test runner: build dshell harness with compiler under test

The dshell prebuilt library and per-test driver were built with the host
compiler (e.g. LDC 1.23 on the VisualD CI), which is too old to parse the
current druntime/Phobos sources (short '=>' function bodies etc.), causing
parse errors when their imports were analyzed. They also import Phobos and
link against each other, so build both with the compiler under test using
PHOBOS_DFLAGS instead, matching the pre-druntime-only behaviour.

Also strip the benign LNK4255 'multiple objects of the same name' linker
warning: druntime.lib is built as one 'dmd -lib' archive and contains
several objects sharing a basename (memory.obj etc.), so the MS linker
warns when linking with -g, leaking into tests that expect no output.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: dkorpel

compiler/test/run.d

@@ -337,15 +337,23 @@ void ensureToolsExists(const string[string] env, const TestTool[] tools ...)
         }
 
         string[] buildCommand;
+        string[string] buildEnv = null;
         if (tool.linksWithTests)
         {
+            // The dshell library imports Phobos and is linked against the tests,
+            // so it must be built by the compiler under test (the host compiler
+            // may be too old to parse the current druntime/Phobos) using the
+            // Phobos DFLAGS rather than the druntime-only default.
             buildCommand = [
-                hostDMD,
+                env["DMD"],
+                "-conf=",
                 "-m"~env["MODEL"],
                 "-of" ~ targetBin,
                 "-c",
                 sourceFile
             ] ~ getPicFlags(env);
+            buildEnv = env.dup;
+            buildEnv["DFLAGS"] = env.get("PHOBOS_DFLAGS", "");
         }
         else
         {
@@ -359,7 +367,7 @@ void ensureToolsExists(const string[string] env, const TestTool[] tools ...)
 
         writefln("Executing: %-(%s %)", buildCommand);
         stdout.flush();
-        if (spawnProcess(buildCommand, null).wait)
+        if (spawnProcess(buildCommand, buildEnv).wait)
         {
             stderr.writefln("failed to build '%s'", targetBin);
             atomicOp!"+="(failCount, 1);

compiler/test/tools/d_do_test.d

@@ -1845,6 +1845,12 @@ int tryMain(string[] args)
 
                 compile_output = compile_output.unifyNewLine();
                 compile_output = std.regex.replaceAll(compile_output, regex(`^DMD v2\.[0-9]+.*\n? DEBUG$`, "m"), "");
+                // druntime.lib is built as a single library with `dmd -lib`, so
+                // it contains several object files with the same basename (e.g.
+                // memory.obj from core.memory and rt.memory). The MS linker emits
+                // a benign LNK4255 warning about this when linking with `-g`;
+                // strip it so it doesn't fail tests that expect no output.
+                compile_output = std.regex.replaceAll(compile_output, regex(`^.*warning LNK4255:.*\n?`, "m"), "");
                 compile_output = std.string.strip(compile_output);
                 // replace test_result path with fixed ones
                 compile_output = compile_output.replace(result_path, resultsDirReplacement);
@@ -2355,15 +2361,18 @@ static this()
     auto outfile = File(output_file, "w");
     enum keepFilesOpen = Config.retainStdout | Config.retainStderr;
 
-    // dshell scripts are test-harness code that should not be driven by the
-    // compiler under test, but by a stable host compiler.
+    // dshell scripts import Phobos (std.process etc.) and link against the
+    // prebuilt dshell library, so build them with the compiler under test and
+    // the Phobos DFLAGS: the host compiler may be too old to parse the current
+    // druntime/Phobos sources, and the prebuilt library is built by the
+    // compiler under test too, so both must agree.
     environment["DFLAGS"] = envData.phobosDflags;
 
     //
     // compile the test
     //
     {
-        const compile = [envData.hostDmd, "-m"~envData.model] ~
+        const compile = [envData.dmd, "-conf=", "-m"~envData.model] ~
             envData.picFlag ~ [
             "-od" ~ testOutDir,
             "-of" ~ testScriptExe,
@@ -2377,13 +2386,9 @@ static this()
         ];
         outfile.writeln("[COMPILE_TEST] ", escapeShellCommand(compile));
         outfile.flush();
-        // Build with the host compiler's own configuration: clear DFLAGS so the
-        // druntime-only flags (and the Phobos PHOBOS_DFLAGS) don't leak in here.
-        auto compileEnv = environment.toAA();
-        compileEnv.remove("DFLAGS");
         // Note that spawnprocess closes the file, so it will need to be re-opened
         // below when we run the test
-        auto compileProc = std.process.spawnProcess(compile, stdin, outfile, outfile, compileEnv, keepFilesOpen);
+        auto compileProc = std.process.spawnProcess(compile, stdin, outfile, outfile, null, keepFilesOpen);
         const exitCode = wait(compileProc);
         if (exitCode != 0)
         {