From e07873f67e32ffeea460bfdaab03a9d0e9567847 Mon Sep 17 00:00:00 2001
From: Billy Donahue <billy.donahue@mongodb.com>
Date: Mon, 20 Sep 2021 23:39:24 +0000
Subject: SERVER-59908 simplify extendedFCVTable use

---
 src/mongo/util/version/releases.h.tpl | 35 +++++++++++++++++------------------
 1 file changed, 17 insertions(+), 18 deletions(-)

diff --git a/src/mongo/util/version/releases.h.tpl b/src/mongo/util/version/releases.h.tpl
index 787494840cf..f006eed1ed1 100644
--- a/src/mongo/util/version/releases.h.tpl
+++ b/src/mongo/util/version/releases.h.tpl
@@ -223,21 +223,24 @@ inline constexpr std::array extendedFCVTable {
 #end for
 };
 
+constexpr decltype(auto) findExtended(FeatureCompatibilityVersion v) {
+    return extendedFCVTable[static_cast<size_t>(v)];
+}
+
+constexpr StringData toString(FeatureCompatibilityVersion v) {
+    return findExtended(v).second;
+}
+
 /**
- * A table with mappings between FeatureCompatibilityVersion::kVersion_X_Y and a pointer to the
- * "X.Y"_sd generated by the extended table. Thus, this a subset of the extended table.
+ * Pointers to nodes of the extended table that represent numbered software versions.
+ * Other FCV enum members, such as those representing transitions, are excluded.
  */
 inline constexpr std::array standardFCVTable {
 #for fcv, _ in filter(lambda p: p not in transition_fcvs, fcv_list):
-    std::pair{FeatureCompatibilityVersion::$fcv,
-        &extendedFCVTable[static_cast<size_t>(FeatureCompatibilityVersion::$fcv)].second},
+    &findExtended(FeatureCompatibilityVersion::$fcv),
 #end for
 };
 
-constexpr StringData toString(FeatureCompatibilityVersion v) {
-    return extendedFCVTable[static_cast<size_t>(v)].second;
-}
-
 /**
  * Parses 'versionString', of the form "X.Y", to its corresponding FCV enum. For example, "5.1"
  * will be parsed as FeatureCompatibilityVersion::$fcv_cpp_name(Version("5.1")).
@@ -245,11 +248,9 @@ constexpr StringData toString(FeatureCompatibilityVersion v) {
  * enum.
  */
 inline FeatureCompatibilityVersion parseVersionForFeatureFlags(StringData versionString) {
-    for (const auto& [fcv, record] : standardFCVTable) {
-        if (*record == versionString)
-            return fcv;
-    }
-
+    for (auto ptr : standardFCVTable)
+        if (ptr->second == versionString)
+            return ptr->first;
     uasserted(ErrorCodes::BadValue,
               fmt::format("Invalid FCV version {} for feature flag.", versionString));
 }
@@ -259,12 +260,10 @@ inline FeatureCompatibilityVersion parseVersionForFeatureFlags(StringData versio
  * version of the form 'X.Y'. Non-standard enums are transition enums, 'kInvalid' and
  * 'kUnsetDefaultLastLTSBehavior'.
  */
-inline bool isStandardFCV(FeatureCompatibilityVersion v) {
-    for (const auto& [fcv, record] : standardFCVTable) {
-        if (v == fcv)
+constexpr bool isStandardFCV(FeatureCompatibilityVersion v) {
+    for (auto ptr : standardFCVTable)
+        if (ptr->first == v)
             return true;
-    }
-
     return false;
 }
 
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