clarify build requirements and add a check script for common errors

Makefile

@@ -4,9 +4,12 @@ all: honk
 schema.go: schema.sql
 	sh ./genschemago.sh
 
-honk: schema.go *.go go.mod
+honk: .preflightcheck schema.go *.go go.mod
 	go build -mod=`ls -d vendor 2> /dev/null` -o honk
 
+.preflightcheck: preflight.sh
+	@sh ./preflight.sh
+
 clean:
 	rm -f honk
 

README

@@ -20,7 +20,7 @@ This does not imply the goal is to be what you want.
 -- build
 
 It should be sufficient to type make after unpacking a release.
-You'll need a go compiler version 1.11 or later.
+You'll need a go compiler version 1.13 or later. And libsqlite3.
 
 Even on a fast machine, building from source can take several seconds.
 

docs/honk.8

@@ -41,7 +41,7 @@ proxy_set_header Host $http_host;
 .Ss Build
 Building
 .Nm
-requires a go compiler and libsqlite.
+requires a go compiler 1.13 and libsqlite.
 On
 .Ox
 this is the go and sqlite3 packages.

go.mod

@@ -1,6 +1,6 @@
 module humungus.tedunangst.com/r/honk
 
-go 1.11
+go 1.13
 
 require (
 	github.com/andybalholm/cascadia v1.1.0

preflight.sh

@@ -0,0 +1,30 @@
+set -e
+
+go version > /dev/null 2>&1 || (echo go 1.13+ is required && false)
+
+v=`go version | egrep -o 'go1[^ ]+'`
+case $v in
+	go1.10*|go1.11*|go1.12*)
+		echo go version is too old: $v
+		echo go 1.13+ is required
+		false
+		;;
+	go1.1*)
+		# just pretend nobody is still using go 1.1 or 1.2
+		;;
+	go1.2*)
+		;;
+	*)
+		echo unknown go version: $v
+		false
+		;;
+esac
+
+if [ \! \( -e /usr/include/sqlite3.h -o -e /usr/local/include/sqlite3.h \) ] ; then
+	echo unable to find sqlite3.h header
+	echo please install libsqlite3 dev package
+	false
+fi
+
+touch .preflightcheck
+