all: support multiple versions of Unicode

Different Go compilers support different versions of Unicode.
In general, one should match the version of x/text to match
the Unicode version of the Go core. This is quite painful and
restrictive in practice.

x/text now supports multiple versions of Unicode concurrently
which are selected based on the Go compiler used (from 1.7).

Change-Id: I9a999bf603872a88932740ca7eb518c247519e06
Reviewed-on: https://go-review.googlesource.com/83235
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

README.md

@@ -9,16 +9,18 @@ This repo uses Semantic versioning (http://semver.org/), so
    and
 1. PATCH version when you make backwards-compatible bug fixes.
 
-A Unicode major and minor version bump is mapped to a major version bump in
-x/text.
-A path version bump in Unicode is mapped to a minor version bump in x/text.
-Note that, consistent with the definitions in semver, until version 1.0.0 of
-x/text is reached, the minor version is considered a major version.
-So going from 0.1.0 to 0.2.0 is considered to be a major version bump.
+Until version 1.0.0 of x/text is reached, the minor version is considered a
+major version. So going from 0.1.0 to 0.2.0 is considered to be a major version
+bump.
 
 A major new CLDR version is mapped to a minor version increase in x/text.
 Any other new CLDR version is mapped to a patch version increase in x/text.
 
+It is important that the Unicode version used in `x/text` matches the one used
+by your Go compiler. The `x/text` repository supports multiple versions of
+Unicode and will match the version of Unicode to that of the Go compiler. At the
+moment this is supported for Go compilers from version 1.7.
+
 ## Download/Install
 
 The easiest way to install is to run `go get -u golang.org/x/text`. You can

cases/gen.go

@@ -207,7 +207,7 @@ func genTables() {
 	}
 
 	w := gen.NewCodeWriter()
-	defer w.WriteGoFile("tables.go", "cases")
+	defer w.WriteVersionedGoFile("tables.go", "cases")
 
 	gen.WriteUnicodeVersion(w)
 
@@ -761,7 +761,7 @@ func genTablesTest() {
 
 	fmt.Fprintln(w, ")")
 
-	gen.WriteGoFile("tables_test.go", "cases", w.Bytes())
+	gen.WriteVersionedGoFile("tables_test.go", "cases", w.Bytes())
 }
 
 // These functions are just used for verification that their definition have not