internal/core/runtime: new attribute name for extern

Right now, we only allow one type of extern attribute in
a file. At the file level, we define @extern(kind). Fields
within the file can then be associated with an @extern
attribute that is interpreted as defined by kind.

This approach may work for lower-level functionality like
support for WASM, but it seems a bit unintuitive for embed.
Instead, we suggest that after a file-level @extern(kind)
declaration the field attributes take the form @kind(). This
is what is implemented here.

This has the additional benefit that we could more easily
allow different types of extern fields within a single file.

Note that the original reason to reuse @extern for field
attributes was to avoid a proliferation of attributes.
This namespace encrouching is still a bit mitigated by the
@extern(kind) attribute. In the future we can find a different
mechanism to define attributes scoped by domain.

Issue #2031

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: I28b1fdd0f0a85c46a544f71bbff40a7772e60873
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1196717
Reviewed-by: Daniel Martí <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

internal/core/runtime/extern.go

@@ -245,22 +245,23 @@ func (d *externDecorator) markExternFieldAttr(kind string, decls []ast.Decl) (er
 
 		case *ast.Attribute:
 			key, body := x.Split()
-			if key != "extern" {
+			// Support old-style and new-style extern attributes.
+			if key != "extern" && key != kind {
 				break
 			}
 
 			lastField := len(fieldStack) - 1
 			if lastField < 0 {
 				errs = errors.Append(errs, errors.Newf(x.Pos(),
-					"extern attribute not associated with field"))
+					"@%s attribute not associated with field", kind))
 				return true
 			}
 
 			f := fieldStack[lastField]
 
 			if _, ok := d.fields[f]; ok {
 				errs = errors.Append(errs, errors.Newf(x.Pos(),
-					"duplicate extern attributes"))
+					"duplicate @%s attributes", kind))
 				return true
 			}
 

internal/core/runtime/testdata/basic.txtar

@@ -5,9 +5,9 @@
 package foo
 
 
-Foo: _ @extern(file1.xx, abi=c, sig="func(int)int")
+Foo: _ @test(file1.xx, abi=c, sig="func(int)int")
 
-Rename: _ @extern(file1.xx, name=Emaner, abi=c, sig="func(int)int")
+Rename: _ @test(file1.xx, name=Emaner, abi=c, sig="func(int)int")
 
 -- file2.cue --
 @extern("test")
@@ -17,7 +17,7 @@ package foo
 
 Bar: {
 	@other()
-	@extern(file2.xx, abi=c, sig="func(int)int")
+	@test(file2.xx, abi=c, sig="func(int)int")
 	_
 }
 

internal/core/runtime/testdata/compile.txtar

@@ -3,7 +3,7 @@
 
 package ok
 
-foo: _ @extern("file.xx", fail)
+foo: _ @test("file.xx", fail)
 -- out/extern --
 can't load from external module: TEST: fail compilation:
     ./compile.cue:5:8

internal/core/runtime/testdata/errors.txtar

@@ -13,30 +13,30 @@ package foo
 
 package foo
 
-Fn1: _ @extern("file1.xx" abi sig)
+Fn1: _ @test("file1.xx" abi sig)
 
 -- empty_extern.cue --
 @extern()
 
 package foo
 
-Fn2: _ @extern("file1.xx" abi sig)
+Fn2: _ @test("file1.xx" abi sig)
 
 
 -- unknown_interpreter.cue --
 @extern("wazem")
 
 package foo
 
-Fn3: _ @extern("file1.xx" abi sig)
+Fn3: _ @wazem("file1.xx" abi sig)
 
 -- double_extern_a.cue --
 @extern("test")
 @extern("test")
 
 package foo
 
-Fn4a: _ @extern("file1.xx")
+Fn4a: _ @test("file1.xx")
 
 -- double_extern_b.cue --
 @extern("test")
@@ -45,14 +45,14 @@ Fn4a: _ @extern("file1.xx")
 
 package foo
 
-Fn4b: _ @extern("file1.xx")
+Fn4b: _ @test("file1.xx")
 
 -- package_attr.cue --
 @extern("test")
 
 package foo
 
-@extern("file1.xx")
+@test("file1.xx")
 Fn5: _
 
 -- duplicate.cue --
@@ -61,39 +61,39 @@ Fn5: _
 package foo
 
 
-Fn6: _ @extern("file1.xx",sig=func(int)int) @extern("file1.xx", sig=func(int)bool)
+Fn6: _ @test("file1.xx",sig=func(int)int) @test("file1.xx", sig=func(int)bool)
 
 Fn7: {
-	@extern("file1.xx",sig=func(int)int)
+	@test("file1.xx",sig=func(int)int)
 	_
-} @extern("file1.xx", sig=func(int)bool)
+} @test("file1.xx", sig=func(int)bool)
 
 -- non_ident.cue --
 @extern("test")
 
 package foo
 
 
-"a-b": _ @extern("file1.xx",sig=func(int)int)
+"a-b": _ @test("file1.xx",sig=func(int)int)
 
-[string]: _ @extern("file1.xx",sig=func(int)int)
+[string]: _ @test("file1.xx",sig=func(int)int)
 
 -- late_extern.cue --
 package foo
 
 @extern("test")
 
 
-Foo: _ @extern(file1.xx, abi=c, sig="func(int)int")
+Foo: _ @test(file1.xx, abi=c, sig="func(int)int")
 
 -- out/extern --
 only one file-level extern attribute allowed per file:
     ./double_extern_a.cue:2:1
 only one file-level extern attribute allowed per file:
     ./double_extern_b.cue:2:1
-duplicate extern attributes:
-    ./duplicate.cue:6:45
-duplicate extern attributes:
+duplicate @test attributes:
+    ./duplicate.cue:6:43
+duplicate @test attributes:
     ./duplicate.cue:11:3
 interpreter name must be non-empty:
     ./empty_extern.cue:1:1
@@ -105,7 +105,7 @@ can only define functions for fields with identifier names, found "a-b":
     ./non_ident.cue:6:10
 can only define functions for fields with identifier names, found [string]:
     ./non_ident.cue:8:13
-extern attribute not associated with field:
+@test attribute not associated with field:
     ./package_attr.cue:5:1
 no interpreter defined for "wazem":
     ./unknown_interpreter.cue:1:1

internal/core/runtime/testdata/failinit.txtar

@@ -6,7 +6,7 @@
 package failinit
 
 
-foo: _ @extern("file.xx")
+foo: _ @test("file.xx")
 
 -- out/extern --
 TEST: fail initialization

internal/core/runtime/testdata/legacy.txtar

@@ -0,0 +1,30 @@
+-- cue.mod/modules.cue --
+-- file1.cue --
+@extern("test")
+
+package foo
+
+
+Foo: _ @extern(file1.xx, abi=c, sig="func(int)int")
+
+Rename: _ @extern(file1.xx, name=Emaner, abi=c, sig="func(int)int")
+
+-- file2.cue --
+@extern("test")
+
+package foo
+
+
+Bar: {
+	@other()
+	@extern(file2.xx, abi=c, sig="func(int)int")
+	_
+}
+
+-- extern/out --
+-- out/extern --
+{
+	Foo:    implFoo1
+	Bar:    implBar2
+	Rename: implEmaner1
+}

internal/core/runtime/testdata/nested.txtar

@@ -5,9 +5,9 @@
 package foo
 
 
-a: Foo: _ @extern(file1.xx, abi=c, sig="func(int)int")
+a: Foo: _ @test(file1.xx, abi=c, sig="func(int)int")
 
-a: Rename: _ @extern(file1.xx, name=Emaner, abi=c, sig="func(int)int")
+a: Rename: _ @test(file1.xx, name=Emaner, abi=c, sig="func(int)int")
 
 -- file2.cue --
 @extern("test")
@@ -17,7 +17,7 @@ package foo
 
 a: foo: Bar: {
 	@other()
-	@extern(file2.xx, abi=c, sig="func(int)int")
+	@test(file2.xx, abi=c, sig="func(int)int")
 	_
 }
 

internal/core/runtime/testdata/no_top_extern.txtar

@@ -8,7 +8,7 @@
 package foo
 
 
-Foo: _ @extern(file.xx, abi=c, sig="func(int)int")
+Foo: _ @test(file.xx, abi=c, sig="func(int)int")
 
 -- extern/out --
 -- out/extern/config --