Merge pull request #1992 from xushiwei/q

mini spec: import package

doc/spec-mini.md

@@ -1736,4 +1736,40 @@ package math
 
 ### Import declarations
 
+An import declaration states that the source file containing the declaration depends on functionality of the `imported` package ([Program initialization and execution]()) and enables access to [exported]() identifiers of that package. The import names an identifier (PackageName) to be used for access and an ImportPath that specifies the package to be imported.
+
+```go
+ImportDecl       = "import" ( ImportSpec | "(" { ImportSpec ";" } ")" ) .
+ImportSpec       = [ "." | PackageName ] ImportPath .
+ImportPath       = string_lit .
+```
+
+The PackageName is used in [qualified identifiers]() to access exported identifiers of the package within the importing source file. It is declared in the [file block](). If the PackageName is omitted, it defaults to the identifier specified in the [package clause](#package-clause) of the imported package. If an explicit period (.) appears instead of a name, all the package's exported identifiers declared in that package's [package block]() will be declared in the importing source file's file block and must be accessed without a qualifier.
+
+The interpretation of the ImportPath is implementation-dependent but it is typically a substring of the full file name of the compiled package and may be relative to a repository of installed packages.
+
+Implementation restriction: A compiler may restrict ImportPaths to non-empty strings using only characters belonging to [Unicode's]() L, M, N, P, and S general categories (the Graphic characters without spaces) and may also exclude the characters !"#$%&'()*,:;<=>?[\]^`{|} and the Unicode replacement character U+FFFD.
+
+Consider a compiled a package containing the package clause package math, which exports function `Sin`, and installed the compiled package in the file identified by "lib/math". This table illustrates how `Sin` is accessed in files that import the package after the various types of import declaration.
+
+```go
+Import declaration          Local name of Sin
+
+import   "lib/math"         math.Sin
+import m "lib/math"         m.Sin
+import . "lib/math"         Sin
+```
+
+An import declaration declares a dependency relation between the importing and imported package. It is illegal for a package to import itself, directly or indirectly, or to directly import a package without referring to any of its exported identifiers. To import a package solely for its side-effects (initialization), use the [blank]() identifier as explicit package name:
+
+```go
+import _ "lib/math"
+```
+
+### An example package
+
+Here is a complete Go+ package that implements XXX.
+
+```go
 TODO
+```