Add support for sysroot-relative system header search paths

[etcwilde]

Clang supported header searchpaths of the form -I =/path, relative to the sysroot if one is passed, but did not implement that behavior for -iquote, -isystem, or -idirafter.

This implements the = portion of the behavior implemented by GCC for these flags described in https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Evan Wilde (etcwilde)

Changes

Clang supported header searchpaths of the form -I =/path, relative to the sysroot if one is passed, but did not implement that behavior for -iquote, -isystem, or -idirafter.

This implements the = portion of the behavior implemented by GCC for these flags described in https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html.

---

Full diff: https://github.com/llvm/llvm-project/pull/82084.diff

2 Files Affected:

• (modified) clang/lib/Frontend/CompilerInvocation.cpp (+22-14)
• (modified) clang/test/Preprocessor/sysroot-prefix.c (+14)

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index bcb31243056b7e..4b5667f6ae5a5d 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -3218,6 +3218,21 @@ static bool ParseHeaderSearchArgs(HeaderSearchOptions &Opts, ArgList &Args,
   bool IsIndexHeaderMap = false;
   bool IsSysrootSpecified =
       Args.hasArg(OPT__sysroot_EQ) || Args.hasArg(OPT_isysroot);
+
+  // Expand a leading `=` to the sysroot if one was passed (and it's not a
+  // framework flag).
+  auto ConvertHeaderPath = [IsSysrootSpecified,
+                            &Opts](const llvm::opt::Arg *A,
+                                   bool IsFramework = false) -> std::string {
+    if (IsSysrootSpecified && !IsFramework && A->getValue()[0] == '=') {
+      SmallString<32> Buffer;
+      llvm::sys::path::append(Buffer, Opts.Sysroot,
+                              llvm::StringRef(A->getValue()).substr(1));
+      return std::string(Buffer);
+    }
+    return A->getValue();
+  };
+
   for (const auto *A : Args.filtered(OPT_I, OPT_F, OPT_index_header_map)) {
     if (A->getOption().matches(OPT_index_header_map)) {
       // -index-header-map applies to the next -I or -F.
@@ -3229,16 +3244,7 @@ static bool ParseHeaderSearchArgs(HeaderSearchOptions &Opts, ArgList &Args,
         IsIndexHeaderMap ? frontend::IndexHeaderMap : frontend::Angled;
 
     bool IsFramework = A->getOption().matches(OPT_F);
-    std::string Path = A->getValue();
-
-    if (IsSysrootSpecified && !IsFramework && A->getValue()[0] == '=') {
-      SmallString<32> Buffer;
-      llvm::sys::path::append(Buffer, Opts.Sysroot,
-                              llvm::StringRef(A->getValue()).substr(1));
-      Path = std::string(Buffer);
-    }
-
-    Opts.AddPath(Path, Group, IsFramework,
+    Opts.AddPath(ConvertHeaderPath(A, IsFramework), Group, IsFramework,
                  /*IgnoreSysroot*/ true);
     IsIndexHeaderMap = false;
   }
@@ -3256,12 +3262,14 @@ static bool ParseHeaderSearchArgs(HeaderSearchOptions &Opts, ArgList &Args,
   }
 
   for (const auto *A : Args.filtered(OPT_idirafter))
-    Opts.AddPath(A->getValue(), frontend::After, false, true);
+    Opts.AddPath(ConvertHeaderPath(A), frontend::After, false, true);
   for (const auto *A : Args.filtered(OPT_iquote))
-    Opts.AddPath(A->getValue(), frontend::Quoted, false, true);
-  for (const auto *A : Args.filtered(OPT_isystem, OPT_iwithsysroot))
+    Opts.AddPath(ConvertHeaderPath(A), frontend::Quoted, false, true);
+  for (const auto *A : Args.filtered(OPT_iwithsysroot))
     Opts.AddPath(A->getValue(), frontend::System, false,
-                 !A->getOption().matches(OPT_iwithsysroot));
+                 /*IgnoreSysRoot=*/false);
+  for (const auto *A : Args.filtered(OPT_isystem))
+    Opts.AddPath(ConvertHeaderPath(A), frontend::System, false, true);
   for (const auto *A : Args.filtered(OPT_iframework))
     Opts.AddPath(A->getValue(), frontend::System, true, true);
   for (const auto *A : Args.filtered(OPT_iframeworkwithsysroot))
diff --git a/clang/test/Preprocessor/sysroot-prefix.c b/clang/test/Preprocessor/sysroot-prefix.c
index 08c72f53b44e9f..ce19790819b732 100644
--- a/clang/test/Preprocessor/sysroot-prefix.c
+++ b/clang/test/Preprocessor/sysroot-prefix.c
@@ -4,6 +4,12 @@
 // RUN: %clang_cc1 -v -isysroot /var/empty -I =null -E %s -o /dev/null 2>&1 | FileCheck -check-prefix CHECK-ISYSROOT_SYSROOT_NULL %s
 // RUN: %clang_cc1 -v -isysroot /var/empty -isysroot /var/empty/root -I =null -E %s -o /dev/null 2>&1 | FileCheck -check-prefix CHECK-ISYSROOT_ISYSROOT_SYSROOT_NULL %s
 // RUN: %clang_cc1 -v -isysroot /var/empty/root -isysroot /var/empty -I =null -E %s -o /dev/null 2>&1 | FileCheck -check-prefix CHECK-ISYSROOT_ISYSROOT_SWAPPED_SYSROOT_NULL %s
+// RUN: %clang_cc1 -v -isystem=/usr/include -isysroot /var/empty -E %s -o /dev/null 2>&1 | FileCheck -check-prefix CHECK-ISYSROOT_ISYSTEM_SYSROOT %s
+// RUN: %clang_cc1 -v -isystem=/usr/include -E %s -o /dev/null 2>&1 | FileCheck -check-prefix CHECK-ISYSROOT_ISYSTEM_NO_SYSROOT %s
+// RUN: %clang_cc1 -v -iquote=/usr/include -isysroot /var/empty  -E %s -o /dev/null 2>&1 | FileCheck -check-prefix CHECK-ISYSROOT_IQUOTE_SYSROOT %s
+// RUN: %clang_cc1 -v -iquote=/usr/include -E %s -o /dev/null 2>&1 | FileCheck -check-prefix CHECK-ISYSROOT_IQUOTE_NO_SYSROOT %s
+// RUN: %clang_cc1 -v -idirafter=/usr/include -isysroot /var/empty  -E %s -o /dev/null 2>&1 | FileCheck -check-prefix CHECK-ISYSROOT_IDIRAFTER_SYSROOT %s
+// RUN: %clang_cc1 -v -idirafter=/usr/include -E %s -o /dev/null 2>&1 | FileCheck -check-prefix CHECK-ISYSROOT_IDIRAFTER_NO_SYSROOT %s
 
 // CHECK-ISYSROOT_NO_SYSROOT: ignoring nonexistent directory "/var/empty/include"
 // CHECK-ISYSROOT_NO_SYSROOT-NOT: ignoring nonexistent directory "/var/empty/var/empty/include"
@@ -23,3 +29,11 @@
 // CHECK-ISYSROOT_ISYSROOT_SWAPPED_SYSROOT_NULL: ignoring nonexistent directory "/var/empty{{.}}null"
 // CHECK-ISYSROOT_ISYSROOT_SWAPPED_SYSROOT_NULL-NOT: ignoring nonexistent directory "=null"
 
+// CHECK-ISYSROOT_ISYSTEM_SYSROOT: ignoring nonexistent directory "/var/empty/usr/include"
+// CHECK-ISYSROOT_ISYSTEM_NO_SYSROOT: ignoring nonexistent directory "=/usr/include"
+
+// CHECK-ISYSROOT_IQUOTE_SYSROOT: ignoring nonexistent directory "/var/empty/usr/include"
+// CHECK-ISYSROOT_IQUOTE_NO_SYSROOT: ignoring nonexistent directory "=/usr/include"
+
+// CHECK-ISYSROOT_IDIRAFTER_SYSROOT: ignoring nonexistent directory "/var/empty/usr/include"
+// CHECK-ISYSROOT_IDIRAFTER_NO_SYSROOT: ignoring nonexistent directory "=/usr/include"

[jansvoboda11]

Instead of prefixing the path with sysroot here, would it make sense to defer to InitHeaderSearch::AddPath() by calling Opts.AddPath(..., /*IgnoreSysRoot=*/false)? Note that this function only adds the prefix to absolute paths. Does that match GCC behavior?

[etcwilde]

I had considered doing something like checking whether the first character is an = and if the sysroot option is set and passing true to IgnoreSysRoot when that's the case. It unfortunately does not match behavior. I don't know how useful it is, but --sysroot /foo/bar -isystem=baz will result in the searchpath /foo/barbaz in gcc. (that's actually a good testcase, I should add that).

Given that we still need to strip the leading = from the searchpath with -isystem though not with -iwithsysroot, and that we want to match the -I= behavior, I decided to stick with this to minimize the impact of the patch. I could try to hunt down all of the places where the UserEntries list is iterated and ensure that they're doing the appropriate sysroot prefixing for the corresponding flags.

[jansvoboda11]

LGTM