incremental compilation: reached unreachable code and accumulation of errors if @importing non-existent files

[llogick]

Zig Version

0.14.0-dev.3020+c104e8644 DEBUG build

Steps to Reproduce and Observed Behavior

Start out with a zig init project
Add a "check" step for the exe
build with zig build -fincremental --watch check
Add an @import to a non existent file in src/main.zig, eg const argh = @import("blah.zig");
Save main.zig (compiler will report src/main.zig:x:y: error: unable to load 'src/blah.zig': FileNotFound)
Modify the @import string, eg delete the 'g' -> const argh = @import("blah.zi");
Save main.zig

zig build -fincremental --watch check
Build Summary: 2/2 steps succeeded
check success
└─ zig build-exe zig-init Debug native success 2s
check
└─ zig build-exe zig-init Debug native 1 errors
src/main.zig:5:22: error: unable to load 'src/blah.zig': FileNotFound
const argh = @import("blah.zig");
                     ^~~~~~~~~~
error: 1 compilation errors
Build Summary: 0/2 steps succeeded; 1 failed
check transitive failure
└─ zig build-exe zig-init Debug native 1 errors
check
└─ zig build-exe zig-init Debug native failure
error: thread 413716 panic: reached unreachable code
/home/rad/lab/zig/build/stage4/lib/zig/std/posix.zig:1820:23: 0x6063fdf in openatZ (zig)
            .NOENT => return error.FileNotFound,
                      ^
/home/rad/lab/zig/build/stage4/lib/zig/std/fs/Dir.zig:886:16: 0x5ed8d12 in openFileZ (zig)
    const fd = try posix.openatZ(self.fd, sub_path, os_flags, 0);
               ^
/home/rad/lab/zig/build/stage4/lib/zig/std/fs/Dir.zig:833:5: 0x5d3db85 in openFile (zig)
    return self.openFileZ(&path_c, flags);
    ^
/home/rad/lab/zig/build/stage4/lib/zig/std/Build/Cache/Path.zig:62:5: 0x5dea14d in openFile (zig)
    return p.root_dir.handle.openFile(joined_path, flags);
    ^
/home/rad/lab/zig/src/Zcu/PerThread.zig:92:23: 0x66d5013 in astGenFile (zig)
    var source_file = try file.mod.root.openFile(file.sub_file_path, .{});
                      ^
/home/rad/lab/zig/build/stage4/lib/zig/std/debug.zig:518:14: 0x5d37eed in assert (zig)
    if (!ok) unreachable; // assertion failure
             ^
/home/rad/lab/zig/build/stage4/lib/zig/std/array_hash_map.zig:966:19: 0x62ff86d in putNoClobberContext (zig)
            assert(!result.found_existing);
                  ^
/home/rad/lab/zig/build/stage4/lib/zig/std/array_hash_map.zig:962:44: 0x60d7cd1 in putNoClobber (zig)
            return self.putNoClobberContext(gpa, key, value, undefined);
                                           ^
/home/rad/lab/zig/src/Zcu/PerThread.zig:3241:42: 0x66d75f4 in reportRetryableAstGenError (zig)
        try zcu.failed_files.putNoClobber(gpa, file, err_msg);
                                         ^
/home/rad/lab/zig/src/Compilation.zig:4284:42: 0x62fb2c2 in workerAstGenFile (zig)
            pt.reportRetryableAstGenError(src, file_index, err) catch |oom| switch (oom) {
                                         ^
/home/rad/lab/zig/build/stage4/lib/zig/std/Thread/Pool.zig:182:50: 0x62fb9ee in runFn (zig)
            @call(.auto, func, .{id.?} ++ closure.arguments);
                                                 ^
/home/rad/lab/zig/build/stage4/lib/zig/std/Thread/Pool.zig:295:32: 0x62a9364 in worker (zig)
            run_node.data.runFn(&run_node.data, id);
                               ^
/home/rad/lab/zig/build/stage4/lib/zig/std/Thread.zig:488:13: 0x608cc2a in callFn__anon_175265 (zig)
            @call(.auto, f, args);
            ^
/home/rad/lab/zig/build/stage4/lib/zig/std/Thread.zig:757:30: 0x5f14c24 in entryFn (zig)
                return callFn(f, args_ptr.*);
                             ^
???:?:?: 0x7f10e6098291 in ??? (libc.so.6)
Unwind information for `libc.so.6:0x7f10e6098291` was not available, trace may be incomplete


error: the following command terminated unexpectedly:
/home/rad/lab/zig/build/stage5/bin/zig build-exe -ODebug -Mroot=/home/rad/lab/zta/misc/zig-init/src/main.zig -fno-emit-bin --cache-dir /home/rad/lab/zta/misc/zig-init/.zig-cache --global-cache-dir /home/rad/.cache/zig --name zig-init --zig-lib-dir /home/rad/lab/zig/build/stage5/lib/zig/ -fincremental --listen=- 

A (Zig) Release build will just continue to report (even if you comment out the import statement)

check
└─ zig build-exe zig-init Debug native 1 errors
error: unable to load 'src/blah.zig': FileNotFound
error: 1 compilation errors
Build Summary: 0/2 steps succeeded; 1 failed

Modifying the import statement causes accumulation of errors to nonexistent files

check transitive failure
└─ zig build-exe zig-init Debug native 2 errors
check
└─ zig build-exe zig-init Debug native 3 errors
error: unable to load 'src/blah.zig': FileNotFound
error: unable to load 'src/bleh.zig': FileNotFound
src/main.zig:5:22: error: unable to load 'src/hmm.zig': FileNotFound
const argh = @import("hmm.zig");
                     ^~~~~~~~~
error: 3 compilation errors
Build Summary: 0/2 steps succeeded; 1 failed
check transitive failure
└─ zig build-exe zig-init Debug native 3 errors
check
└─ zig build-exe zig-init Debug native 3 errors
error: unable to load 'src/blah.zig': FileNotFound
error: unable to load 'src/bleh.zig': FileNotFound
error: unable to load 'src/hmm.zig': FileNotFound
error: 3 compilation errors

Expected Behavior