gopls/internal/analysis/undeclaredname: merge into CodeAction

This change removes the undeclaredname analyzer,
and instead computes it directly from the
protocol.QuickFix code action producer,
follow the same structure in CL 617035.

Also:
- include return types for undeclared function
- add basic return type test in missingfunction.txt,
the major functionality should be the same as
fromcall_returns.txt
- add more cases in TypesFromContext, and
corresponding tests.

Fixes golang/go#47558

Change-Id: Ic79cf2f07a3baee60631bf0b8f5c2b9f4f4393d0
GitHub-Last-Rev: 33b78d7
GitHub-Pull-Request: #538
Reviewed-on: https://go-review.googlesource.com/c/tools/+/623156
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>

gopls/doc/analyzers.md

@@ -842,26 +842,6 @@ Default: on.
 
 Package documentation: [timeformat](https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/timeformat)
 
-<a id='undeclaredname'></a>
-## `undeclaredname`: suggested fixes for "undeclared name: <>"
-
-
-This checker provides suggested fixes for type errors of the
-type "undeclared name: <>". It will either insert a new statement,
-such as:
-
-	<> :=
-
-or a new function declaration, such as:
-
-	func <>(inferred parameters) {
-		panic("implement me!")
-	}
-
-Default: on.
-
-Package documentation: [undeclaredname](https://pkg.go.dev/golang.org/x/tools/gopls/internal/analysis/undeclaredname)
-
 <a id='unmarshal'></a>
 ## `unmarshal`: report passing non-pointer or non-interface values to unmarshal
 

gopls/doc/features/diagnostics.md

@@ -197,6 +197,56 @@ func (f Foo) bar(s string, i int) string {
 }
 ```
 
+### `CreateUndeclared`: Create missing declaration for "undeclared name: X"
+
+A Go compiler error "undeclared name: X" indicates that a variable or function is being used before
+it has been declared in the current scope. In this scenario, gopls offers a quick fix to create the declaration.
+
+#### Declare a new variable
+
+When you reference a variable that hasn't been declared:
+
+```go
+func main() {
+  x := 42
+  min(x, y) // error: undefined: y
+}
+```
+
+The quick fix would be:
+
+```go
+func main() {
+  x := 42
+  y :=
+  min(x, y)
+}
+```
+
+#### Declare a new function
+
+Similarly, if you call a function that hasn't been declared:
+
+```go
+func main() {
+  var s string
+  s = doSomething(42) // error: undefined: doSomething
+}
+```
+
+Gopls will insert a new function declaration below,
+inferring its type from the call:
+
+```go
+func main() {
+  var s string
+  s = doSomething(42)
+}
+
+func doSomething(i int) string {
+  panic("unimplemented")
+}
+```
 <!--
 
 dorky details and deletia:

gopls/internal/doc/api.json

@@ -569,11 +569,6 @@
 							"Doc": "check for calls of (time.Time).Format or time.Parse with 2006-02-01\n\nThe timeformat checker looks for time formats with the 2006-02-01 (yyyy-dd-mm)\nformat. Internationally, \"yyyy-dd-mm\" does not occur in common calendar date\nstandards, and so it is more likely that 2006-01-02 (yyyy-mm-dd) was intended.",
 							"Default": "true"
 						},
-						{
-							"Name": "\"undeclaredname\"",
-							"Doc": "suggested fixes for \"undeclared name: \u003c\u003e\"\n\nThis checker provides suggested fixes for type errors of the\ntype \"undeclared name: \u003c\u003e\". It will either insert a new statement,\nsuch as:\n\n\t\u003c\u003e :=\n\nor a new function declaration, such as:\n\n\tfunc \u003c\u003e(inferred parameters) {\n\t\tpanic(\"implement me!\")\n\t}",
-							"Default": "true"
-						},
 						{
 							"Name": "\"unmarshal\"",
 							"Doc": "report passing non-pointer or non-interface values to unmarshal\n\nThe unmarshal analysis reports calls to functions such as json.Unmarshal\nin which the argument type is not a pointer or an interface.",
@@ -1255,12 +1250,6 @@
 			"URL": "https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/timeformat",
 			"Default": true
 		},
-		{
-			"Name": "undeclaredname",
-			"Doc": "suggested fixes for \"undeclared name: \u003c\u003e\"\n\nThis checker provides suggested fixes for type errors of the\ntype \"undeclared name: \u003c\u003e\". It will either insert a new statement,\nsuch as:\n\n\t\u003c\u003e :=\n\nor a new function declaration, such as:\n\n\tfunc \u003c\u003e(inferred parameters) {\n\t\tpanic(\"implement me!\")\n\t}",
-			"URL": "https://pkg.go.dev/golang.org/x/tools/gopls/internal/analysis/undeclaredname",
-			"Default": true
-		},
 		{
 			"Name": "unmarshal",
 			"Doc": "report passing non-pointer or non-interface values to unmarshal\n\nThe unmarshal analysis reports calls to functions such as json.Unmarshal\nin which the argument type is not a pointer or an interface.",

gopls/internal/golang/codeaction.go

@@ -302,7 +302,7 @@ func quickFix(ctx context.Context, req *codeActionsRequest) error {
 			continue
 		}
 
-		msg := typeError.Error()
+		msg := typeError.Msg
 		switch {
 		// "Missing method" error? (stubmethods)
 		// Offer a "Declare missing methods of INTERFACE" code action.
@@ -329,6 +329,17 @@ func quickFix(ctx context.Context, req *codeActionsRequest) error {
 				msg := fmt.Sprintf("Declare missing method %s.%s", si.Receiver.Obj().Name(), si.MethodName)
 				req.addApplyFixAction(msg, fixMissingCalledFunction, req.loc)
 			}
+
+		// "undeclared name: x" or "undefined: x" compiler error.
+		// Offer a "Create variable/function x" code action.
+		// See [fixUndeclared] for command implementation.
+		case strings.HasPrefix(msg, "undeclared name: "),
+			strings.HasPrefix(msg, "undefined: "):
+			path, _ := astutil.PathEnclosingInterval(req.pgf.File, start, end)
+			title := undeclaredFixTitle(path, msg)
+			if title != "" {
+				req.addApplyFixAction(title, fixCreateUndeclared, req.loc)
+			}
 		}
 	}
 

gopls/internal/golang/fix.go

@@ -14,7 +14,6 @@ import (
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/gopls/internal/analysis/embeddirective"
 	"golang.org/x/tools/gopls/internal/analysis/fillstruct"
-	"golang.org/x/tools/gopls/internal/analysis/undeclaredname"
 	"golang.org/x/tools/gopls/internal/analysis/unusedparams"
 	"golang.org/x/tools/gopls/internal/cache"
 	"golang.org/x/tools/gopls/internal/cache/parsego"
@@ -65,6 +64,7 @@ const (
 	fixInvertIfCondition       = "invert_if_condition"
 	fixSplitLines              = "split_lines"
 	fixJoinLines               = "join_lines"
+	fixCreateUndeclared        = "create_undeclared"
 	fixMissingInterfaceMethods = "stub_missing_interface_method"
 	fixMissingCalledFunction   = "stub_missing_called_function"
 )
@@ -99,7 +99,6 @@ func ApplyFix(ctx context.Context, fix string, snapshot *cache.Snapshot, fh file
 		// These match the Diagnostic.Category.
 		embeddirective.FixCategory: addEmbedImport,
 		fillstruct.FixCategory:     singleFile(fillstruct.SuggestedFix),
-		undeclaredname.FixCategory: singleFile(undeclaredname.SuggestedFix),
 
 		// Ad-hoc fixers: these are used when the command is
 		// constructed directly by logic in server/code_action.
@@ -110,6 +109,7 @@ func ApplyFix(ctx context.Context, fix string, snapshot *cache.Snapshot, fh file
 		fixInvertIfCondition:       singleFile(invertIfCondition),
 		fixSplitLines:              singleFile(splitLines),
 		fixJoinLines:               singleFile(joinLines),
+		fixCreateUndeclared:        singleFile(CreateUndeclared),
 		fixMissingInterfaceMethods: stubMissingInterfaceMethodsFixer,
 		fixMissingCalledFunction:   stubMissingCalledFunctionFixer,
 	}