Compilation: avoid Cache hash dependency on zig lib path

 * Update for the breaking changes to std.fs.path.resolve. This had a
   happy side effect of deleting some error handling code which is no
   longer needed.
 * Introduce cache_exempt_flags field to CSourceFile. This is used only
   for include directories when building libc++ and libc++abi which
   depend only on the zig lib path.
 * libc_include_dir_list is only added to the cache hash when it
   contains directories which have been obtained from system probing. It
   is exempt when the directories depend only on the zig lib path.

2 files changed, 43 insertions, 27 deletions

diff --git a/src/Compilation.zig b/src/Compilation.zig
index 2c94785618..795eb493e2 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -201,7 +201,9 @@ pub const CRTFile = struct {
 /// For passing to a C compiler.
 pub const CSourceFile = struct {
     src_path: []const u8,
-    extra_flags: []const []const u8 = &[0][]const u8{},
+    extra_flags: []const []const u8 = &.{},
+    /// Same as extra_flags except they are not added to the Cache hash.
+    cache_exempt_flags: []const []const u8 = &.{},
 };
 
 const Job = union(enum) {
@@ -3251,13 +3253,6 @@ fn processOneJob(comp: *Compilation, job: Job) !void {
 
             const module = comp.bin_file.options.module.?;
             module.semaPkg(pkg) catch |err| switch (err) {
-                error.CurrentWorkingDirectoryUnlinked,
-                error.Unexpected,
-                => comp.lockAndSetMiscFailure(
-                    .analyze_pkg,
-                    "unexpected problem analyzing package '{s}'",
-                    .{pkg.root_src_path},
-                ),
                 error.OutOfMemory => return error.OutOfMemory,
                 error.AnalysisFail => return,
             };
@@ -3562,7 +3557,14 @@ pub fn obtainCObjectCacheManifest(comp: *const Compilation) Cache.Manifest {
     man.hash.add(comp.sanitize_c);
     man.hash.addListOfBytes(comp.clang_argv);
     man.hash.add(comp.bin_file.options.link_libcpp);
-    man.hash.addListOfBytes(comp.libc_include_dir_list);
+
+    // When libc_installation is null it means that Zig generated this dir list
+    // based on the zig library directory alone. The zig lib directory file
+    // path is purposefully either in the cache or not in the cache. The
+    // decision should not be overridden here.
+    if (comp.bin_file.options.libc_installation != null) {
+        man.hash.addListOfBytes(comp.libc_include_dir_list);
+    }
 
     return man;
 }
@@ -3949,6 +3951,7 @@ fn updateCObject(comp: *Compilation, c_object: *CObject, c_obj_prog_node: *std.P
         {
             try comp.addCCArgs(arena, &argv, ext, null);
             try argv.appendSlice(c_object.src.extra_flags);
+            try argv.appendSlice(c_object.src.cache_exempt_flags);
 
             const out_obj_path = if (comp.bin_file.options.emit) |emit|
                 try emit.directory.join(arena, &.{emit.sub_path})
@@ -3990,6 +3993,7 @@ fn updateCObject(comp: *Compilation, c_object: *CObject, c_obj_prog_node: *std.P
             try std.fmt.allocPrint(arena, "{s}.d", .{out_obj_path});
         try comp.addCCArgs(arena, &argv, ext, out_dep_path);
         try argv.appendSlice(c_object.src.extra_flags);
+        try argv.appendSlice(c_object.src.cache_exempt_flags);
 
         try argv.ensureUnusedCapacity(5);
         switch (comp.clang_preprocessor_mode) {
diff --git a/src/libcxx.zig b/src/libcxx.zig
index 850da698c5..7ca405cf15 100644
--- a/src/libcxx.zig
+++ b/src/libcxx.zig
@@ -187,15 +187,6 @@ pub fn buildLibCXX(comp: *Compilation) !void {
             try cflags.append("-faligned-allocation");
         }
 
-        try cflags.append("-I");
-        try cflags.append(cxx_include_path);
-
-        try cflags.append("-I");
-        try cflags.append(cxxabi_include_path);
-
-        try cflags.append("-I");
-        try cflags.append(cxx_src_include_path);
-
         if (target_util.supports_fpic(target)) {
             try cflags.append("-fPIC");
         }
@@ -203,9 +194,24 @@ pub fn buildLibCXX(comp: *Compilation) !void {
         try cflags.append("-std=c++20");
         try cflags.append("-Wno-user-defined-literals");
 
+        // These depend on only the zig lib directory file path, which is
+        // purposefully either in the cache or not in the cache. The decision
+        // should not be overridden here.
+        var cache_exempt_flags = std.ArrayList([]const u8).init(arena);
+
+        try cache_exempt_flags.append("-I");
+        try cache_exempt_flags.append(cxx_include_path);
+
+        try cache_exempt_flags.append("-I");
+        try cache_exempt_flags.append(cxxabi_include_path);
+
+        try cache_exempt_flags.append("-I");
+        try cache_exempt_flags.append(cxx_src_include_path);
+
         c_source_files.appendAssumeCapacity(.{
             .src_path = try comp.zig_lib_directory.join(arena, &[_][]const u8{ "libcxx", cxx_src }),
             .extra_flags = cflags.items,
+            .cache_exempt_flags = cache_exempt_flags.items,
         });
     }
 
@@ -340,15 +346,6 @@ pub fn buildLibCXXABI(comp: *Compilation) !void {
             try cflags.append("-D_LIBCPP_HAS_MUSL_LIBC");
         }
 
-        try cflags.append("-I");
-        try cflags.append(cxxabi_include_path);
-
-        try cflags.append("-I");
-        try cflags.append(cxx_include_path);
-
-        try cflags.append("-I");
-        try cflags.append(cxx_src_include_path);
-
         if (target_util.supports_fpic(target)) {
             try cflags.append("-fPIC");
         }
@@ -357,9 +354,24 @@ pub fn buildLibCXXABI(comp: *Compilation) !void {
         try cflags.append("-funwind-tables");
         try cflags.append("-std=c++20");
 
+        // These depend on only the zig lib directory file path, which is
+        // purposefully either in the cache or not in the cache. The decision
+        // should not be overridden here.
+        var cache_exempt_flags = std.ArrayList([]const u8).init(arena);
+
+        try cache_exempt_flags.append("-I");
+        try cache_exempt_flags.append(cxxabi_include_path);
+
+        try cache_exempt_flags.append("-I");
+        try cache_exempt_flags.append(cxx_include_path);
+
+        try cache_exempt_flags.append("-I");
+        try cache_exempt_flags.append(cxx_src_include_path);
+
         c_source_files.appendAssumeCapacity(.{
             .src_path = try comp.zig_lib_directory.join(arena, &[_][]const u8{ "libcxxabi", cxxabi_src }),
             .extra_flags = cflags.items,
+            .cache_exempt_flags = cache_exempt_flags.items,
         });
     }