preprocessor: fix comparator regex for column-aligned stats output

The patternComparator for the log-statistics-from-the-cue-evaluator page
used the regex (?m)\d+,?$ which only normalizes digits at line ends. CUE
evaluator stats use right-aligned columns, so when numbers change digit
count between runs the whitespace padding before them also changes. This
caused the comparator to fail, rewriting the page on every run when
Preprocessor-No-Write-Cache was set.

Change the regex to (?m)\s+\d+,?$ so that both the whitespace padding
and the digits are normalized together, correctly handling column
alignment differences.

Add a test that verifies comparators handle column-aligned output with
different digit counts when --nowritecache is set with a cache miss.

Signed-off-by: Paul Jolly <paul@myitcv.io>
Change-Id: Ifdec2fbafcf3d013bcffa09a8024d0af4417869c
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cuelang.org/+/1232616
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

Author: myitcv

content/docs/howto/log-statistics-from-the-cue-evaluator/page.cue

@@ -4,6 +4,6 @@ content: docs: howto: "log-statistics-from-the-cue-evaluator": {
 	page: comparators: [{
 		kind:          "patternComparator"
 		commandPrefix: "cat stats.cue"
-		pattern: expr: #"(?m)\d+,?$"#
+		pattern: expr: #"(?m)\s+\d+,?$"#
 	}]
 }

internal/cmd/preprocessor/cmd/testdata/execute_comparators_nowritecache_aligned.txtar

@@ -0,0 +1,87 @@
+# Test that preprocessor comparators correctly handle column-aligned output
+# when --nowritecache is set with a cache miss, specifically when numbers
+# have different digit counts between the cached and actual outputs.
+#
+# CUE evaluator stats output uses right-aligned numeric columns. When numbers
+# change digit count between runs, the column padding (spaces before numbers)
+# changes too. A comparator pattern of (?m)\d+,?$ only normalizes digits,
+# not the preceding whitespace, causing false mismatches. The fix is to use
+# (?m)\s+\d+,?$ which normalizes both the whitespace padding and the digits.
+
+unquote content/dir/en.md
+
+# Run the preprocessor to generate initial cache and output files.
+exec preprocessor execute --debug=all
+
+# Save copies
+cp content/dir/en.md content/dir/en.md.original
+
+# Modify gen_cache.cue to:
+# 1. Change the hash to trigger cache miss (simulating preprocessor change)
+# 2. Change the cached step output to have different digit counts:
+#   FieldA: "42" (2 digits) -> "1" (1 digit)
+#   FieldB: "123456" (6 digits) -> "1" (1 digit)
+#   FieldC: "7" (1 digit) -> "12345" (5 digits)
+exec sed -i 's/hash:       "[^"]*"/hash:       "INVALIDHASHVALUE"/' content/dir/gen_cache.cue
+exec sed -i 's/FieldA:        42/FieldA:         1/' content/dir/gen_cache.cue
+exec sed -i 's/FieldB:    123456/FieldB:         1/' content/dir/gen_cache.cue
+exec sed -i 's/FieldC:         7/FieldC:     12345/' content/dir/gen_cache.cue
+cp content/dir/gen_cache.cue content/dir/gen_cache.cue.modified
+
+# Run with --nowritecache. The script re-runs (cache miss) and produces
+# the original output. The comparator normalizes both the actual and
+# cached outputs (including whitespace padding) and determines they're
+# equivalent, then uses the cached version.
+exec preprocessor execute --debug=all --nowritecache
+stderr $WORK${/}'content'${/}'dir'${/}'en.md: cache miss for multi-step script'
+
+# gen_cache.cue was NOT updated (nowritecache prevented it)
+cmp content/dir/gen_cache.cue content/dir/gen_cache.cue.modified
+
+# Source file was not changed
+cmp content/dir/en.md content/dir/en.md.original
+
+# The target file should contain the CACHED version of the output (with the
+# modified numbers), because the comparator determined equivalence between
+# actual and cached outputs despite different digit counts in column-aligned
+# fields. If the target instead has the original numbers, the comparator
+# failed to handle the whitespace/digit-count variation.
+exec grep 'FieldA:         1' hugo/content/en/dir/index.md
+
+-- hugo/.keep --
+-- site.cue --
+package site
+
+import "strings"
+
+versions: cue: [x=string]: var: "CUELANG_CUE_\(strings.ToUpper(x))"
+
+versions: cue: default: v: "v0.9.0-alpha.3"
+-- content/dir/page.cue --
+package site
+
+content: dir: page: {
+	leftDelim:  "{{{"
+	rightDelim: "}}}"
+
+	comparators: [{
+		kind:          "patternComparator"
+		commandPrefix: "cat stats.txt"
+		pattern: expr: #"(?m)\s+\d+,?$"#
+	}]
+}
+-- content/dir/en.md --
+>---
+>title: Stats Test
+>---
+>{{{with upload "en" "stats file"}}}
+>-- stats.txt --
+>Stats: {
+>	FieldA:        42
+>	FieldB:    123456
+>	FieldC:         7
+>}
+>{{{end}}}
+>{{{with script "en" "read stats"}}}
+>cat stats.txt
+>{{{end}}}