From 0253c0f4acdf9f7a2930609f55d24b334fa7d3c2 Mon Sep 17 00:00:00 2001
From: Tim King <taking@google.com>
Date: Mon, 5 Aug 2024 12:57:33 -0700
Subject: [PATCH] cmd/compile/internal/types2: change inference error message

Changes the type inference error message so that the position is
proceeded by a space. cmd/go rewrites the output of gc to replace
absolute paths at the beginning of lines and those proceeded by a
space or a tab to relative paths.

Updates testdir to do the same post processing on the output
of tests as cmd/go.

Fixes #68292

Change-Id: Ie109b51143e68f6e7ab4cd19064110db0e609a7e
Reviewed-on: https://go-review.googlesource.com/c/go/+/603097
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
---
 src/cmd/compile/internal/types2/infer.go |  2 +-
 src/cmd/internal/testdir/testdir_test.go | 22 +++++++++++++++++++++-
 src/go/types/infer.go                    |  2 +-
 test/fixedbugs/issue68292.go             | 12 ++++++++++++
 4 files changed, 35 insertions(+), 3 deletions(-)
 create mode 100644 test/fixedbugs/issue68292.go

diff --git a/src/cmd/compile/internal/types2/infer.go b/src/cmd/compile/internal/types2/infer.go
index 122ac9e04f..219942862f 100644
--- a/src/cmd/compile/internal/types2/infer.go
+++ b/src/cmd/compile/internal/types2/infer.go
@@ -431,7 +431,7 @@ func (check *Checker) infer(pos syntax.Pos, tparams []*TypeParam, targs []Type,
 	for i, typ := range inferred {
 		if typ == nil || isParameterized(tparams, typ) {
 			obj := tparams[i].obj
-			err.addf(pos, "cannot infer %s (%v)", obj.name, obj.pos)
+			err.addf(pos, "cannot infer %s (declared at %v)", obj.name, obj.pos)
 			return nil
 		}
 	}
diff --git a/src/cmd/internal/testdir/testdir_test.go b/src/cmd/internal/testdir/testdir_test.go
index c494f2c4c0..68fbdffb1d 100644
--- a/src/cmd/internal/testdir/testdir_test.go
+++ b/src/cmd/internal/testdir/testdir_test.go
@@ -1212,7 +1212,7 @@ func (t test) errorCheck(outStr string, wantAuto bool, fullshort ...string) (err
 	for i := range out {
 		for j := 0; j < len(fullshort); j += 2 {
 			full, short := fullshort[j], fullshort[j+1]
-			out[i] = strings.Replace(out[i], full, short, -1)
+			out[i] = replacePrefix(out[i], full, short)
 		}
 	}
 
@@ -1962,3 +1962,23 @@ func splitQuoted(s string) (r []string, err error) {
 	}
 	return args, err
 }
+
+// replacePrefix is like strings.ReplaceAll, but only replaces instances of old
+// that are preceded by ' ', '\t', or appear at the beginning of a line.
+//
+// This does the same kind of filename string replacement as cmd/go.
+// Pilfered from src/cmd/go/internal/work/shell.go .
+func replacePrefix(s, old, new string) string {
+	n := strings.Count(s, old)
+	if n == 0 {
+		return s
+	}
+
+	s = strings.ReplaceAll(s, " "+old, " "+new)
+	s = strings.ReplaceAll(s, "\n"+old, "\n"+new)
+	s = strings.ReplaceAll(s, "\n\t"+old, "\n\t"+new)
+	if strings.HasPrefix(s, old) {
+		s = new + s[len(old):]
+	}
+	return s
+}
diff --git a/src/go/types/infer.go b/src/go/types/infer.go
index d0f1c1caf4..4da4513c7b 100644
--- a/src/go/types/infer.go
+++ b/src/go/types/infer.go
@@ -434,7 +434,7 @@ func (check *Checker) infer(posn positioner, tparams []*TypeParam, targs []Type,
 	for i, typ := range inferred {
 		if typ == nil || isParameterized(tparams, typ) {
 			obj := tparams[i].obj
-			err.addf(posn, "cannot infer %s (%v)", obj.name, obj.pos)
+			err.addf(posn, "cannot infer %s (declared at %v)", obj.name, obj.pos)
 			return nil
 		}
 	}
diff --git a/test/fixedbugs/issue68292.go b/test/fixedbugs/issue68292.go
new file mode 100644
index 0000000000..2a0d826745
--- /dev/null
+++ b/test/fixedbugs/issue68292.go
@@ -0,0 +1,12 @@
+// errorcheck
+
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+func f[S any, T any](T) {}
+func g() {
+	f(0) // ERROR "in call to f, cannot infer S \(declared at issue68292.go:9:8\)"
+}