From 1745f965f5678ad4c953f4e5d1faf3126fe7d35d Mon Sep 17 00:00:00 2001
From: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Date: Fri, 20 Mar 2026 01:11:21 -0700
Subject: [PATCH 1/2] fix: respect TERM=dumb and NO_COLOR for ANSI escape codes

PrettyPrintErrorMessage unconditionally emitted ANSI escape codes,
which broke output in terminals that don't support them (TERM=dumb)
and tools that pipe the output.

Skip ANSI formatting when TERM is set to "dumb" or when NO_COLOR is
set, following the NO_COLOR convention (https://no-color.org/).

Fixes #105
---
 nilaway.go | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/nilaway.go b/nilaway.go
index 2c282fe5..ebc5006f 100644
--- a/nilaway.go
+++ b/nilaway.go
@@ -18,6 +18,7 @@ package nilaway
 
 import (
 	"fmt"
+	"os"
 	"regexp"
 
 	"go.uber.org/nilaway/accumulation"
@@ -57,8 +58,14 @@ var codeReferencePattern = regexp.MustCompile("\\`(.*?)\\`")
 var pathPattern = regexp.MustCompile(`"(.*?)"`)
 var nilabilityPattern = regexp.MustCompile(`([\(|^\t](?i)(found\s|must\sbe\s)(nilable|nonnil)[\)]?)`)
 
-// PrettyPrintErrorMessage is used in error reporting to post process and pretty print the output with colors
+// PrettyPrintErrorMessage is used in error reporting to post process and pretty print the output with colors.
+// It respects the TERM environment variable and NO_COLOR convention, skipping ANSI codes when
+// TERM is set to "dumb" or NO_COLOR is set.
 func PrettyPrintErrorMessage(msg string) string {
+	if os.Getenv("TERM") == "dumb" || os.Getenv("NO_COLOR") != "" {
+		return "error: " + msg
+	}
+
 	// TODO: below string parsing should not be required after  is implemented
 	errorStr := fmt.Sprintf("\x1b[%dm%s\x1b[0m", 31, "error: ")      // red
 	codeStr := fmt.Sprintf("\u001B[%dm%s\u001B[0m", 95, "`${1}`")    // magenta

From 234b23525841c480fa5b047498fcaaaea3846e3b Mon Sep 17 00:00:00 2001
From: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Date: Thu, 14 May 2026 17:06:41 -0700
Subject: [PATCH 2/2] fix: respect TERM=dumb and NO_COLOR in PrettyPrint
 default

Move the env check from PrettyPrintErrorMessage into the PrettyPrint flag
default in config/config.go per @yuxincs review. The -pretty-print flag
continues to override the default via the existing override path in run.

Closes #105
---
 config/config.go | 18 ++++++++++++++++--
 nilaway.go       |  7 -------
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/config/config.go b/config/config.go
index e78f6184..2a5a546d 100644
--- a/config/config.go
+++ b/config/config.go
@@ -19,6 +19,7 @@ import (
 	"flag"
 	"go/ast"
 	"go/types"
+	"os"
 	"reflect"
 	"strings"
 
@@ -26,6 +27,19 @@ import (
 	"golang.org/x/tools/go/analysis"
 )
 
+// defaultPrettyPrint returns the default for the PrettyPrint config option.
+// It respects the NO_COLOR and TERM=dumb conventions when no -pretty-print flag is provided.
+// https://no-color.org/ and POSIX terminal-capability conventions.
+func defaultPrettyPrint() bool {
+	if os.Getenv("NO_COLOR") != "" {
+		return false
+	}
+	if os.Getenv("TERM") == "dumb" {
+		return false
+	}
+	return true
+}
+
 // Config is the struct that stores the user-configurable options for NilAway.
 type Config struct {
 	// PrettyPrint indicates whether the error messages should be pretty printed.
@@ -148,7 +162,7 @@ func newFlagSet() flag.FlagSet {
 
 	// We do not keep the returned pointer to the flags because we will not use them directly here.
 	// Instead, we will use the flags through the analyzer's Flags field later.
-	_ = fs.Bool(PrettyPrintFlag, true, "Pretty print the error messages")
+	_ = fs.Bool(PrettyPrintFlag, defaultPrettyPrint(), "Pretty print the error messages")
 	_ = fs.Bool(GroupErrorMessagesFlag, true, "Group similar error messages")
 	_ = fs.String(IncludePkgsFlag, "", "Comma-separated list of packages to analyze")
 	_ = fs.String(ExcludePkgsFlag, "", "Comma-separated list of packages to exclude from analysis")
@@ -164,7 +178,7 @@ func newFlagSet() flag.FlagSet {
 func run(pass *analysis.Pass) (any, error) {
 	// Set up default values for the config.
 	conf := &Config{
-		PrettyPrint:        true,
+		PrettyPrint:        defaultPrettyPrint(),
 		GroupErrorMessages: true,
 		// If the user does not provide an include list, we give an empty package prefix to catch
 		// all packages.
diff --git a/nilaway.go b/nilaway.go
index ebc5006f..68fd5a36 100644
--- a/nilaway.go
+++ b/nilaway.go
@@ -18,7 +18,6 @@ package nilaway
 
 import (
 	"fmt"
-	"os"
 	"regexp"
 
 	"go.uber.org/nilaway/accumulation"
@@ -59,13 +58,7 @@ var pathPattern = regexp.MustCompile(`"(.*?)"`)
 var nilabilityPattern = regexp.MustCompile(`([\(|^\t](?i)(found\s|must\sbe\s)(nilable|nonnil)[\)]?)`)
 
 // PrettyPrintErrorMessage is used in error reporting to post process and pretty print the output with colors.
-// It respects the TERM environment variable and NO_COLOR convention, skipping ANSI codes when
-// TERM is set to "dumb" or NO_COLOR is set.
 func PrettyPrintErrorMessage(msg string) string {
-	if os.Getenv("TERM") == "dumb" || os.Getenv("NO_COLOR") != "" {
-		return "error: " + msg
-	}
-
 	// TODO: below string parsing should not be required after  is implemented
 	errorStr := fmt.Sprintf("\x1b[%dm%s\x1b[0m", 31, "error: ")      // red
 	codeStr := fmt.Sprintf("\u001B[%dm%s\u001B[0m", 95, "`${1}`")    // magenta