[clang] [clang][driver] Don't emit an error on an unrecognized SDK name (PR #181897)

[Ian Anderson via cfe-commits]

https://github.com/ian-twilightcoder created https://github.com/llvm/llvm-project/pull/181897

-isysroot can be an unrecognized value in unusual circumstances. Don't emit an error when checking the triple against such an isysroot, let the user try to do what they're trying to do.

>From 02d733809b0a1ca95a832c888bd51d1bd40764aa Mon Sep 17 00:00:00 2001
From: Ian Anderson <iana at apple.com>
Date: Tue, 17 Feb 2026 12:10:56 -0800
Subject: [PATCH] [clang][driver] Don't emit an error on an unrecognized SDK
 name

-isysroot can be an unrecognized value in unusual circumstances. Don't emit an error when checking the triple against such an isysroot, let the user try to do what they're trying to do.
---
 clang/lib/Driver/ToolChains/Darwin.cpp              | 13 ++++++-------
 .../XRSimulator1.0.sdk/usr/include/libxml/.keep     |  0
 clang/test/Driver/incompatible_sysroot.c            |  1 +
 3 files changed, 7 insertions(+), 7 deletions(-)
 create mode 100644 clang/test/Driver/Inputs/XRSimulator1.0.sdk/usr/include/libxml/.keep

diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
index 1c95a79a52a9c..0650b49017290 100644
--- a/clang/lib/Driver/ToolChains/Darwin.cpp
+++ b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -1145,11 +1145,11 @@ void Darwin::VerifyTripleForSDK(const llvm::opt::ArgList &Args,
       getDriver().Diag(diag::warn_incompatible_sysroot)
           << SDKInfo->getDisplayName() << Triple.getTriple();
   } else if (const Arg *A = Args.getLastArg(options::OPT_isysroot)) {
+    // If there is no SDK info, assume this is building against an SDK that
+    // predates SDKSettings.json. Try to match the triple to the SDK path.
     const char *isysroot = A->getValue();
-    StringRef SDK = getSDKName(isysroot);
-    if (!SDK.empty()) {
-      size_t StartVer = SDK.find_first_of("0123456789");
-      StringRef SDKName = SDK.slice(0, StartVer);
+    StringRef SDKName = getSDKName(isysroot);
+    if (!SDKName.empty()) {
       bool supported = true;
       if (Triple.isWatchOS())
         supported = SDKName.starts_with("Watch");
@@ -1161,9 +1161,8 @@ void Darwin::VerifyTripleForSDK(const llvm::opt::ArgList &Args,
         supported = SDKName.starts_with("iPhone");
       else if (Triple.isMacOSX())
         supported = SDKName.starts_with("MacOSX");
-      else
-        llvm::reportFatalUsageError(Twine("SDK at '") + isysroot +
-                                    "' missing SDKSettings.json.");
+      // If it's not an older SDK, then it might be a damaged SDK or a
+      // non-standard -isysroot path. Don't try to diagnose that here.
 
       if (!supported)
         getDriver().Diag(diag::warn_incompatible_sysroot)
diff --git a/clang/test/Driver/Inputs/XRSimulator1.0.sdk/usr/include/libxml/.keep b/clang/test/Driver/Inputs/XRSimulator1.0.sdk/usr/include/libxml/.keep
new file mode 100644
index 0000000000000..e69de29bb2d1d
diff --git a/clang/test/Driver/incompatible_sysroot.c b/clang/test/Driver/incompatible_sysroot.c
index a5f7d03da7254..ee88d241a3496 100644
--- a/clang/test/Driver/incompatible_sysroot.c
+++ b/clang/test/Driver/incompatible_sysroot.c
@@ -12,6 +12,7 @@
 // RUN: %clang -target arm64-apple-visionos1.0-simulator -Wincompatible-sysroot -isysroot %S/Inputs/XRSimulator1.0.sdk -S -o - %s 2>&1 | FileCheck -check-prefix CHECK-VISIONOSSIM %s
 // RUN: %clang -target arm64-apple-xros1.0 -Wincompatible-sysroot -isysroot %S/Inputs/XRSimulator1.0.sdk -S -o - %s 2>&1 | FileCheck -check-prefix CHECK-VISIONOSSIM-VISIONOS %s
 // RUN: %clang -target arm64-apple-ios17.1 -Wincompatible-sysroot -isysroot %S/Inputs/XRSimulator1.0.sdk -S -o - %s 2>&1 | FileCheck -check-prefix CHECK-VISIONOSSIM-IOS %s
+// RUN: %clang -target arm64-apple-visionos1.0-simulator -Wincompatible-sysroot -isysroot %S/Inputs/XRSimulator1.0.sdk/usr/include/libxml -S -o - %s 2>&1 | FileCheck -check-prefix CHECK-VISIONOSSIM %s
 
 int main() { return 0; }
 // CHECK-OSX-IOS: warning: using sysroot for 'MacOSX' but targeting 'x86_64-apple-ios9.0.0-simulator'