Push a decl name scope before calling `CalleePatternMatch()` (#5771)

Otherwise the return values of different functions collide.

Part of #5063.

toolchain/check/import_cpp.cpp

@@ -697,10 +697,12 @@ static auto CreateFunctionParamsInsts(Context& context, SemIR::LocId loc_id,
   if (SemIR::ErrorInst::InstId == return_slot_pattern_id) {
     return std::nullopt;
   }
+
   // TODO: Add support for implicit parameters.
   auto call_params_id = CalleePatternMatch(
       context, /*implicit_param_patterns_id=*/SemIR::InstBlockId::None,
       param_patterns_id, return_slot_pattern_id);
+
   return {{.param_patterns_id = param_patterns_id,
            .return_slot_pattern_id = return_slot_pattern_id,
            .call_params_id = call_params_id}};
@@ -726,6 +728,7 @@ static auto ImportFunctionDecl(Context& context, SemIR::LocId loc_id,
     return SemIR::ErrorInst::InstId;
   }
 
+  context.scope_stack().PushForDeclName();
   context.inst_block_stack().Push();
   context.pattern_block_stack().Push();
 
@@ -734,6 +737,7 @@ static auto ImportFunctionDecl(Context& context, SemIR::LocId loc_id,
 
   auto pattern_block_id = context.pattern_block_stack().Pop();
   auto decl_block_id = context.inst_block_stack().Pop();
+  context.scope_stack().Pop();
 
   if (!function_params_insts.has_value()) {
     return SemIR::ErrorInst::InstId;

toolchain/check/testdata/interop/cpp/function/return.carbon

@@ -52,6 +52,31 @@ fn F() {
   //@dump-sem-ir-end
 }
 
+// ============================================================================
+// Multiple function with a return value
+// ============================================================================
+
+// --- multiple.h
+
+auto foo1() -> short;
+auto foo2() -> int;
+
+// --- import_multiple.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "multiple.h";
+
+fn IngestI16(x: i16);
+fn IngestI32(x: i32);
+
+fn F() {
+  //@dump-sem-ir-begin
+  IngestI16(Cpp.foo1());
+  IngestI32(Cpp.foo2());
+  //@dump-sem-ir-end
+}
+
 // ============================================================================
 // float
 // ============================================================================
@@ -155,6 +180,61 @@ fn F() {
 // CHECK:STDOUT:   <elided>
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
+// CHECK:STDOUT: --- import_multiple.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %int_16: Core.IntLiteral = int_value 16 [concrete]
+// CHECK:STDOUT:   %empty_tuple.type: type = tuple_type () [concrete]
+// CHECK:STDOUT:   %i16: type = class_type @Int, @Int(%int_16) [concrete]
+// CHECK:STDOUT:   %IngestI16.type: type = fn_type @IngestI16 [concrete]
+// CHECK:STDOUT:   %IngestI16: %IngestI16.type = struct_value () [concrete]
+// CHECK:STDOUT:   %int_32: Core.IntLiteral = int_value 32 [concrete]
+// CHECK:STDOUT:   %i32: type = class_type @Int, @Int(%int_32) [concrete]
+// CHECK:STDOUT:   %IngestI32.type: type = fn_type @IngestI32 [concrete]
+// CHECK:STDOUT:   %IngestI32: %IngestI32.type = struct_value () [concrete]
+// CHECK:STDOUT:   %foo1.type: type = fn_type @foo1 [concrete]
+// CHECK:STDOUT:   %foo1: %foo1.type = struct_value () [concrete]
+// CHECK:STDOUT:   %foo2.type: type = fn_type @foo2 [concrete]
+// CHECK:STDOUT:   %foo2: %foo2.type = struct_value () [concrete]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
+// CHECK:STDOUT:     .foo1 = %foo1.decl
+// CHECK:STDOUT:     .foo2 = %foo2.decl
+// CHECK:STDOUT:     import Cpp//...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %foo1.decl: %foo1.type = fn_decl @foo1 [concrete = constants.%foo1] {
+// CHECK:STDOUT:     <elided>
+// CHECK:STDOUT:   } {
+// CHECK:STDOUT:     <elided>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %foo2.decl: %foo2.type = fn_decl @foo2 [concrete = constants.%foo2] {
+// CHECK:STDOUT:     <elided>
+// CHECK:STDOUT:   } {
+// CHECK:STDOUT:     <elided>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @F() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %IngestI16.ref: %IngestI16.type = name_ref IngestI16, file.%IngestI16.decl [concrete = constants.%IngestI16]
+// CHECK:STDOUT:   %Cpp.ref.loc11: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   %foo1.ref: %foo1.type = name_ref foo1, imports.%foo1.decl [concrete = constants.%foo1]
+// CHECK:STDOUT:   %foo1.call: init %i16 = call %foo1.ref()
+// CHECK:STDOUT:   %.loc11_22.1: %i16 = value_of_initializer %foo1.call
+// CHECK:STDOUT:   %.loc11_22.2: %i16 = converted %foo1.call, %.loc11_22.1
+// CHECK:STDOUT:   %IngestI16.call: init %empty_tuple.type = call %IngestI16.ref(%.loc11_22.2)
+// CHECK:STDOUT:   %IngestI32.ref: %IngestI32.type = name_ref IngestI32, file.%IngestI32.decl [concrete = constants.%IngestI32]
+// CHECK:STDOUT:   %Cpp.ref.loc12: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   %foo2.ref: %foo2.type = name_ref foo2, imports.%foo2.decl [concrete = constants.%foo2]
+// CHECK:STDOUT:   %foo2.call: init %i32 = call %foo2.ref()
+// CHECK:STDOUT:   %.loc12_22.1: %i32 = value_of_initializer %foo2.call
+// CHECK:STDOUT:   %.loc12_22.2: %i32 = converted %foo2.call, %.loc12_22.1
+// CHECK:STDOUT:   %IngestI32.call: init %empty_tuple.type = call %IngestI32.ref(%.loc12_22.2)
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
 // CHECK:STDOUT: --- fail_todo_import_float.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {