fix(coverage): stop reporting a duplicate range and a line past EOF (#963)

scripts/setup-windows.ps1 has 326 lines and its parse-coverage report read
"113-113,113-113,245-327" — the same line named twice, and an end line that
does not exist. Two separate faults, both in cbm_error_regions_push.

Past-EOF end line. A tree-sitter node that ends at column 0 stopped right
after the previous line's newline, so it holds no text on the row it points
at. Adding 1 to that row named a line past the end of the file whenever the
region ran to EOF. The node here is start=(244,2) end=(326,0). Clamp the end
to the row above when the end column is 0 and the node spans more than one
row.

Duplicate range. Line 113 carries two separate ERROR nodes, at columns 25-29
and 31-32, and each pushed its own range. A line range says nothing new the
second time. Merge a region that overlaps the one already open instead of
repeating it. The walk visits children in source order, so a region starting
at or before the open range's end really does overlap it. The merge runs
BEFORE the cap check, so it is never miscounted as a dropped range.

The real file now reports "113-113,245-326".

Two tests, both proved RED first with the exact expected text:
  coverage_repeated_error_line_reports_one_range_issue963  "2-2,2-2" != "2-2"
  coverage_range_never_ends_past_the_last_line_issue963    "1-5"    != "1-4"

Full suite: 7798 passed, 2 failed — both pre-existing agent-client install
assertions in tests/test_cli.c, unrelated to this change.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: Joshua Richter <jrichter5781@gmail.com>

Author: CaptainMittens

internal/cbm/cbm.c

@@ -790,12 +790,38 @@ typedef struct {
 } cbm_error_regions_t;
 
 static void cbm_error_regions_push(cbm_error_regions_t *acc, TSNode n) {
+    TSPoint start = ts_node_start_point(n);
+    TSPoint end = ts_node_end_point(n);
+    uint32_t start_line = start.row + 1;
+    uint32_t end_line = end.row + 1;
+
+    /* A node that ends at column 0 stopped right after the previous line's
+     * newline, so it holds no text on the row it points at. Counting that row
+     * named a line past the end of the file whenever the region ran to EOF:
+     * scripts/setup-windows.ps1 has 326 lines and reported "245-327". */
+    if (end.column == 0 && end.row > start.row) {
+        end_line = end.row;
+    }
+
+    /* One line can carry several error nodes, and a line range says nothing
+     * new the second time. Line 113 of scripts/setup-windows.ps1 has two, and
+     * the report read "113-113,113-113". Extend the range already open instead
+     * of repeating it. The walk visits children in source order, so a region
+     * that starts at or before the open range's end really does overlap it.
+     * This runs BEFORE the cap check, so a merge never counts as a drop. */
+    if (acc->count > 0 && start_line <= acc->ends[acc->count - 1]) {
+        if (end_line > acc->ends[acc->count - 1]) {
+            acc->ends[acc->count - 1] = end_line;
+        }
+        return;
+    }
+
     if (acc->count >= CBM_MAX_ERROR_REGIONS) {
         acc->dropped++;
         return;
     }
-    acc->starts[acc->count] = ts_node_start_point(n).row + 1;
-    acc->ends[acc->count] = ts_node_end_point(n).row + 1;
+    acc->starts[acc->count] = start_line;
+    acc->ends[acc->count] = end_line;
     acc->count++;
 }
 

tests/test_parse_coverage.c

@@ -711,6 +711,51 @@ TEST(c_thread_local_grammar_limit_is_pinned_issue963) {
     PASS();
 }
 
+/* Two error nodes can sit on ONE line. Line 113 of scripts/setup-windows.ps1
+ * does exactly that, and the report used to read "113-113,113-113" — the same
+ * line named twice. A line range says nothing new the second time, so repeated
+ * or overlapping regions must collapse into one. */
+static const char *PS_TWO_ERRORS_ONE_LINE = "Write-Host \"start\"\n"             /* 1 */
+                                            "wsl.exe -- bash -c $Command 2>&1\n" /* 2 */
+                                            "Write-Host \"end\"\n";              /* 3 */
+
+/* An error region that runs to the end of the file stops just after the last
+ * newline. Tree-sitter calls that position row N, column 0 — a row that holds
+ * no text. Reading it as a line number named a line past the end of the file:
+ * scripts/setup-windows.ps1 has 326 lines and the report said "245-327". */
+static const char *PS_ERROR_TO_EOF = "} else {\n"             /* 1 */
+                                     "    if ($a) {\n"        /* 2 */
+                                     "        Write-Host x\n" /* 3 */
+                                     "}\n";                   /* 4 */
+
+TEST(coverage_repeated_error_line_reports_one_range_issue963) {
+    CBMFileResult *r =
+        cbm_extract_file(PS_TWO_ERRORS_ONE_LINE, (int)strlen(PS_TWO_ERRORS_ONE_LINE),
+                         CBM_LANG_POWERSHELL, "covproj", "two_errors.ps1", 0, NULL, NULL);
+    ASSERT_NOT_NULL(r);
+    ASSERT_TRUE(r->parse_incomplete);
+    ASSERT_NOT_NULL(r->error_ranges);
+    /* Line 2 carries two separate error nodes. It must be named once. */
+    ASSERT_STR_EQ(r->error_ranges, "2-2");
+    ASSERT_EQ(r->error_region_count, 1);
+    cbm_free_result(r);
+    PASS();
+}
+
+TEST(coverage_range_never_ends_past_the_last_line_issue963) {
+    int len = (int)strlen(PS_ERROR_TO_EOF);
+    CBMFileResult *r = cbm_extract_file(PS_ERROR_TO_EOF, len, CBM_LANG_POWERSHELL, "covproj",
+                                        "error_to_eof.ps1", 0, NULL, NULL);
+    ASSERT_NOT_NULL(r);
+    ASSERT_TRUE(r->parse_incomplete);
+    ASSERT_NOT_NULL(r->error_ranges);
+    /* The file has four lines and ends with a newline. Line 5 does not exist. */
+    ASSERT_STR_EQ(r->error_ranges, "1-4");
+    ASSERT_NULL(strstr(r->error_ranges, "5"));
+    cbm_free_result(r);
+    PASS();
+}
+
 SUITE(parse_coverage) {
     RUN_TEST(c_ifdef_split_brace_sets_parse_incomplete);
     RUN_TEST(c_ifdef_split_brace_neighbors_still_extracted);
@@ -742,4 +787,6 @@ SUITE(parse_coverage) {
     RUN_TEST(c_refinement_does_not_suppress_real_garbage);
     RUN_TEST(c_clean_file_stays_unflagged_after_refinement);
     RUN_TEST(c_thread_local_grammar_limit_is_pinned_issue963);
+    RUN_TEST(coverage_repeated_error_line_reports_one_range_issue963);
+    RUN_TEST(coverage_range_never_ends_past_the_last_line_issue963);
 }