fix: don't offer exact-match completions to prevent readline duplication

When the typed word already exactly matches a command (e.g. 'help'),
return no completions. Readline would append the match, producing
'helphelp'. Partial matches still work normally (e.g. 'he' → 'help').

3 files changed, 408 insertions, 8 deletions

diff --git a/completions/gt.fish b/completions/gt.fish
new file mode 100644
index 0000000..d82e1bb
--- /dev/null
+++ b/completions/gt.fish
@@ -0,0 +1,395 @@
+# SPDX-License-Identifier: MIT
+# Copyright (c) 2026 Paul Buetow
+
+# Fish shell completions for gt — a command-line calculator with RPN and
+# percentage arithmetic.
+#
+# Install:
+#   cp completions/gt.fish ~/.config/fish/completions/
+#   # or system-wide:
+#   sudo cp completions/gt.fish /usr/local/share/fish/vendor_completions.d/
+
+# ── Helpers ──────────────────────────────────────────────────────────────────
+
+# Return true when we are at the top-level (first argument after 'gt').
+function __fish_gt_needs_top_level
+    # Only match if we haven't seen any subcommand or flag yet
+    not __fish_seen_command_argument --exclusive
+end
+
+# Return true when the current token is part of an RPN expression (i.e. we are
+# NOT inside 'metric …' or 'custom …' subcommand trees that have their own
+# completions).  Used as a condition for completing operators / constants /
+# units anywhere in the expression.
+function __fish_gt_not_in_metric_or_custom
+    not __fish_seen_subcommand_from metric custom
+end
+
+# ── Flags ────────────────────────────────────────────────────────────────────
+
+complete -c gt -n "__fish_gt_needs_top_level" \
+    -l log -r -d "Session log file (REPL mode)"
+
+# ── Top-level subcommands ────────────────────────────────────────────────────
+
+complete -c gt -n "__fish_gt_needs_top_level" \
+    -a version -d "Show version"
+
+# ── Expression prefixes ──────────────────────────────────────────────────────
+
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "rpn" -d "RPN expression prefix"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "calc" -d "Calculation prefix (alias)"
+
+# ── Arithmetic operators ─────────────────────────────────────────────────────
+
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "+" -d "Addition"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "-" -d "Subtraction"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "*" -d "Multiplication"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "/" -d "Division"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "^" -d "Power"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "**" -d "Fast integer power"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "%" -d "Modulo"
+
+# ── Logarithmic operators ────────────────────────────────────────────────────
+
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "lg" -d "Log base 2"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "log" -d "Log base 10"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "ln" -d "Natural log"
+
+# ── Comparison operators ─────────────────────────────────────────────────────
+
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "gt" -d "Greater than"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "lt" -d "Less than"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a ">" -d "Greater than"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "<" -d "Less than"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "gte" -d "Greater or equal"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a ">=" -d "Greater or equal"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "lte" -d "Less or equal"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "<=" -d "Less or equal"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "eq" -d "Equal"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "==" -d "Equal"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "neq" -d "Not equal"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "!=" -d "Not equal"
+
+# ── Hyper (n-ary) operators ──────────────────────────────────────────────────
+
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "[+]" -d "Hyper add (n-ary)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "[-]" -d "Hyper subtract (n-ary)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "[*]" -d "Hyper multiply (n-ary)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "[/]" -d "Hyper divide (n-ary)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "[^]" -d "Hyper power (n-ary)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "[%]" -d "Hyper modulo (n-ary)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "[lg]" -d "Hyper log2 (n-ary)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "[log]" -d "Hyper log10 (n-ary)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "[ln]" -d "Hyper ln (n-ary)"
+
+# ── Stack operators ──────────────────────────────────────────────────────────
+
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "dup" -d "Duplicate top of stack"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "swap" -d "Swap top two stack values"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "pop" -d "Discard top of stack"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "d" -d "Delete top two stack values"
+
+# ── Assignment / conversion operators ────────────────────────────────────────
+
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a ":=" -d "Assign right-to-left"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "=:" -d "Assign left-to-right"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "convert" -d "Convert metric unit (with @unit)"
+
+# ── Command operators ────────────────────────────────────────────────────────
+
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "show" -d "Show stack"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "showstack" -d "Show stack (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "print" -d "Show stack (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "vars" -d "List variables"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "constants" -d "List constants"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "clear" -d "Clear all variables"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "clearconstants" -d "Reset constants to defaults"
+
+# ── Boolean literals ─────────────────────────────────────────────────────────
+
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "true" -d "Boolean true (coerces to 1)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "false" -d "Boolean false (coerces to 0)"
+
+# ── Constants ────────────────────────────────────────────────────────────────
+
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "pi" -d "π (3.14159…)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "e" -d "Euler's number (2.71828…)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "euler" -d "Euler's number (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "phi" -d "Golden ratio (1.61803…)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "sqrt2" -d "√2 (1.41421…)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "sqrt3" -d "√3 (1.73205…)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "sqrt5" -d "√5 (2.23606…)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "ln2" -d "ln(2) (0.69314…)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "log2" -d "ln(2) (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "ln10" -d "ln(10) (2.30258…)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "log10" -d "ln(10) (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "log_e" -d "log₁₀(e) (0.43429…)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "log_e10" -d "log₁₀(e) (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "tau" -d "τ = 2π (6.28318…)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "inv_pi" -d "1/π (0.31830…)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "inv_e" -d "1/e (0.36787…)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "inf" -d "Positive infinity"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "infinity" -d "Positive infinity (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "-inf" -d "Negative infinity"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "-infinity" -d "Negative infinity (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "nan" -d "NaN (Not a Number)"
+
+# ── Metric units ─────────────────────────────────────────────────────────────
+
+# DataRate (base: bps)
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "bps" -d "Bits per second"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "Kbps" -d "Kilobits per second"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "Mbps" -d "Megabits per second"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "Gbps" -d "Gigabits per second"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "Tbps" -d "Terabits per second"
+
+# DataSize (base: bits)
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "bits" -d "Bits"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "bytes" -d "Bytes"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "KB" -d "Kilobyte (SI / IEC)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "MB" -d "Megabyte (SI / IEC)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "GB" -d "Gigabyte (SI / IEC)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "TB" -d "Terabyte (SI / IEC)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "PB" -d "Petabyte (SI / IEC)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "KiB" -d "Kibibyte (1024 bytes)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "MiB" -d "Mebibyte (1024 KiB)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "GiB" -d "Gibibyte (1024 MiB)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "TiB" -d "Tebibyte (1024 GiB)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "PiB" -d "Pebibyte (1024 TiB)"
+
+# Time (base: seconds)
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "ms" -d "Milliseconds"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "s" -d "Seconds"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "sec" -d "Seconds (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "secs" -d "Seconds (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "min" -d "Minutes"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "hr" -d "Hours"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "day" -d "Days"
+
+# Weight (base: kilograms)
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "mg" -d "Milligrams"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "g" -d "Grams"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "kg" -d "Kilograms"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "ton" -d "Metric tons"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "lb" -d "Pounds"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "oz" -d "Ounces"
+
+# Speed (base: m/s)
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "mps" -d "Meters per second"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "kmh" -d "Kilometers per hour"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "mph" -d "Miles per hour"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "knots" -d "Knots"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "knot" -d "Knots (alias)"
+
+# Distance (base: meters)
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "m" -d "Meters"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "km" -d "Kilometers"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "mi" -d "Miles"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "mile" -d "Miles (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "miles" -d "Miles (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "ft" -d "Feet"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "foot" -d "Feet (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "feet" -d "Feet (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "in" -d "Inches"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "nm" -d "Nautical miles"
+
+# DataRate aliases (bit/s notation)
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "bit/s" -d "Bits per second (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "kbit/s" -d "Kilobits per second (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "mbit/s" -d "Megabits per second (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "gbit/s" -d "Gigabits per second (alias)"
+complete -c gt -n "__fish_gt_not_in_metric_or_custom" \
+    -a "tbit/s" -d "Terabits per second (alias)"
+
+# ── `metric` subcommand ──────────────────────────────────────────────────────
+
+complete -c gt -n "__fish_seen_subcommand_from metric" \
+    -a "show" -d "Show metric info for top of stack"
+complete -c gt -n "__fish_seen_subcommand_from metric" \
+    -a "list" -d "List all metric categories"
+complete -c gt -n "__fish_seen_subcommand_from metric" \
+    -a "compatible" -d "Check metric compatibility (top 2 values)"
+complete -c gt -n "__fish_seen_subcommand_from metric" \
+    -a "decimal set" -d "Switch to SI prefix mode (1000-based)"
+complete -c gt -n "__fish_seen_subcommand_from metric" \
+    -a "binary set" -d "Switch to IEC prefix mode (1024-based)"
+
+# metric <category> — list metrics in a category
+complete -c gt \
+    -n "__fish_seen_subcommand_from metric; and not __fish_seen_subcommand_from show list compatible 'decimal set' 'binary set'" \
+    -a "DataRate" -d "bps, Kbps, Mbps, Gbps, Tbps"
+complete -c gt \
+    -n "__fish_seen_subcommand_from metric; and not __fish_seen_subcommand_from show list compatible 'decimal set' 'binary set'" \
+    -a "DataSize" -d "bits, bytes, KB, MB, GB, …"
+complete -c gt \
+    -n "__fish_seen_subcommand_from metric; and not __fish_seen_subcommand_from show list compatible 'decimal set' 'binary set'" \
+    -a "Distance" -d "m, km, mi, ft, in, nm"
+complete -c gt \
+    -n "__fish_seen_subcommand_from metric; and not __fish_seen_subcommand_from show list compatible 'decimal set' 'binary set'" \
+    -a "Speed" -d "mps, kmh, mph, knots"
+complete -c gt \
+    -n "__fish_seen_subcommand_from metric; and not __fish_seen_subcommand_from show list compatible 'decimal set' 'binary set'" \
+    -a "Time" -d "ms, s, min, hr, day"
+complete -c gt \
+    -n "__fish_seen_subcommand_from metric; and not __fish_seen_subcommand_from show list compatible 'decimal set' 'binary set'" \
+    -a "Universal" -d "Cool (unitless)"
+complete -c gt \
+    -n "__fish_seen_subcommand_from metric; and not __fish_seen_subcommand_from show list compatible 'decimal set' 'binary set'" \
+    -a "Weight" -d "mg, g, kg, ton, lb, oz"
+
+# ── `custom` subcommand ──────────────────────────────────────────────────────
+
+complete -c gt -n "__fish_seen_subcommand_from custom" \
+    -a "show" -d "Show custom metric(s)"
+complete -c gt -n "__fish_seen_subcommand_from custom" \
+    -a "list" -d "List all custom metrics"
+complete -c gt -n "__fish_seen_subcommand_from custom" \
+    -a "define" -d "Define a new custom metric"
+complete -c gt -n "__fish_seen_subcommand_from custom" \
+    -a "undefine" -d "Remove a custom metric"
+
+# custom define <name> <factor> <category> — complete categories
+complete -c gt \
+    -n "__fish_seen_subcommand_from define" \
+    -a "Custom" -d "Custom (user-defined)"
+complete -c gt \
+    -n "__fish_seen_subcommand_from define" \
+    -a "DataRate" -d "Data rate category"
+complete -c gt \
+    -n "__fish_seen_subcommand_from define" \
+    -a "DataSize" -d "Data size category"
+complete -c gt \
+    -n "__fish_seen_subcommand_from define" \
+    -a "Distance" -d "Distance category"
+complete -c gt \
+    -n "__fish_seen_subcommand_from define" \
+    -a "Speed" -d "Speed category"
+complete -c gt \
+    -n "__fish_seen_subcommand_from define" \
+    -a "Time" -d "Time category"
+complete -c gt \
+    -n "__fish_seen_subcommand_from define" \
+    -a "Universal" -d "Universal (unitless)"
+complete -c gt \
+    -n "__fish_seen_subcommand_from define" \
+    -a "Weight" -d "Weight category"
diff --git a/internal/repl/completer.go b/internal/repl/completer.go
index f87209b..e19a521 100644
--- a/internal/repl/completer.go
+++ b/internal/repl/completer.go
@@ -84,6 +84,11 @@ func (a *AutoCompleteAdapter) completeCommands(lastWord string) ([][]rune, int)
 			matches = append(matches, []rune(cmd))
 		}
 	}
+	// If the word already exactly matches one command, don't offer it as a
+	// completion — readline would append it, giving e.g. "helphelp".
+	if len(matches) == 1 && string(matches[0]) == lastWord {
+		return nil, 0
+	}
 	return a.withCommonPrefix(matches, lastWord)
 }
 
diff --git a/internal/repl/completer_adapter_test.go b/internal/repl/completer_adapter_test.go
index 397a036..5f94a3b 100644
--- a/internal/repl/completer_adapter_test.go
+++ b/internal/repl/completer_adapter_test.go
@@ -48,19 +48,19 @@ func TestAutoCompleteAdapterDo(t *testing.T) {
 			wantLen:    len(commands),
 			wantMinLen: 0,
 		},
-		// Exact matches
+		// Exact matches — no completion offered (readline would append the word)
 		{
 			name:       "exact match help",
 			line:       []rune("help"),
 			pos:        4,
-			wantLen:    1,
+			wantLen:    0,
 			wantMinLen: 0,
 		},
 		{
 			name:       "exact match clear",
 			line:       []rune("clear"),
 			pos:        5,
-			wantLen:    1,
+			wantLen:    0,
 			wantMinLen: 0,
 		},
 		// Partial matches (single match, commonLen always 0 since minLen capped at len(lastWord))
@@ -165,12 +165,12 @@ func TestAutoCompleteAdapterDo(t *testing.T) {
 			wantLen:    2,
 			wantMinLen: -1,
 		},
-		// Multi-word input completes last word
+		// Multi-word input completes last word (exact match returns nothing)
 		{
 			name:       "multi word input completes last word",
 			line:       []rune("rpn help"),
 			pos:        8,
-			wantLen:    1,
+			wantLen:    0,
 			wantMinLen: 0,
 		},
 		// Cursor position matters
@@ -272,10 +272,10 @@ func TestAutoCompleteAdapterDoPreserveCommandOrder(t *testing.T) {
 func TestAutoCompleteAdapterDoMultilineInput(t *testing.T) {
 	adapter := NewAutoCompleter()
 
-	// Tab-separated words
+	// Tab-separated words — exact match "help" returns no completions
 	matches, _ := adapter.Do([]rune("rpn\thelp"), 8)
-	if len(matches) != 1 {
-		t.Errorf("tab-separated 'rpn\\thelp' should match 'help', got %d: %v",
+	if len(matches) != 0 {
+		t.Errorf("tab-separated 'rpn\\thelp' (exact match) should return 0, got %d: %v",
 			len(matches), runeSliceToStringSlice(matches))
 	}
 }