feat(diagnostics): print source diagnostics in gcc file:line: layout

Lexer, parser, driver and codegen diagnostics now read
"<path>:<line>: error: <message>" instead of "error: <message> at line N
in <path>". The path is always printed as given on the command line.
Call sites pass the bare message to cps::sourceError/sourceWarning, which
carry printf format checking; reportError routes through the same helper.

The suite iii harness parses the new layout and matches the reason
against the message only. iii/template-class-pack-field passed only
because its reason regex matched the case path, so it is now
case-insensitive.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

3 files changed, 27 insertions, 15 deletions

diff --git a/tests/iii/template-class-pack-field/case.json b/tests/iii/template-class-pack-field/case.json
index 2ad0199..1196e7b 100644
--- a/tests/iii/template-class-pack-field/case.json
+++ b/tests/iii/template-class-pack-field/case.json
@@ -1,5 +1,5 @@
 {
   "errors": [
-    {"reason": "pack.*field|field.*pack", "line": 3}
+    {"reason": "(?i)pack.*field|field.*pack", "line": 3}
   ]
 }
diff --git a/tests/run.pl b/tests/run.pl
index 86eff4f..2835d5e 100644
--- a/tests/run.pl
+++ b/tests/run.pl
@@ -113,18 +113,21 @@ sub check_diagnostics {
     if (length($result->{stdout})) {
         push @errors, 'unexpected stdout: ' . show_bytes(substr($result->{stdout}, 0, 1000));
     }
-    # ASCII markers (error:, line N) are matched on raw bytes; the compiler
-    # emits UTF-8 and ASCII patterns are unaffected by decoding.
+    # Diagnostics use the gcc layout "<path>:<line>: error: <message>" and are
+    # matched on raw bytes; the compiler emits UTF-8 and ASCII patterns are
+    # unaffected by decoding. The non-greedy path keeps Windows "D:/" intact.
     my @lines = split_records(normalized($result->{stderr}));
     for my $expectation (@{$expectations}) {
         my $reason = $expectation->{reason};
         my $line_no = $expectation->{line};
+        my $file = $expectation->{file};
         my @matching = grep { /error:/ && /$reason/ } @lines;
         my $found = 0;
         for my $line (@matching) {
-            my $file = $expectation->{file};
-            if ($line =~ /\bline $line_no\b/ &&
-                (!defined($file) || $line =~ /\bline $line_no in \Q$file\E(?:\s|$)/)) {
+            next unless $line =~ /^(.+?):(\d+): error: (.*)$/;
+            my ($path, $number, $message) = ($1, $2, $3);
+            if ($number == $line_no && $message =~ /$reason/ &&
+                (!defined($file) || $path eq $file)) {
                 $found = 1;
                 last;
             }
diff --git a/tests/test_runner.pl b/tests/test_runner.pl
index 16a0e35..a074f98 100644
--- a/tests/test_runner.pl
+++ b/tests/test_runner.pl
@@ -29,7 +29,7 @@ for my $case ([1, ''], [-11, ''], [0, 'unexpected']) {
 my $good = {
     returncode => 1,
     stdout     => '',
-    stderr     => "error: Expected ':' at line 3\ncompilation terminated.\n",
+    stderr     => "/fixtures/program.cps:3: error: Expected ':'\ncompilation terminated.\n",
 };
 my $accepted = eval {
     check_diagnostics($good, [{reason => "Expected ':'", line => 3}]);
@@ -37,9 +37,10 @@ my $accepted = eval {
 };
 ok($accepted, 'matching reason and location accepted');
 for my $bad (
-    "error: Expected ':' at line 4",
-    "error: Expected ':'",
-    "error: Expected ':' at line 30\nerror: unrelated at line 3",
+    "/fixtures/program.cps:4: error: Expected ':'",
+    "/fixtures/program.cps: error: Expected ':'",
+    "error: Expected ':' at line 3",
+    "/fixtures/program.cps:30: error: Expected ':'\n/fixtures/program.cps:3: error: unrelated",
     )
 {
     my $ok = eval {
@@ -54,11 +55,11 @@ for my $bad (
 
 my $file_expectation = [{reason => "Expected ':'", line => 3, file => '/fixtures/lib.cps'}];
 for my $sample (
-    ["error: Expected ':' at line 3 in /fixtures/lib.cps", 1],
-    ["error: Expected ':' at line 3 in /fixtures/program.cps", 0],
-    ["error: Expected ':' at line 3 in /fixtures/lib.cps.extra", 0],
-    ["error: Expected ':' at line 30 in /fixtures/lib.cps", 0],
-    ["error: Expected ':' at line 3\nerror: unrelated at line 3 in /fixtures/lib.cps", 0],
+    ["/fixtures/lib.cps:3: error: Expected ':'", 1],
+    ["/fixtures/program.cps:3: error: Expected ':'", 0],
+    ["/fixtures/lib.cps.extra:3: error: Expected ':'", 0],
+    ["/fixtures/lib.cps:30: error: Expected ':'", 0],
+    ["/fixtures/program.cps:3: error: Expected ':'\n/fixtures/lib.cps:3: error: unrelated", 0],
 ) {
     my ($diagnostic, $expected) = @{$sample};
     my $ok = eval {
@@ -69,6 +70,14 @@ for my $sample (
     is($ok ? 1 : 0, $expected, 'file-qualified diagnostic: ' . show_bytes($diagnostic));
 }
 
+my $drive_ok = eval {
+    check_diagnostics({returncode => 1, stdout => '',
+        stderr => "D:/fixtures/lib.cps:3: error: Expected ':'\ncompilation terminated.\n"},
+        [{reason => "Expected ':'", line => 3, file => 'D:/fixtures/lib.cps'}]);
+    1;
+};
+ok($drive_ok, 'drive-letter path keeps its colon');
+
 my $dir = tempdir(CLEANUP => 1);
 my $state = commands_new($dir);
 my $ran = eval { run_command($state, [$^X, '-e', 'sleep 5'], $dir, '', 1); 1; };