[clang] Add support for sysroot-relative system header search paths (PR #82084)

[Evan Wilde via cfe-commits]

https://github.com/etcwilde created https://github.com/llvm/llvm-project/pull/82084

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.

>From 37bcd5380893cb489c012508613919fa05254a94 Mon Sep 17 00:00:00 2001
From: Evan Wilde <etceterawilde at gmail.com>
Date: Fri, 16 Feb 2024 16:39:10 -0800
Subject: [PATCH] Support sysroot-relative header search paths

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`.
---
 clang/lib/Frontend/CompilerInvocation.cpp | 36 ++++++++++++++---------
 clang/test/Preprocessor/sysroot-prefix.c  | 14 +++++++++
 2 files changed, 36 insertions(+), 14 deletions(-)

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"