[CI] Setup generate_report to describe ninja failures

.ci/generate_test_report_lib.py

@@ -12,6 +12,57 @@
     "https://github.com/llvm/llvm-project/issues and add the "
     "`infrastructure` label."
 )
+# The maximum number of lines to pull from a ninja failure.
+NINJA_LOG_SIZE_THRESHOLD = 500
+
+
+def _parse_ninja_log(ninja_log: list[str]) -> list[tuple[str, str]]:
+    """Parses an individual ninja log."""
+    failures = []
+    index = 0
+    while index < len(ninja_log):
+        while index < len(ninja_log) and not ninja_log[index].startswith("FAILED:"):
+            index += 1
+        if index == len(ninja_log):
+            # We hit the end of the log without finding a build failure, go to
+            # the next log.
+            return failures
+        failing_action = ninja_log[index - 1].split("] ")[1]
+        failure_log = []
+        while (
+            index < len(ninja_log)
+            and not ninja_log[index].startswith("[")
+            and not ninja_log[index].startswith(
+                "ninja: build stopped: subcommand failed"
+            )
+            and len(failure_log) < NINJA_LOG_SIZE_THRESHOLD
+        ):
+            failure_log.append(ninja_log[index])
+            index += 1
+        failures.append((failing_action, "\n".join(failure_log)))
+    return failures
+
+
+def find_failure_in_ninja_logs(ninja_logs: list[list[str]]) -> list[tuple[str, str]]:
+    """Extracts failure messages from ninja output.
+
+    This patch takes stdout/stderr from ninja in the form of a list of files
+    represented as a list of lines. This function then returns tuples containing
+    the name of the target and the error message.
+
+    Args:
+      ninja_logs: A list of files in the form of a list of lines representing the log
+        files captured from ninja.
+
+    Returns:
+      A list of tuples. The first string is the name of the target that failed. The
+      second string is the error message.
+    """
+    failures = []
+    for ninja_log in ninja_logs:
+        log_failures = _parse_ninja_log(ninja_log)
+        failures.extend(log_failures)
+    return failures
 
 
 # Set size_limit to limit the byte size of the report. The default is 1MB as this
@@ -24,6 +75,7 @@ def generate_report(
     title,
     return_code,
     junit_objects,
+    ninja_logs: list[list[str]],
     size_limit=1024 * 1024,
     list_failures=True,
 ):
@@ -61,15 +113,46 @@ def generate_report(
                 ]
             )
         else:
-            report.extend(
-                [
-                    "The build failed before running any tests.",
-                    "",
-                    SEE_BUILD_FILE_STR,
-                    "",
-                    UNRELATED_FAILURES_STR,
-                ]
-            )
+            ninja_failures = find_failure_in_ninja_logs(ninja_logs)
+            if not ninja_failures:
+                report.extend(
+                    [
+                        "The build failed before running any tests. Detailed "
+                        "information about the build failure could not be "
+                        "automatically obtained.",
+                        "",
+                        SEE_BUILD_FILE_STR,
+                        "",
+                        UNRELATED_FAILURES_STR,
+                    ]
+                )
+            else:
+                report.extend(
+                    [
+                        "The build failed before running any tests. Click on the "
+                        "failure below to see the details.",
+                        "",
+                    ]
+                )
+                for build_failure in ninja_failures:
+                    failed_action, failure_message = build_failure
+                    report.extend(
+                        [
+                            "<details>",
+                            f"<summary>{failed_action}</summary>",
+                            "",
+                            "```",
+                            failure_message,
+                            "```",
+                            "</details>",
+                        ]
+                    )
+                report.extend(
+                    [
+                        "",
+                        UNRELATED_FAILURES_STR,
+                    ]
+                )
         return "\n".join(report)
 
     tests_passed = tests_run - tests_skipped - tests_failed
@@ -114,14 +197,32 @@ def plural(num_tests):
     elif return_code != 0:
         # No tests failed but the build was in a failed state. Bring this to the user's
         # attention.
-        report.extend(
-            [
-                "",
-                "All tests passed but another part of the build **failed**.",
-                "",
-                SEE_BUILD_FILE_STR,
-            ]
-        )
+        ninja_failures = find_failure_in_ninja_logs(ninja_logs)
+        if not ninja_failures:
+            report.extend(
+                [
+                    "",
+                    "All tests passed but another part of the build **failed**. "
+                    "Detailed information about the build failure could not be "
+                    "automatically obtained.",
+                    "",
+                    SEE_BUILD_FILE_STR,
+                ]
+            )
+        else:
+            for build_failure in ninja_failures:
+                failed_action, failure_message = build_failure
+                report.extend(
+                    [
+                        "<details>",
+                        f"<summary>{failed_action}</summary>",
+                        "",
+                        "```",
+                        failure_message,
+                        "```",
+                        "</details>",
+                    ]
+                )
 
     if failures or return_code != 0:
         report.extend(["", UNRELATED_FAILURES_STR])