> {
       switch (cast<IntrinsicExpression>(exp).intrinsic()) {
         case IntrinsicExpression::Intrinsic::Print: {
           const auto& args = cast<TupleValue>(*act.results()[0]).elements();
+          CARBON_ASSIGN_OR_RETURN(
+              Nonnull<const Value*> format_string_value,
+              Convert(args[0], arena_->New<StringType>(), exp.source_loc()));
+          const char* format_string =
+              cast<StringValue>(*format_string_value).value().c_str();
           switch (args.size()) {
             case 1:
-              llvm::outs() << llvm::formatv(
-                  cast<StringValue>(*args[0]).value().c_str());
+              llvm::outs() << llvm::formatv(format_string);
               break;
             case 2:
-              llvm::outs() << llvm::formatv(
-                  cast<StringValue>(*args[0]).value().c_str(),
-                  cast<IntValue>(*args[1]).value());
+              llvm::outs() << llvm::formatv(format_string,
+                                            cast<IntValue>(*args[1]).value());
               break;
             default:
               CARBON_FATAL() << "Unexpected arg count: " << args.size();
diff --git a/explorer/testdata/print/associated_constant.carbon b/explorer/testdata/print/associated_constant.carbon
new file mode 100644
index 000000000000..7d2836f61716
--- /dev/null
+++ b/explorer/testdata/print/associated_constant.carbon
@@ -0,0 +1,27 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// RUN: %{explorer} %s 2>&1 | \
+// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
+// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
+// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// AUTOUPDATE: %{explorer} %s
+// CHECK: i32
+// CHECK: String
+// CHECK: result: 0
+
+package Testcase api;
+
+interface HasName {
+    let Name:! String;
+}
+
+external impl i32 as HasName where .Name == "i32" {}
+external impl String as HasName where .Name == "String" {}
+
+fn Main() -> i32 {
+    Print(i32.(HasName.Name));
+    Print(String.(HasName.Name));
+    return 0;
+}