build: preserve semantic version separators

SemVer separates pre-release identifiers and build metadata with
periods, but semanticAlphabet omits the period, so normalizeVerString
silently collapses beta.rc1 into betarc1.

btcwallet is the outlier in its own family: btcd version.go:14 and lnd
build/version.go:38 already allow the period, so the same
-ldflags "-X ...appBuild=exp.sha.5114f85" produces a different version
string in btcwallet than in btcd. This aligns them rather than changing
behaviour across the family.

appBuild is settable at build time via -ldflags, and SemVer build
metadata is dot-separated, so a build stamped with exp.sha.5114f85
currently reports expsha5114f85.

Note on the doc comments: semanticAlphabet is a per-character filter, so
allowing '.' also lets a malformed arrangement of valid characters
through ("beta." now survives where it was previously stripped). btcd
and lnd have the same naive filter, so this records the limitation
rather than diverging from them.

Author: pucedoteth

build/version.go

@@ -11,7 +11,7 @@ import (
 )
 
 // semanticAlphabet
-const semanticAlphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-"
+const semanticAlphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-."
 
 // These constants define the application version and follow the semantic
 // versioning 2.0.0 spec (http://semver.org/).
@@ -21,13 +21,19 @@ const (
 	appPatch uint = 1
 
 	// appPreRelease MUST only contain characters from semanticAlphabet
-	// per the semantic versioning spec.
+	// per the semantic versioning spec.  That is necessary but not
+	// sufficient: semanticAlphabet is a per-character filter and cannot
+	// reject a malformed arrangement of valid characters, such as a
+	// trailing or doubled '.', so the value must also be a well-formed
+	// dot-separated list of non-empty identifiers.
 	appPreRelease = "alpha"
 )
 
 // appBuild is defined as a variable so it can be overridden during the build
 // process with '-ldflags "-X main.appBuild foo' if needed.  It MUST only
-// contain characters from semanticAlphabet per the semantic versioning spec.
+// contain characters from semanticAlphabet per the semantic versioning spec,
+// and like appPreRelease must also be a well-formed dot-separated list of
+// non-empty identifiers, which the per-character filter cannot enforce.
 var appBuild string
 
 // Version returns the application version as a properly formed string per the

build/version_test.go

@@ -0,0 +1,46 @@
+// Copyright (c) 2026 The btcsuite developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package build
+
+import "testing"
+
+// TestNormalizeVerString ensures semantic version separators are preserved
+// while characters outside the alphabet are still stripped.
+func TestNormalizeVerString(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name string
+		in   string
+		want string
+	}{
+		{
+			name: "dotted pre-release identifier",
+			in:   "beta.rc1",
+			want: "beta.rc1",
+		},
+		{
+			// appBuild may be set to a dotted value via -ldflags at
+			// build time.
+			name: "dotted build metadata",
+			in:   "exp.sha.5114f85",
+			want: "exp.sha.5114f85",
+		},
+		{
+			// Guards against the filter being dropped entirely: an
+			// identity function satisfies the cases above.
+			name: "character outside the alphabet",
+			in:   "beta!rc1",
+			want: "betarc1",
+		},
+	}
+
+	for _, test := range tests {
+		if got := normalizeVerString(test.in); got != test.want {
+			t.Fatalf("%s: normalizeVerString(%q) = %q, want %q",
+				test.name, test.in, got, test.want)
+		}
+	}
+}